Custom Pregel Algorithms in ArangoDB
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These are the slides to the webinar about Custom Pregel algorithms in ArangoDB https://youtu.be/DWJ-nWUxsO8. It provides a brief introduction to the capabilities and use cases for Pregel.
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Custom Pregel Algorithms in ArangoDB
- 1. Feature Preview: Custom Pregel Complex Graph Algorithms made Easy @arangodb @joerg_schad @hkernbach
- 2. 2 tl;dr ● “Many practical computing problems concern large graphs.” ● ArangoDB is a “Beyond Graph Database” supporting multiple data models around a scalable graph foundation ● Pregel is a framework for distributed graph processing ○ ArangoDB supports predefined Prgel algorithms, e.g. PageRank, Single-Source Shortest Path and Connected components. ● Programmable Pregel Algorithms (PPA) allows adding/modifying algorithms on the flight Disclaimer This is an experimental feature and especially the language specification (front-end) is still under development!
- 3. Jörg Schad, PhD Head of Engineering and ML @ArangoDB ● Suki.ai ● Mesosphere ● Architect @SAP Hana ● PhD Distributed DB Systems ● Twitter: @joerg_schad
- 4. 4 Heiko Kernbach Core Engineer (Graphs Team) @ ● Graph ● Custom Pregel ● Geo / UI ● Twitter: @hkernbach ● Slack: hkernbach.ArangoDB
- 5. 5 ● Open Source ● Beyond Graph Database ○ Stores, K/V, Documents connected by scalable Graph Processing ● Scalable ○ Distributed Graphs ● AQL - SQL-like multi-model query language ● ACID Transactions including Multi Collection Transactions
- 7. https://blog.acolyer.org/2015/05/26/pregel-a-system-for-large-scale-graph-processing/ Pregel Max Value While not converged: Communicate: send own value to neighbours Compute: Own value = Max Value from all messages (+ own value) Superstep
- 8. ArangoDB and Pregel: Status Quo ● https://www.arangodb.com/docs/stable/graphs-pregel.html ● https://www.arangodb.com/pregel-community-detection/ Available Algorithms ● Page Rank ● Seeded PageRank ● Single-Source Shortest Path ● Connected Components ○ Component ○ WeaklyConnected ○ StronglyConnected ● Hyperlink-Induced Topic Search (HITS)Permalink ● Vertex Centrality ● Effective Closeness ● LineRank ● Label Propagation ● Speaker-Listener Label Propagation 8 var pregel = require("@arangodb/pregel"); pregel.start("pagerank", "graphname", {maxGSS: 100, threshold: 0.00000001, resultField: "rank"}) ● Pregel support since 2014 ● Predefined algorithms ○ Could be extended via C++ ● Same platform used for PPA Challenges Add and modify Algorithms
- 9. Programmable Pregel Algorithms (PPA) const pregel = require("@arangodb/pregel"); let pregelID = pregel.start("air", graphName, "<custom-algorithm>"); var status = pregel.status(pregelID); ● Add/Modify algorithms on-the-fly ○ Without C++ code ○ Without restarting the Database ● Efficiency (as Pregel) depends on Sharding ○ Smart Graphs ○ Required: Collocation of vertices and edges 9
- 10. Custom Algorithm 10 { "resultField": "<string>", "maxGSS": "<number>", "dataAccess": { "writeVertex": "<program>", "readVertex": "<array>", "readEdge": "<array>" }, "vertexAccumulators": "<object>", "globalAccumulators": "<object>", "customAccumulators": "<object>", "phases": "<array>" } Accumulators Accumulators are used to consume and process messages which are being sent to them during the computational phase (initProgram, updateProgram, onPreStep, onPostStep) of a superstep. After a superstep is done, all messages will be processed. ● max: stores the maximum of all messages received. ● min: stores the minimum of all messages received. ● sum: sums up all messages received. ● and: computes and on all messages received. ● or: computes or and all messages received. ● store: holds the last received value (non-deterministic). ● list: stores all received values in list (order is non-deterministic). ● custom
- 11. Custom Algorithm 11 { "resultField": "<string>", "maxGSS": "<number>", "dataAccess": { "writeVertex": "<program>", "readVertex": "<array>", "readEdge": "<array>" }, "vertexAccumulators": "<object>", "globalAccumulators": "<object>", "customAccumulators": "<object>", "phases": "<array>" } ● resultField (string, optional): Name of the document attribute to store the result in. The vertex computation results will be in all vertices pointing to the given attribute. ● maxGSS (number, required): The max amount of global supersteps After the amount of max defined supersteps is reached, the Pregel execution will stop. ● dataAccess (object, optional): Allows to define writeVertex, readVertex and readEdge. ○ writeVertex: A program that is used to write the results into vertices. If writeVertex is used, the resultField will be ignored. ○ readVertex: An array that consists of strings and/or additional arrays (that represents a path). ■ string: Represents a single attribute at the top level. ■ array of strings: Represents a nested path ○ readEdge: An array that consists of strings and/or additional arrays (that represents a path). ■ string: Represents a single path at the top level which is not nested. ■ array of strings: Represents a nested path ● vertexAccumulators (object, optional): Definition of all used vertex accumulators. ● globalAccumulators (object, optional): Definition all used global accumulators. Global Accumulators are able to access variables at shared global level. ● customAccumulators (object, optional): Definition of all used custom accumulators. ● phases (array): Array of a single or multiple phase definitions. ● debug (optional): See Debugging.
- 12. Phases - Execution order 12 Step 1: Initialization 1. onPreStep (Conductor, executed on Coordinator instances) 2. initProgram (Worker, executed on DB-Server instances) 3. onPostStep (Conductor) Step {2, ...n} Computation 1. onPreStep (Conductor) 2. updateProgram (Worker) 3. onPostStep (Conductor)
- 13. Program - Arango Intermediate Representation (AIR) 13
- 14. Program - Arango Intermediate Representation (AIR) Lisp-like intermediate representation, represented in JSON and supports its data types 14 Specification ● Language Primitives ○ Basic Algebraic Operators ○ Logical operators ○ Comparison operators ○ Lists ○ Sort ○ Dicts ○ Lambdas ○ Reduce ○ Utilities ○ Functional ○ Variables ○ Debug operators ● Math Library ● Special Form ○ let statement ○ seq statement ○ if statement ○ match statement ○ for-each statement ○ quote and quote-splice statements ○ quasi-quote, unquote and unquote-splice statements ○ cons statement ○ and and or statements
- 15. Program - Arango Intermediate Representation (AIR) Lisp-like intermediate representation, represented in JSON and supports its data types 15 Specification ● Language Primitives ○ Basic Algebraic Operators ○ Logical operators ○ Comparison operators ○ Lists ○ Sort ○ Dicts ○ Lambdas ○ Reduce ○ Utilities ○ Functional ○ Variables ○ Debug operators ● Math Library ● Special Form ○ let statement ○ seq statement ○ if statement ○ match statement ○ for-each statement ○ quote and quote-splice statements ○ quasi-quote, unquote and unquote-splice statements ○ cons statement ○ and and or statements
- 16. Pregelator Simple Foxx service based IDE 16https://github.com/arangodb-foxx/pregelator
- 18. PPA: What is next? - Gather Feedback - In particular use-cases - Missing functions & functionality - User-friendly Front-End language - Improve Scale/Performance of underlying Pregel platform - Algorithm library - Blog Post (including Jupyter example) 18 ArangoDB 3.8 (end of year) - Experimental Feature - Initial Library ArangoDB 3.9 (Q1 21) - Draft for Front-End - Extended Library - Platform Improvements ArangoDB 4.0 (Mid 21) - GA
- 19. Pregel vs AQL When to (not) use Pregel… - Can the algorithm be efficiently be expressed in Pregel? - Counter example: Topological Sort - Is the graph size worth the loading? 19 AQL Pregel All Models (Graph, Document, Key-Value, Search, …) Iterative Graph Processing Online Queries Large Graphs, multiple iterations
- 20. How can I start? ● Docker Image: arangodb/enterprise-preview:3.8.0-milestone.3 ● Check existing algorithms ● Preview documentation ● Give Feedback ○ https://slack.arangodb.com/ -> custom-pregel 20
- 21. Thanks for listening! 21 Reach out with Feedback/Questions! • @arangodb • https://www.arangodb.com/ • docker pull arangodb Test-drive Oasis 14-days for free