Stored procedure wrapper for Java & PGObserver

1. Stored procedure wrapper for Java & PGObserver Jan Mussler | PGConf.EU 2012

2. Outline ● Introduction ● Stored procedure wrapper ● – Problems before the wrapper – How it works – How to use it – More features including sharding PGObserver

3. Zalando ● ● ● ● 14 countries 471 Mio € revenue 1st half of 2012 3 warehouses Europe's largest online fashion retailer tech.zalando.org 3

4. Zalando platform ● ● ● ● Modern open source software stack Mostly Java PostgreSQL database backend > 150 developers tech.zalando.org 4

5. PostgreSQL setup ● ~ 20+ Servers PostgreSQL master servers ● ~ 4.000 GB of data ● Started with PostgreSQL 9.0 rc1 ● Now running version 9.0 to 9.2 ● – cascading replication very welcome – maintenance improvements great ( drop concurrently ) – Index only scan, pg_stat_statement improvements Machine setup – 8- to 48- cores, 16GB to 128GB – SAN, no SAN with ( 2x2x RAID 1, 4x RAID 10 ) preferred 5

6. PostgreSQL availability ● BoneCP as Java connection pool ● All databases use streaming replication – ● Failover is manual task – ● Service IP for switching Monitored by Jave app, Web frontend Significant replication delays sometimes – Fullpage writes, Nested Transactions, Slave load 6

7. Stored procedure experience ● Performance benefits ● Easy to change live behavior ● Makes moving to new software version easy ● Validation close to data ● Run a very simplistic transaction scope ● Cross language API layer ● More than 1000 stored procedures – More plpgsql than SQL than plpython 7

8. Outline ● Introduction ● Stored procedure wrapper ● – Problems before the wrapper – How it works – How to use it – More features including sharding PGObserver

9. Execution of stored procedures ● ● Using spring's BaseStoredProcudere – Initially a lot of work per stored procedure – One class per stored procedure – Write row mappers for domain object mapping Missing type mapper on Java side – Spring type mapper insufficient ● ● Enums, array of types, nesting, and hstore missing JdbcTemplate or alternatives lack ease of use 9

10. Goals of our wrapper ● Write as little code as possible on Java side ● One location for procedures of same topic ● One call path to any stored procedure ● “Natural” feeling for using stored procedures – Procedure call should look like Java method call – RPC like 10

11. Brief example 11

12. Brief example 12

13. Brief example 13

14. Outline ● Introduction ● Stored procedure wrapper ● – Problems before the wrapper – How it works – How to use it – More features including sharding PGObserver

15. Under the hood Service Object Invoke method() Proxy Object StoredProcudure lookup StoredProcedure Object Datasource Provider Typemapper Datasource JDBC Connection 15

16. Features ● ● New spring compatible type mapper – From simple types to nested domain objects – Supports PG enum to Java enum Accessing sharded data supported – Result “aggregation” across shards – Parallel query issuing ● Advisory locking via annotation ● Set custom timeout per stored procedure 16

17. Type mapper ● Annotations for class and member variables – @DatabaseType and @DatabaseField ● CamelCase to camel_case conversion ● JPA 2.0 @Column annotation supported ● Addition type conversions include: – Nested PostgreSQL types to Java objects – hstore to Map<String,String> – PostgreSQL enum to Java enum ( by name ) – PostgreSQL array[] to List<?>() 18

18. Outline ● Introduction ● Stored procedure wrapper ● – Problems before the wrapper – How it works – How to use it – More features including sharding PGObserver

19. Using the wrapper ● Considere Java to PostgreSQL plpgsql ● First define the Java interface 21

20. Using the wrapper ● Create class implementing previous interface 22

21. Using the wrapper ● Define DTO classes if necessary – Input parameters – ResultSet mapping 23

22. Using the wrapper ● Next create analogous PostgreSQL types CREATE TYPE t_customer AS ( id int, name text, address t_address[] ); ● Or use “OUT” columns CREATE FUNCTION load_customer( INOUT id int, OUT name text, OUT address t_address[] ) RETURNS SETOF record AS ● Implement stored procedures 24

