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SDIMS: A Scalable Distributed Information Management System

SDIMS: A Scalable Distributed Information Management System. Praveen Yalagandula Mike Dahlin Laboratory for Advanced Systems Research (LASR) University of Texas at Austin. Goal. A Distributed Operating System Backbone Information collection and management

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SDIMS: A Scalable Distributed Information Management System

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  1. SDIMS: A Scalable Distributed Information Management System Praveen Yalagandula Mike Dahlin Laboratory for Advanced Systems Research (LASR) University of Texas at Austin Department of Computer Sciences, UT Austin

  2. Goal • A Distributed Operating System Backbone • Information collection and management • Core functionality of large distributed systems • Monitor, query and react to changes in the system • Examples: • Benefits • Ease development of new services • Facilitate deployment • Avoid repetition of same task by different services • Optimize system performance System administration and management Service placement and location Sensor monitoring and control Distributed Denial-of-Service attack detection File location service Multicast tree construction Naming and request routing ………… Department of Computer Sciences, UT Austin

  3. Contributions – SDIMS • Provides an important basic building block • Information collection and management • Satisfies key requirements • Scalability • With both nodes and attributes • Leverage Distributed Hash Tables (DHT) • Flexibility • Enable applications to control the aggregation • Provide flexible API: install, update and probe • Autonomy • Enable administrators to control flow of information • Build Autonomous DHTs • Robustness • Handle failures gracefully • Perform re-aggregation upon failures • Lazy (by default) and On-demand (optional) Department of Computer Sciences, UT Austin

  4. Outline • SDIMS: a distributed operating system backbone • Aggregation abstraction • Our approach • Design • Prototype • Simulation and experimental results • Conclusions Department of Computer Sciences, UT Austin

  5. Aggregation Abstraction f(f(a,b), f(c,d)) Astrolabe [VanRenesse et al TOCS’03] 9 A2 • Attributes • Information at machines • Aggregation tree • Physical nodes are leaves • Each virtual node represents a logical group of nodes • Administrative domains, groups within domains, etc. • Aggregation function, f, for attribute A • Computes the aggregated value Ai for level-i subtree • A0 = locally stored value at the physical node or NULL • Ai = f(Ai-10, Ai-11, …, Ai-1k) for virtual node with k children • Each virtual node is simulated by one or more machines • Example: Total users logged in the system • Attribute: numUsers • Aggregation Function: Summation f(a,b) f(c,d) 4 5 A1 A0 d c 2 b 1 a 2 4 Department of Computer Sciences, UT Austin

  6. Outline • SDIMS: a distributed operating system backbone • Aggregation abstraction • Our approach • Design • Prototype • Simulation and experimental results • Conclusions Department of Computer Sciences, UT Austin

  7. Scalability with nodes and attributes • To be a basic building block, SDIMS should support • Large number of machines • Enterprise and global-scale services • Trend: Large number of small devices • Applications with a large number of attributes • Example: File location system • Each file is an attribute • Large number of attributes • Challenges: build aggregation trees in a scalable way • Build multiple trees • Single tree for all attributes  load imbalance • Ensure small number of children per node in the tree • Reduces maximum node stress Department of Computer Sciences, UT Austin

  8. Building aggregation trees: Exploit DHTs • A DHT can be viewed as multiple aggregation trees • Distributed Hash Tables (DHTs) • Each node assigned an ID from large space (160-bit) • For each prefix (k), each node has a link to another node • Matching k bits • Not matching on the k+1 bit • Each key from ID space mapped to a node with closest ID • Routing for a key: Bit correction • Example: from 0101 for key 1001 • 0101  1110  1000  1000  1001 • Lots of different algorithms with different properties • Pastry, Tapestry, CAN, CHORD, SkipNet, etc. • Load-balancing, robustness, etc. • A DHT can be viewed as a mesh of trees • Routes from all nodes to a particular key form a tree • Different trees for different keys Department of Computer Sciences, UT Austin

  9. DHT trees as aggregation trees • Key 111 111 11x 1xx 010 110 001 100 000 101 011 111 Department of Computer Sciences, UT Austin

  10. 000 111 00x 11x 0xx 1xx 010 010 110 110 001 001 100 100 000 000 101 101 011 011 111 111 DHT trees as aggregation trees • Keys 111 and 000 Department of Computer Sciences, UT Austin

  11. API – Design Goals • Expose scalable aggregation trees from DHT • Flexibility: Expose several aggregation mechanisms • Attributes with different read-to-write ratios • “CPU load” changes often: a write-dominated attribute • Aggregate on every write  too much communication cost • “NumCPUs” changes rarely: a read-dominated attribute • Aggregate on reads  unnecessary latency • Spatial and temporal heterogeneity • Non-uniform and changing read-to-write rates across tree • Example: a multicast session with changing membership • Support sparse attributes of same functionality efficiently • Examples: file location, multicast, etc. • Not all nodes are interested in all attributes Department of Computer Sciences, UT Austin

  12. Design of Flexible API • New abstraction: separate attribute type from attribute name • Attribute = (attribute type, attribute name) • Example: type=“fileLocation”, name=“fileFoo” • Install: an aggregation function for a type • Amortize installation cost across attributes of same type • Arguments up and down control aggregation on update • Update: the value of a particular attribute • Aggregation performed according to up and down • Aggregation along tree with key=hash(Attribute) • Probe: for an aggregated value at some level • If required, aggregation done to produce this result • Two modes: one-shot and continuous Department of Computer Sciences, UT Austin

  13. Scalability and Flexibility • Install time aggregation and propagation strategy • Applications can specify up and down • Examples • Update-Local up=0, down=0 • Update-All up=ALL, down=ALL • Update-Up up=ALL, down=0 • Spatial and temporal heterogeneity • Applications can exploit continuous mode in probe API • To propagate aggregate values to only interested nodes • With expiry time, to propagate for a fixed time • Also implies scalability with sparse attributes Department of Computer Sciences, UT Austin

  14. Scalability and Flexibility • Install time aggregation and propagation strategy • Applications can specify up and down • Examples • Update-Local up=0, down=0 • Update-All up=ALL, down=ALL • Update-Up up=ALL, down=0 • Spatial and temporal heterogeneity • Applications can exploit continuous mode in probe API • To propagate aggregate values to only interested nodes • With expiry time, to propagate for a fixed time • Also implies scalability with sparse attributes Department of Computer Sciences, UT Austin

  15. Scalability and Flexibility • Install time aggregation and propagation strategy • Applications can specify up and down • Examples • Update-Local up=0, down=0 • Update-All up=ALL, down=ALL • Update-Up up=ALL, down=0 • Spatial and temporal heterogeneity • Applications can exploit continuous mode in probe API • To propagate aggregate values to only interested nodes • With expiry time, to propagate for a fixed time • Also implies scalability with sparse attributes Department of Computer Sciences, UT Austin

  16. Scalability and Flexibility • Install time aggregation and propagation strategy • Applications can specify up and down • Examples • Update-Local up=0, down=0 • Update-All up=ALL, down=ALL • Update-Up up=ALL, down=0 • Spatial and temporal heterogeneity • Applications can exploit continuous mode in probe API • To propagate aggregate values to only interested nodes • With expiry time, to propagate for a fixed time • Also implies scalability with sparse attributes Department of Computer Sciences, UT Austin

  17. Scalability and Flexibility • Install time aggregation and propagation strategy • Applications can specify up and down • Examples • Update-Local up=0, down=0 • Update-All up=ALL, down=ALL • Update-Up up=ALL, down=0 • Spatial and temporal heterogeneity • Applications can exploit continuous modein probe API • To propagate aggregate values to only interested nodes • With expiry time, to propagate for a finite time • Also implies scalability with sparse attributes Department of Computer Sciences, UT Austin

  18. Autonomy • Systems spanning multiple administrative domains • Allow a domain administrator control information flow • Prevent external observer from observing the information in the domain • Prevent external failures from affecting the operations in the domain • Support for efficient domain wise aggregation • DHT trees might not conform • Autonomous DHT • Two properties • Path Locality • Path Convergence • Reach domain root first 111 110 101 100 000 010 001 011 Domain 2 Domain 1 Domain 3 Department of Computer Sciences, UT Austin

  19. Outline • SDIMS: a distributed operating system backbone • Aggregation abstraction • Our approach • Leverage Distributed Hash Tables • Separate attribute type from name • Flexible API • Prototype and evaluation • Conclusions Department of Computer Sciences, UT Austin

  20. Prototype and Evaluation • SDIMS prototype • Built on top of FreePastry [Druschel et al, Rice U.] • Two layers • Bottom: Autonomous DHT • Top: Aggregation Management Layer • Methodology • Simulation • Scalability • Flexibility • Prototype • Micro-benchmarks on real networks • PlanetLab • CS Department Department of Computer Sciences, UT Austin

  21. Simulation Results - Scalability • Methodology • Sparse attributes: multicast sessions with small size membership • Node Stress = Amt. of incoming and outgoing info • Two points • Max Node Stress an order of magnitude less than Astrolabe • Max Node Stress decreases as the number of nodes increases Astrolabe 65536 Astrolabe 4096 Astrolabe 256 SDIMS 256 SDIMS 4096 SDIMS 65536 Department of Computer Sciences, UT Austin

  22. Simulation Results - Flexibility • Simulation with 4096 nodes • Attributes with different up and down strategies Update-Local Update-All Up=5, down=0 Up=all, down=5 Update-Up Department of Computer Sciences, UT Austin

  23. Prototype Results • CS department: 180 machines (283 SDIMS nodes) • PlanetLab: 70 machines Department Network Planet Lab 800 3500 700 3000 600 2500 500 Latency (ms) 2000 400 1500 300 1000 200 500 100 0 0 Update - All Update - Up Update - Local Update - All Update - Up Update - Local Department of Computer Sciences, UT Austin

  24. Conclusions • SDIMS – basic building block for large-scale distributed services • Provides information collection and management • Our Approach • Scalability and Flexibility through • Leveraging DHTs • Separating attribute type from attribute name • Providing flexible API: install, update and probe • Autonomy through • Building Autonomous DHTs • Robustness through • Default lazy reaggregation • Optional on-demand reaggregation Department of Computer Sciences, UT Austin

  25. For more information: http://www.cs.utexas.edu/users/ypraveen/sdims Department of Computer Sciences, UT Austin

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