Table Partitioning Basics for Performance and Maintenance
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The document provides an introduction to table partitioning in SQL Server. It explains what a partitioned table is, the key components like partition key, partition function, and partition scheme. It discusses why table partitioning is used, including benefits like partition elimination to improve query performance, ability to backup and restore partitions individually, and perform maintenance tasks like indexing and statistics updates on partitions. It also covers techniques like partition switching which allows fast loading and archiving of data without physically moving it. The document uses examples and diagrams to illustrate these concepts and components of table partitioning.
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Table Partitioning Basics for Performance and Maintenance
- 1. Table Partitioning in SQL Server A Magic Solution for Better Performance?
- 2. Cathrine Wilhelmsen @cathrinew cathrinewilhelmsen.net Data Warehouse Architect Business Intelligence Developer
- 3. You? New to table partitioning "Everything is slow" Today? Basic Introduction What, Why & How
- 4. A Magic Solution for Better Performance? Spoiler Alert!
- 5. A Magic Solution for Better Performance? Implementing table partitioning is not a trivial task and can actually cause worse performance...
- 6. A Magic Solution for Better Performance? ...but don't worry, I made plenty of mistakes so you can avoid them
- 8. What? Partition Key Partition Function Partition Scheme Why? Backup & Restore Maintenance Load & Archive How? Partition Elimination Switch, Split & Merge Sliding Windows
- 10. What is a partitioned table? 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... Data is physically stored in groups of rows called partitions Each partition can be accessed and maintained separately Partitioning is not visible to users, it behaves like one logical table
- 11. Partition Key 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... Data is partitioned based on a single column, the Partition Key The Partition Key should always be used as a filter in queries This ensures Partition Elimination: only relevant partitions are accessed
- 12. Partition Function 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... The Partition Function defines how to partition the data It specifies boundary values, the points between two partitions It specifies if the boundary value belongs to its left (upper) partition or its right (lower) partition
- 13. Partition Function: Range Left and Range Right 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ...
- 14. Partition Function: Range Left and Range Right Range Left means the boundary value is the last value in the left partition CREATE PARTITION FUNCTION pfLeft (INT) AS RANGE LEFT FOR VALUES (20,30,40); Range Right means the boundary value is the first value in the right partition CREATE PARTITION FUNCTION pfRight (INT) AS RANGE RIGHT FOR VALUES (20,30,40); ...20 21-30 41...31-40 ...19 20-39 40...30-39 20 30 40 20 30 40
- 15. Partition Scheme 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... The Partition Scheme maps logical partitions to physical filegroups Filegroups? Data files on one or more disks Backed up and restored individually Can be Read-Only
- 16. Map all partitions to one filegroup FILEGROUP 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ...
- 17. Map partitions to separate filegroups FILEGROUP1 (Read-Only) FILEGROUP2 (Read-Only) 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... FILEGROUP3 FILEGROUP4
- 18. How are partitions mapped to filegroups? ...20 21-30 41...31-40 ...19 20-39 40...30-39 20 30 40 20 30 40 The partition function specified the boundary values and partitions:
- 19. How are partitions mapped to filegroups? CREATE PARTITION SCHEME psLeft AS PARTITION pfLeft TO (FG1, FG2, FG3, FG4); CREATE PARTITION SCHEME psRight AS PARTITION pfRight TO (FG1, FG2, FG3, FG4); ...20 21-30 41...31-40 ...19 20-39 40...30-39 20 30 40 20 30 40 The partition scheme uses the partition function...
- 20. How are partitions mapped to filegroups? CREATE PARTITION SCHEME psLeft AS PARTITION pfLeft TO (FG1, FG2, FG3, FG4); CREATE PARTITION SCHEME psRight AS PARTITION pfRight TO (FG1, FG2, FG3, FG4); ...20 21-30 41...31-40 ...19 20-39 40...30-39 20 30 40 20 30 40 FG1 FG2 FG4FG3 FG1 FG2 FG4FG3 ...to map each partition to filegroups:
- 21. Filegroups Partition Scheme Partitioned Table 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... A partitioned table is created on a partition scheme instead of directly on a filegroup The partition scheme uses the partition key to store rows in the correct partition and filegroup based on the definition specified in the partition function
- 24. Partition Elimination SELECT COUNT(*) FROM Table WHERE Year = 2012; SELECT COUNT(*) FROM Table;
- 25. Partition Elimination SELECT COUNT(*) FROM Table WHERE Year = 2012; SELECT COUNT(*) FROM Table;
- 26. Backup & Restore Partitions Filegroups can be backed up and restored individually If each partition is mapped to a separate filegroup, partitions with the most critical data can be restored first
- 27. Backup & Restore Partitions Filegroups can be read-only If each partition is mapped to a separate filegroup, partitions with historical, unchanging data can be excluded from regular backups
- 28. Index Maintenance per Partition Rebuild and reorganize indexes per partition Rebuild indexes online per partition was introduced in SQL Server 2014 Set data compression per partition ALTER INDEX IndexName ON TableName REBUILD PARTITION = 2 WITH (ONLINE = ON);
- 29. Statistics Maintenance per Partition Update statistics on specific partitions instead of scanning and updating the whole table UPDATE STATISTICS TableName (StatisticsName) WITH RESAMPLE ON PARTITIONS (3,5); CREATE STATISTICS StatisticsName ON TableName (ColumnName) WITH INCREMENTAL = ON; Incremental Statistics was introduced in SQL Server 2014
- 30. Load & Archive: Partition Switching Partitions can be switched between tables, called switching in or switching out Partition switching is a metadata operation that updates the location of the data, no data is physically moved Extremely fast compared to inserting into or deleting from a large table 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... 2012-01-01 ... ... 2012-12-31 ... ... ALTER TABLE Table1 SWITCH PARTITION 5 TO Table2 PARTITION 5; SELECT $PARTITION.pf(2014);
- 31. Load & Archive: Switch out 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... Called switch out when you move data out of a table (archive)
- 32. Load & Archive: Switch out 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... 2012-01-01 ... ... 2012-12-31 ... ... Called switch out when you move data out of a table (archive)
- 33. Load & Archive: Switch in 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... 2016-01-01 ... ... 2016-12-31 ... ... Called switch in when you move data into a table (load)
- 34. Load & Archive: Switch in 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... 2016-01-01 ... ... 2016-12-31 ... ... Called switch in when you move data into a table (load)
- 35. Sliding Windows The Sliding Windows technique automates data loading, data archiving and partition management It keeps a certain number of partitions by continuously switching out the oldest data and switching in new data 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2012-01-01 ... ... 2012-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ...
- 36. Sliding Windows: Split & Merge 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... Partitions are not actually added or removed, they are split or merged Be careful! Splitting and merging partitions can cause data movement!!
- 37. Sliding Windows: Split & Merge 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... Split one partition in two by adding a new boundary value ALTER PARTITION FUNCTION pf () SPLIT RANGE ('2013-06-01'); Data movement will occur if there is data on both sides of the new boundary value!
- 38. Sliding Windows: Split & Merge 2012-01-01 ... ... 2012-12-31 ... ... 2013-01-01 ... ... 2013-12-31 ... ... 2014-01-01 ... ... 2014-12-31 ... ... 2015-01-01 ... ... 2015-12-31 ... ... Merge two partitions to one by removing a boundary value ALTER PARTITION FUNCTION pf () MERGE RANGE ('2014-01-01'); Data movement will occur if there is data on both sides of the old boundary value!
- 39. Sliding Windows Steps 1. Add new filegroup and file 2. Create switch out (archive) table 3. Create switch in (load) table and load it with new data 4. Split to add new partition 5. Switch in new partition 6. Switch out old partition 7. Merge to remove old partition 8. Delete switch out and switch in tables 9. Delete old file and filegroup
- 41. Alternative Sliding Windows Steps 1. Add new filegroup and file 2. Create switch out (archive) table 3. Switch out old partition 4. Merge to remove old partition 5. Create switch in (load) table and load it with new data 6. Split to add new partition 7. Switch in new partition 8. Delete switch out and switch in tables 9. Delete old file and filegroup
- 43. Case Study: What Went Wrong?
- 44. Background: Financial Data Warehouse Periodic Snapshot Fact Tables Daily, Weekly and Monthly Balances SQL Server, DB2, Oracle, .csv, .txt Loaded at different times during the day 1 2 3 4 5 6 7 Pension Insurance Bank Fund
- 45. First version Daily fact table: Keep 1 day per source 1 2 Pension 6 7 Bank Fund Monthly fact table: Keep 36 months per source 3 4 5 Insurance
- 46. Second version Daily fact table: Keep 1 day per source 1 2 Pension Monthly / Weekly fact table: Keep 36 months for some sources Keep 106 weeks for some sources 3 4 5 Insurance ! 6 7 Bank Fund
- 47. Third version Daily fact table: Keep 1 day per source 1 2 Pension Monthly / Weekly / Daily fact table: Keep 36 months for some sources Keep 106 weeks for some sources Keep 7 days for some sources 3 4 5 6 7 Insurance Bank Fund !!
- 50. Daily fact table partitioning 1 ... ... 2 ... ... 3 ... ... 4 ... ... 5 ... ... 6 ... ... 7 ... ... Partition Key: source number One partition per source Helped with deadlock issues Easy to switch data in and out
- 51. Monthly / