Finding similar items in high dimensional spaces locality sensitive hashingDmitriy Selivanov
This document discusses using locality sensitive hashing (LSH) to efficiently find similar items in high-dimensional spaces. It describes how LSH works by first representing items as sets of shingles/n-grams, then using minhashing to map these sets to compact signatures while preserving similarity. It explains that LSH further hashes the signatures into "bands" to generate candidate pairs that are likely similar and need direct comparison. The number of bands can be tuned to tradeoff between finding most similar pairs vs few dissimilar pairs.
Locality Sensitive Hashing (LSH) is a technique for solving near neighbor queries in high dimensional spaces. It works by using random projections to map similar data points to the same "buckets" with high probability, allowing efficient retrieval of nearest neighbors. The key properties required of the hash functions used are that they are locality sensitive, meaning nearby points are hashed to the same value more often than distant points. LSH allows solving near neighbor queries approximately in sub-linear time versus expensive exact algorithms like kd-trees that require at least linear time.
Locality sensitive hashing (LSH) is a technique to improve the efficiency of near neighbor searches in high-dimensional spaces. LSH works by hash functions that map similar items to the same buckets with high probability. The document discusses applications of near neighbor searching, defines the near neighbor reporting problem, and introduces LSH. It also covers techniques like gap amplification to improve LSH performance and parameter optimization to minimize query time.
Locality Sensitive Hashing (LSH) is a technique for finding similar items in large datasets. It works in 3 steps:
1. Shingling converts documents to sets of n-grams (sequences of tokens). This represents documents as high-dimensional vectors.
2. MinHashing maps these high-dimensional sets to short signatures or sketches, in a way that preserves similarity according to the Jaccard coefficient. It uses random permutations to select the minimum value in each permutation.
3. LSH partitions the signature matrix into bands and hashes each band separately, so that similar signatures are likely to hash to the same buckets. Candidate pairs are those that share buckets in one or more bands, reducing
In this project I use a stack of denoising autoencoders to learn low-dimensional
representations of images. These encodings are used as input to a locality sensitive
hashing algorithm to find images similar to a given query image. The results clearly
shows that this approach outperforms basic LSH by far.
This document summarizes research presented at the 24th Annual Symposium on Combinatorial Pattern Matching. It discusses three open problems in optimally encoding Straight Line Programs (SLPs), which are compressed representations of strings. The document presents information theoretic lower bounds on SLP size and describes novel techniques for building optimal encodings of SLPs in close to minimal space. It also proposes a space-efficient data structure for the reverse dictionary of an SLP.
This document discusses dynamic pathfinding algorithms. It begins with an overview of A* pathfinding and how it works. It then explains how dynamic pathfinding algorithms differ by modifying search data when the graph connections change, rather than recomputing the entire path from scratch. The document focuses on the dynamic pathfinding algorithms D* Lite and LPA*, explaining how they use node inconsistency checks and priority queue reordering to efficiently handle changes in the graph structure during a search.
This document describes a technique called MinHashing that can be used to efficiently find near-duplicate documents among a large collection. MinHashing works in three steps: 1) it converts documents to sets of shingles, 2) it computes signatures for the sets using MinHashing to preserve similarity, 3) it uses Locality-Sensitive Hashing to focus on signature pairs likely to be from similar documents, finding candidates efficiently. This avoids comparing all possible document pairs.
The document discusses how hash maps work and the process of rehashing. It explains that inserting a key-value pair into a hash map involves: 1) Hashing the key to get an index, 2) Searching the linked list at that index for an existing key, updating its value if found or adding a new node. Rehashing is done when the load factor increases above a threshold, as that increases lookup time. Rehashing doubles the size of the array and rehashes all existing entries to maintain a low load factor and constant time lookups.
This document discusses hashing techniques for storing data in a hash table. It describes hash collisions that can occur when multiple keys map to the same hash value. Two primary techniques for dealing with collisions are chaining and open addressing. Open addressing resolves collisions by probing to subsequent table indices, but this can cause clustering issues. The document proposes various rehashing functions that incorporate secondary hash values or quadratic probing to reduce clustering in open addressing schemes.
Hashing is a common technique for implementing dictionaries that provides constant-time operations by mapping keys to table positions using a hash function, though collisions require resolution strategies like separate chaining or open addressing. Popular hash functions include division and cyclic shift hashing to better distribute keys across buckets. Both open hashing using linked lists and closed hashing using linear probing can provide average constant-time performance for dictionary operations depending on load factor.
This document discusses hashing and different techniques for implementing dictionaries using hashing. It begins by explaining that dictionaries store elements using keys to allow for quick lookups. It then discusses different data structures that can be used, focusing on hash tables. The document explains that hashing allows for constant-time lookups on average by using a hash function to map keys to table positions. It discusses collision resolution techniques like chaining, linear probing, and double hashing to handle collisions when the hash function maps multiple keys to the same position.
Hashing has witnessed an increase in popularity over the
past few years due to the promise of compact encoding and fast query
time. In order to be effective hashing methods must maximally preserve
the similarity between the data points in the underlying binary representation.
The current best performing hashing techniques have utilised
supervision. In this paper we propose a two-step iterative scheme, Graph
Regularised Hashing (GRH), for incrementally adjusting the positioning
of the hashing hypersurfaces to better conform to the supervisory signal:
in the first step the binary bits are regularised using a data similarity
graph so that similar data points receive similar bits. In the second
step the regularised hashcodes form targets for a set of binary classifiers
which shift the position of each hypersurface so as to separate opposite
bits with maximum margin. GRH exhibits superior retrieval accuracy to
competing hashing methods.
From Trill to Quill: Pushing the Envelope of Functionality and ScaleBadrish Chandramouli
In this talk, I overview Trill, describe two projects that expand Trill's functionality, and describe Quill, a new multi-node offline analytics system I have been working on at MSR.
DASH: A C++ PGAS Library for Distributed Data Structures and Parallel Algorit...Menlo Systems GmbH
DASH is a C++ PGAS library that provides distributed data structures and parallel algorithms. It offers a global address space without a custom compiler. DASH partitions data across multiple units through various distribution patterns. It supports distributed multidimensional arrays and efficient local and global access to data. DASH includes many parallel algorithms ported from STL and supports asynchronous communication. It aims to simplify programming distributed applications through its data-oriented approach.
Introduction to Ultra-succinct representation of ordered trees with applicationsYu Liu
The document summarizes a paper on ultra-succinct representations of ordered trees. It introduces tree degree entropy, a new measure of information in trees. It presents a succinct data structure that uses nH*(T) + O(n log log n / log n) bits to represent an ordered tree T with n nodes, where H*(T) is the tree degree entropy. This representation supports computing consecutive bits of the tree's DFUDS representation in constant time. It also supports computing operations like lowest common ancestor, depth, and level-ancestor in constant time using an auxiliary structure of O(n(log log n)2 / log n) bits.
This document discusses sampled-data systems and provides examples of:
1. Models of analog-to-digital and digital-to-analog converters using sampler and zero-order hold blocks.
2. Deriving the discrete-time model from the continuous-time model using a zero-order hold.
3. An example of obtaining the state-space equations and transfer function of a discrete-time system from a continuous-time system.
This document presents an overview of making matrix multiplication algorithms more I/O efficient. It discusses the parallel disk model and how to incorporate locality into algorithms to minimize I/O steps. Cannon's algorithm for matrix multiplication in a 2D mesh network is described. Loop interchange is discussed as a way to improve cache efficiency when multiplying matrices by exploring different loop orderings. Results are shown for parallel I/O efficient matrix multiplication on different sized matrices, with times ranging from 0.38 to 7 seconds. References on cache-oblivious algorithms and distributed memory matrix multiplication are provided.
Hashing involves using an algorithm to generate a numeric key from input data. It maps keys to integers in order to store and retrieve data more efficiently. A simple hashing algorithm uses the modulus operator (%) to distribute keys uniformly. Hashing is commonly used for file management, comparing complex values, and cryptography. Collisions occur when different keys hash to the same value, requiring strategies like open hashing, closed hashing, or deleting data. Closed hashing supplements the hash table with linked lists to store colliding entries outside the standard table.
This document provides an overview of hashing techniques. It defines hashing as transforming a string into a shorter fixed-length value to represent the original string. Collisions occur when two different keys map to the same address. The document then describes a simple hashing algorithm involving three steps: representing the key numerically, folding and adding the numerical values, and dividing by the address space size. It also discusses predicting the distribution of records among addresses and estimating collisions for a full hash table.
The document discusses hashing techniques for storing and retrieving data from memory. It covers hash functions, hash tables, open addressing techniques like linear probing and quadratic probing, and closed hashing using separate chaining. Hashing maps keys to memory addresses using a hash function to store and find data independently of the number of items. Collisions may occur and different collision resolution methods are used like open addressing that resolves collisions by probing in the table or closed hashing that uses separate chaining with linked lists. The efficiency of hashing depends on factors like load factor and average number of probes.
The document discusses using geohashes to enable spatial search within Apache Solr. It describes how geohashes encode latitude and longitude data hierarchically and can be used to filter search results by geographic bounding boxes through indexing documents by their geohash prefixes. The author outlines his strategy for implementing geohash-based spatial search in Solr by calculating overlapping geohash prefixes, developing a filtering query, and indexing multi-precision geohashes for more efficient searching.
This document provides an overview of probabilistic data structures including Bloom filters, Cuckoo filters, Count-Min sketch, majority algorithm, linear counting, LogLog, HyperLogLog, locality sensitive hashing, minhash, and simhash. It discusses how Bloom filters work using hash functions to insert elements into a bit array and can tell if an element is likely present or definitely not present. It also explains how Count-Min sketch tracks frequencies in a stream using hash functions and finding the minimum value in each hash table cell. Finally, it summarizes how HyperLogLog estimates cardinality by tracking the maximum number of leading zeros when hashing random numbers.
This document discusses different searching methods like sequential, binary, and hashing. It defines searching as finding an element within a list. Sequential search searches lists sequentially until the element is found or the end is reached, with efficiency of O(n) in worst case. Binary search works on sorted arrays by eliminating half of remaining elements at each step, with efficiency of O(log n). Hashing maps keys to table positions using a hash function, allowing searches, inserts and deletes in O(1) time on average. Good hash functions uniformly distribute keys and generate different hashes for similar keys.
This document discusses dictionaries and hashing techniques for implementing dictionaries. It describes dictionaries as data structures that map keys to values. The document then discusses using a direct access table to store key-value pairs, but notes this has problems with negative keys or large memory usage. It introduces hashing to map keys to table indices using a hash function, which can cause collisions. To handle collisions, the document proposes chaining where each index is a linked list of key-value pairs. Finally, it covers common hash functions and analyzing load factor and collision probability.
The document contains programs demonstrating string and numeric conversion routines in 8086 assembly language. It includes examples of (1) block transfer of strings from one memory location to another, (2) insertion of a string into another string at a specified location, (3) deletion of a substring from a string, and (4) conversions between BCD, hexadecimal, and ASCII numeric representations. The programs utilize common string and arithmetic operations like MOVSB, LODSB, STOSB, DIV, MUL, AND, SHR to manipulate strings and perform conversions.
Hashing is a technique used to store and retrieve data efficiently. It involves using a hash function to map keys to integers that are used as indexes in an array. This improves searching time from O(n) to O(1) on average. However, collisions can occur when different keys map to the same index. Collision resolution techniques like chaining and open addressing are used to handle collisions. Chaining resolves collisions by linking keys together in buckets, while open addressing resolves them by probing to find the next empty index. Both approaches allow basic dictionary operations like insertion and search to be performed in O(1) average time when load factors are low.
This document contains descriptions of 6 graphs with their corresponding x and y coordinates. Each graph defines a function by mapping x-values from their domain to y-values in their range. The graphs demonstrate different types of functions, including linear, constant, and piecewise functions. Geogebra is also mentioned as a tool that can be used to find the area under curves.
Sketching and locality sensitive hashing for alignmentssuser2be88c
Sketching and locality sensitive hashing techniques are used to speed up large-scale sequence alignment problems by avoiding all-pairs comparisons. Locality sensitive hashing maps similar sequences to the same "buckets" with high probability, allowing near neighbors to be identified quickly. Ordered minhash is a locality sensitive hashing method for edit distance that accounts for k-mer repetition, providing a better approximation of sequence similarity than regular minhash. These techniques enable faster genome assembly and database searches by prioritizing sequence pairs that are more likely to align.
The document discusses how hash maps work and the process of rehashing. It explains that inserting a key-value pair into a hash map involves: 1) Hashing the key to get an index, 2) Searching the linked list at that index for an existing key, updating its value if found or adding a new node. Rehashing is done when the load factor increases above a threshold, as that increases lookup time. Rehashing doubles the size of the array and rehashes all existing entries to maintain a low load factor and constant time lookups.
This document discusses hashing techniques for storing data in a hash table. It describes hash collisions that can occur when multiple keys map to the same hash value. Two primary techniques for dealing with collisions are chaining and open addressing. Open addressing resolves collisions by probing to subsequent table indices, but this can cause clustering issues. The document proposes various rehashing functions that incorporate secondary hash values or quadratic probing to reduce clustering in open addressing schemes.
Hashing is a common technique for implementing dictionaries that provides constant-time operations by mapping keys to table positions using a hash function, though collisions require resolution strategies like separate chaining or open addressing. Popular hash functions include division and cyclic shift hashing to better distribute keys across buckets. Both open hashing using linked lists and closed hashing using linear probing can provide average constant-time performance for dictionary operations depending on load factor.
This document discusses hashing and different techniques for implementing dictionaries using hashing. It begins by explaining that dictionaries store elements using keys to allow for quick lookups. It then discusses different data structures that can be used, focusing on hash tables. The document explains that hashing allows for constant-time lookups on average by using a hash function to map keys to table positions. It discusses collision resolution techniques like chaining, linear probing, and double hashing to handle collisions when the hash function maps multiple keys to the same position.
Hashing has witnessed an increase in popularity over the
past few years due to the promise of compact encoding and fast query
time. In order to be effective hashing methods must maximally preserve
the similarity between the data points in the underlying binary representation.
The current best performing hashing techniques have utilised
supervision. In this paper we propose a two-step iterative scheme, Graph
Regularised Hashing (GRH), for incrementally adjusting the positioning
of the hashing hypersurfaces to better conform to the supervisory signal:
in the first step the binary bits are regularised using a data similarity
graph so that similar data points receive similar bits. In the second
step the regularised hashcodes form targets for a set of binary classifiers
which shift the position of each hypersurface so as to separate opposite
bits with maximum margin. GRH exhibits superior retrieval accuracy to
competing hashing methods.
From Trill to Quill: Pushing the Envelope of Functionality and ScaleBadrish Chandramouli
In this talk, I overview Trill, describe two projects that expand Trill's functionality, and describe Quill, a new multi-node offline analytics system I have been working on at MSR.
DASH: A C++ PGAS Library for Distributed Data Structures and Parallel Algorit...Menlo Systems GmbH
DASH is a C++ PGAS library that provides distributed data structures and parallel algorithms. It offers a global address space without a custom compiler. DASH partitions data across multiple units through various distribution patterns. It supports distributed multidimensional arrays and efficient local and global access to data. DASH includes many parallel algorithms ported from STL and supports asynchronous communication. It aims to simplify programming distributed applications through its data-oriented approach.
Introduction to Ultra-succinct representation of ordered trees with applicationsYu Liu
The document summarizes a paper on ultra-succinct representations of ordered trees. It introduces tree degree entropy, a new measure of information in trees. It presents a succinct data structure that uses nH*(T) + O(n log log n / log n) bits to represent an ordered tree T with n nodes, where H*(T) is the tree degree entropy. This representation supports computing consecutive bits of the tree's DFUDS representation in constant time. It also supports computing operations like lowest common ancestor, depth, and level-ancestor in constant time using an auxiliary structure of O(n(log log n)2 / log n) bits.
This document discusses sampled-data systems and provides examples of:
1. Models of analog-to-digital and digital-to-analog converters using sampler and zero-order hold blocks.
2. Deriving the discrete-time model from the continuous-time model using a zero-order hold.
3. An example of obtaining the state-space equations and transfer function of a discrete-time system from a continuous-time system.
This document presents an overview of making matrix multiplication algorithms more I/O efficient. It discusses the parallel disk model and how to incorporate locality into algorithms to minimize I/O steps. Cannon's algorithm for matrix multiplication in a 2D mesh network is described. Loop interchange is discussed as a way to improve cache efficiency when multiplying matrices by exploring different loop orderings. Results are shown for parallel I/O efficient matrix multiplication on different sized matrices, with times ranging from 0.38 to 7 seconds. References on cache-oblivious algorithms and distributed memory matrix multiplication are provided.
Hashing involves using an algorithm to generate a numeric key from input data. It maps keys to integers in order to store and retrieve data more efficiently. A simple hashing algorithm uses the modulus operator (%) to distribute keys uniformly. Hashing is commonly used for file management, comparing complex values, and cryptography. Collisions occur when different keys hash to the same value, requiring strategies like open hashing, closed hashing, or deleting data. Closed hashing supplements the hash table with linked lists to store colliding entries outside the standard table.
This document provides an overview of hashing techniques. It defines hashing as transforming a string into a shorter fixed-length value to represent the original string. Collisions occur when two different keys map to the same address. The document then describes a simple hashing algorithm involving three steps: representing the key numerically, folding and adding the numerical values, and dividing by the address space size. It also discusses predicting the distribution of records among addresses and estimating collisions for a full hash table.
The document discusses hashing techniques for storing and retrieving data from memory. It covers hash functions, hash tables, open addressing techniques like linear probing and quadratic probing, and closed hashing using separate chaining. Hashing maps keys to memory addresses using a hash function to store and find data independently of the number of items. Collisions may occur and different collision resolution methods are used like open addressing that resolves collisions by probing in the table or closed hashing that uses separate chaining with linked lists. The efficiency of hashing depends on factors like load factor and average number of probes.
The document discusses using geohashes to enable spatial search within Apache Solr. It describes how geohashes encode latitude and longitude data hierarchically and can be used to filter search results by geographic bounding boxes through indexing documents by their geohash prefixes. The author outlines his strategy for implementing geohash-based spatial search in Solr by calculating overlapping geohash prefixes, developing a filtering query, and indexing multi-precision geohashes for more efficient searching.
This document provides an overview of probabilistic data structures including Bloom filters, Cuckoo filters, Count-Min sketch, majority algorithm, linear counting, LogLog, HyperLogLog, locality sensitive hashing, minhash, and simhash. It discusses how Bloom filters work using hash functions to insert elements into a bit array and can tell if an element is likely present or definitely not present. It also explains how Count-Min sketch tracks frequencies in a stream using hash functions and finding the minimum value in each hash table cell. Finally, it summarizes how HyperLogLog estimates cardinality by tracking the maximum number of leading zeros when hashing random numbers.
This document discusses different searching methods like sequential, binary, and hashing. It defines searching as finding an element within a list. Sequential search searches lists sequentially until the element is found or the end is reached, with efficiency of O(n) in worst case. Binary search works on sorted arrays by eliminating half of remaining elements at each step, with efficiency of O(log n). Hashing maps keys to table positions using a hash function, allowing searches, inserts and deletes in O(1) time on average. Good hash functions uniformly distribute keys and generate different hashes for similar keys.
This document discusses dictionaries and hashing techniques for implementing dictionaries. It describes dictionaries as data structures that map keys to values. The document then discusses using a direct access table to store key-value pairs, but notes this has problems with negative keys or large memory usage. It introduces hashing to map keys to table indices using a hash function, which can cause collisions. To handle collisions, the document proposes chaining where each index is a linked list of key-value pairs. Finally, it covers common hash functions and analyzing load factor and collision probability.
The document contains programs demonstrating string and numeric conversion routines in 8086 assembly language. It includes examples of (1) block transfer of strings from one memory location to another, (2) insertion of a string into another string at a specified location, (3) deletion of a substring from a string, and (4) conversions between BCD, hexadecimal, and ASCII numeric representations. The programs utilize common string and arithmetic operations like MOVSB, LODSB, STOSB, DIV, MUL, AND, SHR to manipulate strings and perform conversions.
Hashing is a technique used to store and retrieve data efficiently. It involves using a hash function to map keys to integers that are used as indexes in an array. This improves searching time from O(n) to O(1) on average. However, collisions can occur when different keys map to the same index. Collision resolution techniques like chaining and open addressing are used to handle collisions. Chaining resolves collisions by linking keys together in buckets, while open addressing resolves them by probing to find the next empty index. Both approaches allow basic dictionary operations like insertion and search to be performed in O(1) average time when load factors are low.
This document contains descriptions of 6 graphs with their corresponding x and y coordinates. Each graph defines a function by mapping x-values from their domain to y-values in their range. The graphs demonstrate different types of functions, including linear, constant, and piecewise functions. Geogebra is also mentioned as a tool that can be used to find the area under curves.
Sketching and locality sensitive hashing for alignmentssuser2be88c
Sketching and locality sensitive hashing techniques are used to speed up large-scale sequence alignment problems by avoiding all-pairs comparisons. Locality sensitive hashing maps similar sequences to the same "buckets" with high probability, allowing near neighbors to be identified quickly. Ordered minhash is a locality sensitive hashing method for edit distance that accounts for k-mer repetition, providing a better approximation of sequence similarity than regular minhash. These techniques enable faster genome assembly and database searches by prioritizing sequence pairs that are more likely to align.
Expressing and Exploiting Multi-Dimensional Locality in DASHMenlo Systems GmbH
DASH is a realization of the PGAS (partitioned global address space) programming model in the form of a C++ template library. It provides a multidimensional array abstraction which is typically used as an underlying container for stencil- and dense matrix operations.
Efficiency of operations on a distributed multi-dimensional array highly depends on the distribution of its elements to processes and the communication strategy used to propagate values between them. Locality can only be improved by employing an optimal distribution that is specific to the implementation of the algorithm, run-time parameters such as node topology, and numerous additional aspects. Application developers do not know these implications which also might change in future releases of DASH.
In the following, we identify fundamental properties of distribution patterns that are prevalent in existing HPC applications.
We describe a classification scheme of multi-dimensional distributions based on these properties and demonstrate how distribution patterns can be optimized for locality and communication avoidance automatically and, to a great extent, at compile time.
This document provides information about various Linux clusters and distributed resource managers available at the Center for Genome Science and NIH. It lists several Linux cluster machines including KHAN with 94 nodes, KGENE with 28 nodes, and LOGIN and LOGINDB servers. Details are provided about the KHAN cluster including its node configuration, storage space, and available software. It also briefly mentions distributed resource managers.
This document provides information about various Linux clusters and distributed resource managers available at the Center for Genome Science and NIH. It lists several Linux cluster machines including KHAN, KGENE, LOGIN, LOGINDB, and DEV. Details are provided about the KHAN cluster, which has a total of 94 nodes, including specifications of the nodes and storage and software information. It also briefly mentions distributed resource managers.
Massively Scalable Real-time Geospatial Data Processing with Apache Kafka and...Paul Brebner
Geospatial data makes it possible to leverage location, location, location! Geospatial data is taking off, as companies realize that just about everyone needs the benefits of geospatially aware applications. As a result there are no shortages of unique but demanding use cases of how enterprises are leveraging large-scale and fast geospatial big data processing. The data must be processed in large quantities - and quickly - to reveal hidden spatiotemporal insights vital to businesses and their end users. In the rush to tap into geospatial data, many enterprises will find that representing, indexing and querying geospatially-enriched data is more complex than they anticipated - and might bring about tradeoffs between accuracy, latency, and throughput.This presentation will explore how we added location data to a scalable real-time anomaly detection application, built around Apache Kafka, and Cassandra. Kafka and Cassandra are designed for time-series data, however, it’s not so obvious how they can process geospatial data. In order to find location-specific anomalies, we need a way to represent locations, index locations, and query locations. We explore alternative geospatial representations including: Latitude/Longitude points, Bounding Boxes, Geohashes, and go vertical with 3D representations, including 3D Geohashes. To conclude we measure and compare the query throughput of some of the solutions, and summarise the results in terms of accuracy vs. performance to answer the question “Which geospatial data representation and Cassandra implementation is best?”
Massively Scalable Real-time Geospatial Data Processing with Apache Kafka and...Paul Brebner
This presentation will explore how we added location data to a scalable real-time anomaly detection application, built around Apache Kafka, and Cassandra.
Kafka and Cassandra are designed for time-series data, however, it’s not so obvious how they can process geospatial data. In order to find location-specific anomalies, we need a way to represent locations, index locations, and query locations.
We explore alternative geospatial representations including: Latitude/Longitude points, Bounding Boxes, Geohashes, and go vertical with 3D representations, including 3D Geohashes.
For each representation we also explore possible Cassandra implementations including: Clustering columns, Secondary indexes, Denormalized tables, and the Cassandra Lucene Index Plugin.
To conclude we measure and compare the query throughput of some of the solutions, and summarise the results in terms of accuracy vs. performance to answer the question “Which geospatial data representation and Cassandra implementation is best?”
Updated version of presentation for 30 April 2020 Melbourne Distributed Meetup (online)
Enterprise Scale Topological Data Analysis Using SparkAlpine Data
This document discusses scaling topological data analysis (TDA) using the Mapper algorithm to analyze large datasets. It describes how the authors built the first open-source scalable implementation of Mapper called Betti Mapper using Spark. Betti Mapper uses locality-sensitive hashing to bin data points and compute topological summaries on prototype points to achieve an 8-11x performance improvement over a naive Spark implementation. The key aspects of Betti Mapper that enable scaling to enterprise datasets are locality-sensitive hashing for sampling and using prototype points to reduce the distance matrix computation.
Enterprise Scale Topological Data Analysis Using SparkSpark Summit
This document discusses scaling topological data analysis (TDA) using the Mapper algorithm to analyze large datasets. It introduces Mapper and its computational bottlenecks. It then describes Betti Mapper, the authors' open-source scalable implementation of Mapper on Spark that achieves an 8-11x performance improvement over a naive version. Betti Mapper uses locality-sensitive hashing to bin data points and compute topological networks on prototype points to analyze large datasets enterprise-scale.
In KDD2011, Vijay Narayanan (Yahoo!) and Milind Bhandarkar (Greenplum Labs, EMC) conducted a tutorial on "Modeling with Hadoop". This is the first half of the tutorial.