23. Putting it together ● Integration test 25

24. Outline ● Introduction ● Stored procedure wrapper ● – Problems before the wrapper – How it works – How to use it – More features including sharding PGObserver

25. Running SQL queries ● @SProcCall(sql=”[...]”) may run any query – Benefit from type mapper – Relatively easy to use – Although mixing SQL into Java source @SProcCall(sql=”UPDATE t SET name = ?” + “ WHERE id = ? ” + “ RETURNING id”) int updateName(@SProcParam String newName, @SProcParam int userId); // allows you then to do: int r = service.updateName('Jan',1001); 27

26. Sharding support ● Parameter annotation @ShardKey ● @ShardKey and @SProcParam may overlap @SProcCall Customer getCustomer(@ShardKey int shardId, @SProcParam String cnumber) @SProcCall Article getArticle(@ShardKey @SProcParam ean) ● ShardedObject interface for custom classes ● Added datasource providers for translation 28

27. Different datasource providers Article ShardedObject EAN Key EAN123 MD5 ShardKey Strategy [...]10 Bitmap DataSource Provider 01 Java code and annotations 11 *0 DataSource DataSource DataSource Spring context config 29

28. Search and “Merge” result set search() Shard 1 ResultSet Thread 1 Wrapper Shard 2 ● ResultSet Thread 2 Use searchShards where you do not know the shard – ● search() List<Result> will run on all shards return on first find Use runOnAllShards execute on all shards – Search name like 'Na%' and return one collection 30

29. Auto partitioning Shard Strategy Set 1 (13 char) Shard 1 Set 2 (13 char) Shard 2 Set of EANs (13 char) ● ● Java method called with one large collection – Wrapper will split collection according to key – Execute SQL for split collection on each shard Default behavior if @ShardKey is a collection 31

30. Java bean validation ● Annotation based validation ( JSR 303 ) ● Relying on hibernate validator ● Automatically checked inside wrapper – Less boiler plate code – @SProcService(validate = true) 32

31. Value transformers ● ● Global registry for type conversions – e.g. for use with JodaTime class – Enables transparent handling of legacy types Usefull for ::text to Java class conversion – Type safe domain classes – ::text => class EAN 33

32. Per stored procedure timeout ● Trouble with global statement timeout – ● Long running queries and supposedly fast ones Added @SProcCall(timeout=x) – X is timeout in ms – Allows overwrite for long running jobs – Ensures limited run time for “fast” functions ● Search functions with too few constraints 34

33. Concurrency with advisory locks ● Single database serves many Java instances – ● Synchronization may be required Wrapper features one enum for different locks – @SProcCall(advisoryLockType=LOCK1) – Easy locking – One enum warns developers of existing locks 35

34. Transaction support ● ● ● Spring's @Transactional should work – More or less datasource dependent – Sharded environment more complicated For multi shard operations wrapper provides – Context is one procedure equals one transaction – Immediate commit on each shard – Commit only if all executions were successful – Use two phase commit Enabled on SProcService or SProcCall level 36

35. Outline ● Introduction ● Stored procedure wrapper ● – Problems before the wrapper – How it works – How to use it – More features including sharding PGObserver

36. PGObserver ● ● Build to monitor PostgreSQL performance – Stored procedures as execution unit – Track table statistics to assist identifying causes Infrastructure – One Java data gatherer – Web frontend in using Python – Metric data is stored in PostgreSQL – Per service configuration of all gather intervals 38

37. PGObserver database view 39

38. PGObserver database view CPU vs Sproc Load IO related stats Top 10 by runtime Top 10 by calls 40

39. Sequential scan in live env. Total runtime per monitored 15min Avg. run time per call Avg. self time per call 41

40. Table I/O data excerpt Table size Index size Sequential scans 42

41. Summary ● Stored procedures can improve performance ● Type mapper great library to reduce map code ● Wrapper makes procedure usage a lot easier ● ● Stored procedure and general PostgreSQL performance monitoring is very important Wrapper and PGObserver available soon! Visit us on:  http://www.github.com/zalando  http://tech.zalando.org 43

42. Thank you for listening Jan Mussler | PGConf.EU 2012 44