Faster persistent data structures through hashingJohan Tibell
This document summarizes work to optimize persistent hash map data structures for faster performance. It begins by describing a use case needing fast lookups of string keys. Various implementations are evaluated, including binary search trees, hash tables, and Milan Straka's IntMap approach using hashing. The document then introduces the hash-array mapped trie (HAMT) data structure, describes an optimized Haskell implementation, and benchmarks showing it outperforms the IntMap approach with up to 76% faster lookups and 39-44% faster mutations. Memory usage is also improved over the IntMap. Overall, the HAMT provides the best combination of performance and memory efficiency for this persistent hash map use case.
Support Vector Machines in MapReduce presented an overview of support vector machines (SVMs) and how to implement them in a MapReduce framework to handle large datasets. The document discussed the theory behind basic linear SVMs and generalized multi-classification SVMs. It explained how to parallelize SVM training using stochastic gradient descent and randomly distributing samples across mappers and reducers. The document also addressed handling non-linear SVMs using kernel methods and approximations that allow SVMs to be treated as a linear problem in MapReduce. Finally, examples were given of large companies using SVMs trained on MapReduce to perform customer segmentation and improve inventory value.
Apache Cassandra is a highly scalable, distributed, decentralized, open-source NoSQL database. It provides availability, partition tolerance, and scalability without sacrificing consistency. Cassandra's data model is a keyed column store and it uses consistent hashing to distribute data across nodes. It also uses an eventual consistency model to provide high availability even in the presence of network issues.
Distributed approximate spectral clustering for large scale datasetsBita Kazemi
The document proposes a distributed approximate spectral clustering (DASC) algorithm to process large datasets in a scalable way. DASC uses locality sensitive hashing to group similar data points and then approximates the kernel matrix on each group to reduce computation. It implements DASC using MapReduce and evaluates it on real and synthetic datasets, showing it can achieve similar clustering accuracy to standard spectral clustering but with an order of magnitude better runtime by distributing the computation across clusters.
The document provides an introduction to hashing techniques and their applications. It discusses hashing as a technique to distribute dataset entries across an array of buckets using a hash function. It then describes various hashing techniques like separate chaining and open addressing to resolve collisions. Some applications discussed include how Dropbox uses hashing to check for copyrighted content sharing and how subtree caching is used in symbolic regression.
In this deck from the DOE CSGF Program Review meeting, Nicholas Frontiere from the University of Chicago presents: HACC - Fitting the Universe Inside a Supercomputer.
"In response to the plethora of data from current and future large-scale structure surveys of the universe, sophisticated simulations are required to obtain commensurate theoretical predictions. We have developed the Hardware/Hybrid Accelerated Cosmology Code (HACC), capable of sustained performance on powerful and architecturally diverse supercomputers to address this numerical challenge. We will investigate the numerical methods utilized to solve a problem that evolves trillions of particles, with a dynamic range of a million to one."
Watch the video: https://wp.me/p3RLHQ-i4l
Learn more: https://www.krellinst.org/csgf/conf/2017/
Sign up for our insideHPC Newsletter: http://insidehpc.com/newsletter
Strava Labs: Exploring a Billion Activity Dataset from Athletes with Apache S...Databricks
At Strava we have extensively leveraged Apache Spark to explore our data of over a billion activities, from tens of millions of athletes. This talk will be a survey of the more unique and exciting applications: A Global Heatmap gives a ~2 meter resolution density map of one billion runs, rides, and other activities consisting of three trillion GPS points from 17 billion miles of exercise data. The heatmap was rewritten from a non-scalable system into a highly scalable Spark job enabling great gains in speed, cost, and quality. Locally sensitive hashing for GPS traces was used to efficiently cluster 1 billion activities. Additional processes categorize and extract data from each cluster, such as names and statistics. Clustering gives an automated process to extract worldwide geographical patterns of athletes.
Applications include route discovery, recommendation systems, and detection of events and races. A coarse spatiotemporal index of all activity data is stored in Apache Cassandra. Spark streaming jobs maintain this index and compute all space-time intersections (“flybys”) of activities in this index. Intersecting activity pairs are then checked for spatiotemporal correlation, indicated by connected components in the graph of highly correlated pairs form “Group Activities”, creating a social graph of shared activities and workout partners. Data from several hundred thousand runners was used to build an improved model of the relationship between running difficulty and elevation gradient (Grade Adjusted Pace).
Cascading Map-Side Joins over HBase for Scalable Join ProcessingAlexander Schätzle
One of the major challenges in large-scale data processing with MapReduce is the smart computation of joins. Since Semantic Web datasets published in RDF have increased rapidly over the last few years, scalable join techniques become an important issue for SPARQL query processing as well.
In this paper, we introduce the Map-Side Index Nested Loop Join (MAPSIN join) which combines scalable indexing capabilities of NoSQL data stores like HBase, that suffer from an insufficient distributed processing layer, with MapReduce, which in turn does not provide appropriate storage structures for efficient large-scale join processing.
While retaining the flexibility of commonly used reduce-side joins, we leverage the effectiveness of map-side joins without any changes to the underlying framework. We demonstrate the significant benefits of MAPSIN joins for the processing of SPARQL basic graph patterns on large RDF datasets by an evaluation with the LUBM and SP2Bench benchmarks.
For selective queries, MAPSIN join based query execution outperforms reduce-side join based execution by an order of magnitude.
How to make hash functions go fast inside snarks, aka a guided tour through arithmetisation friendly hash functions (useful for all cryptographic protocols where cost is dominated by multiplications -- e.g. anything using R1CS; secret sharing based multiparty computation protocols; etc)
Basics of Distributed Systems - Distributed StorageNilesh Salpe
The document discusses distributed systems. It defines a distributed system as a collection of computers that appear as one computer to users. Key characteristics are that the computers operate concurrently but fail independently and do not share a global clock. Examples given are Amazon.com and Cassandra database. The document then discusses various aspects of distributed systems including distributed storage, computation, synchronization, consensus, messaging, load balancing and serialization.
Deep learning on a mixed cluster with deeplearning4j and sparkFrançois Garillot
Deep learning models can be distributed across a cluster to speed up training time and handle large datasets. Deeplearning4j is an open-source deep learning library for Java that runs on Spark, allowing models to be trained in a distributed fashion across a Spark cluster. Training a model involves distributing stochastic gradient descent (SGD) across nodes, with the key challenge being efficient all-reduce communication between nodes. Engineering high performance distributed training, such as with parameter servers, is important to reduce bottlenecks.
Mobility insights at Swisscom - Understanding collective mobility in SwitzerlandFrançois Garillot
Swisscom is the leading mobile-service provider in Switzerland, with a market share high enough to enable us to model and understand the collective mobility in every area of the country. To accomplish that, we built an urban planning tool that helps cities better manage their infrastructure based on data-based insights, produced with Apache Spark, YARN, Kafka and a good dose of machine learning. In this talk, we will explain how building such a tool involves mining a massive amount of raw data (1.5E9 records/day) to extract fine-grained mobility features from raw network traces. These features are obtained using different machine learning algorithms. For example, we built an algorithm that segments a trajectory into mobile and static periods and trained classifiers that enable us to distinguish between different means of transport. As we sketch the different algorithmic components, we will present our approach to continuously run and test them, which involves complex pipelines managed with Oozie and fuelled with ground truth data. Finally, we will delve into the streaming part of our analytics and see how network events allow Swisscom to understand the characteristics of the flow of people on roads and paths of interest. This requires making a link between network coverage information and geographical positioning in the space of milliseconds and using Spark streaming with libraries that were originally designed for batch processing. We will conclude on the advantages and pitfalls of Spark involved in running this kind of pipeline on a multi-tenant cluster. Audiences should come back from this talk with an overall picture of the use of Apache Spark and related components of its ecosystem in the field of trajectory mining.
These are the slides for the http://www.meetup.com/Big-Data-Romandie/events/230345605/
Most of the interesting bits are in the attached notebooks though :
https://gist.github.com/huitseeker/a868af0dd8064cfe9806f4974a955386
https://gist.github.com/huitseeker/3c6d1246178eea56d958a4757a8cadbd
To be used with :
https://github.com/andypetrella/spark-notebook
This document discusses ramping up DevOps for Big Data developers using Apache Mesos and Spark. It provides an overview of Mesos and its principles as a cluster manager and resource manager. It then discusses Spark and its advantages over Hadoop, including its speed, flexibility, and fault tolerance. The document also covers automating deployment of Mesos, HDFS and Spark using tools like Ansible, Packer and Tinc. It discusses ongoing work to further integrate Mesos and Spark.
A team of 4 data science PhDs worked with an organization's data for 3 weeks to answer a question. They used unsupervised clustering on web browsing history to identify new customer segments. Due to computational limitations, they implemented locality-sensitive hashing to cluster over 22 million nodes and 123 million edges representing customers' web browsing histories. On the last day, they obtained final results identifying singles as a customer segment, which aligned with existing marketing articles about the rise of singles as an economic segment. The key lessons were to lay a bare minimum pipeline first before refining, that distributed systems are difficult so focus on the problem, and that fuel and social support from colleagues are essential when tackling big challenges.
Cryptocurrency Exchange Script like Binance.pptxriyageorge2024
This SlideShare dives into the process of developing a crypto exchange platform like Binance, one of the world’s largest and most successful cryptocurrency exchanges.
Proactive Vulnerability Detection in Source Code Using Graph Neural Networks:...Ranjan Baisak
As software complexity grows, traditional static analysis tools struggle to detect vulnerabilities with both precision and context—often triggering high false positive rates and developer fatigue. This article explores how Graph Neural Networks (GNNs), when applied to source code representations like Abstract Syntax Trees (ASTs), Control Flow Graphs (CFGs), and Data Flow Graphs (DFGs), can revolutionize vulnerability detection. We break down how GNNs model code semantics more effectively than flat token sequences, and how techniques like attention mechanisms, hybrid graph construction, and feedback loops significantly reduce false positives. With insights from real-world datasets and recent research, this guide shows how to build more reliable, proactive, and interpretable vulnerability detection systems using GNNs.
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Wondershare Filmora is a video editing software and app designed for both beginners and experienced users. It's known for its user-friendly interface, drag-and-drop functionality, and a wide range of tools and features for creating and editing videos. Filmora is available on Windows, macOS, iOS (iPhone/iPad), and Android platforms.
Not So Common Memory Leaks in Java WebinarTier1 app
This SlideShare presentation is from our May webinar, “Not So Common Memory Leaks & How to Fix Them?”, where we explored lesser-known memory leak patterns in Java applications. Unlike typical leaks, subtle issues such as thread local misuse, inner class references, uncached collections, and misbehaving frameworks often go undetected and gradually degrade performance. This deck provides in-depth insights into identifying these hidden leaks using advanced heap analysis and profiling techniques, along with real-world case studies and practical solutions. Ideal for developers and performance engineers aiming to deepen their understanding of Java memory management and improve application stability.
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Avast Premium Security is a paid subscription service that provides comprehensive online security and privacy protection for multiple devices. It includes features like antivirus, firewall, ransomware protection, and website scanning, all designed to safeguard against a wide range of online threats, according to Avast.
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Join Ajay Sarpal and Miray Vu to learn about key Marketo Engage enhancements. Discover improved in-app Salesforce CRM connector statistics for easy monitoring of sync health and throughput. Explore new Salesforce CRM Synch Dashboards providing up-to-date insights into weekly activity usage, thresholds, and limits with drill-down capabilities. Learn about proactive notifications for both Salesforce CRM sync and product usage overages. Get an update on improved Salesforce CRM synch scale and reliability coming in Q2 2025.
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Why Orangescrum Is a Game Changer for Construction Companies in 2025Orangescrum
Orangescrum revolutionizes construction project management in 2025 with real-time collaboration, resource planning, task tracking, and workflow automation, boosting efficiency, transparency, and on-time project delivery.
Discover why Wi-Fi 7 is set to transform wireless networking and how Router Architects is leading the way with next-gen router designs built for speed, reliability, and innovation.
AgentExchange is Salesforce’s latest innovation, expanding upon the foundation of AppExchange by offering a centralized marketplace for AI-powered digital labor. Designed for Agentblazers, developers, and Salesforce admins, this platform enables the rapid development and deployment of AI agents across industries.
Email: [email protected]
Phone: +1(630) 349 2411
Website: https://www.fexle.com/blogs/agentexchange-an-ultimate-guide-for-salesforce-consultants-businesses/?utm_source=slideshare&utm_medium=pptNg
Creating Automated Tests with AI - Cory House - Applitools.pdfApplitools
In this fast-paced, example-driven session, Cory House shows how today’s AI tools make it easier than ever to create comprehensive automated tests. Full recording at https://applitools.info/5wv
See practical workflows using GitHub Copilot, ChatGPT, and Applitools Autonomous to generate and iterate on tests—even without a formal requirements doc.
How can one start with crypto wallet development.pptxlaravinson24
This presentation is a beginner-friendly guide to developing a crypto wallet from scratch. It covers essential concepts such as wallet types, blockchain integration, key management, and security best practices. Ideal for developers and tech enthusiasts looking to enter the world of Web3 and decentralized finance.
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DVDFab is a multimedia software suite primarily focused on DVD and Blu-ray disc processing. It offers tools for copying, ripping, creating, and editing DVDs and Blu-rays, as well as features for downloading videos from streaming sites. It also provides solutions for playing locally stored video files and converting audio and video formats.
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15. A WORD ON MODULARITY
LSH for EMD introduced by Charikar in the Simhash paper (2002).
Yet no place to plug your LSH family in implementation (e.g. scikit,
mrsqueeze) !
15
16. LSH AMPLIFICATION : CONCATENATIONS AND PARALLEL
▸ basic LSH:
▸ AND (series) construction:
▸ OR (parallel) construction :
16
18. BASIC LSH
val hashCollection = records.map(s => (getId(s), s)).
mapValues(s => getHash(s, hashers))
val subArray = hashCollection.flatMap {
case (recordId, hash) =>
hash.grouped(hashLength / numberBands).zipWithIndex.map{
case (band, bandIndex) => (bandIndex, (band, sentenceId))
}
}
18
19. LOOKUP
def findCandidates(record: Iterable[String], hashers: Array[Int => Int],
mBands: BandType) = {
val hash = getHash(record, hashers)
val subArrays = partitionArray(hash).zipWithIndex
subArrays.flatMap { case (band, bandIndex) =>
val hashedBucket = mBands.lookup(bandIndex).
headOption.
flatMap{_.get(band)}
hashedBucket
}.flatten.toSet
}
19
20. getHash(record,hashers)
DISTRIBUTE RANDOM SEEDS, NOT PERMUTATION FUNCTIONS
records.mapPartitions { iter =>
val rng = new Scala.util.random()
iter.map(x => hashers.flatMap{h => getHashFunction(rng, h)(x)})
}
20
22. BASIC LSH
WITH A 2-STABLE GAUSSIAN DISTRIBUTION
With data points, choose and
, to solve the problem
22
23. WEB LOGS ARE SPARSE
Input : hits per user, over 6 months, 2x50-ish integers/user (4GB)
Output of length 1000 integers per user : 10 (parallel) bands, 100
(concatenated) hashes
64-bit integers : 40 GB
Yet !
23
24. ENTROPY LSH (PANIGRAPHI 2006)
REPLACE TABLES BY OFFSETS
, , chosen randomly from the surface
of , the sphere of radius centered at
24
25. ENTROPY LSH
WITH A 2-STABLE GAUSSIAN DISTRIBUTION
With data points, choose and
, to solve the problem with as
few as hash tables
25
26. BUT ... NETWORK COSTS
▸ Basic LSH : look up buckets,
▸ Entropy LSH : search for offsets
26
27. LAYERED LSH (BAHMANI ET AL. 2012)
Output of your LSH family is in , with e.g. a cosine norm.
For closer points, the chance of hashes hashing to the same bucket is
high!
27
28. LAYERED LSH
Have an LSH family for your norm on
Likely that for all offsets
28
29. LAYERED LSH
Output of hash generation is (GH(p), (H(p), p)) for all p.
In Spark, group, or custom partitioner for (H(p), p) RDD.
Network cost :
29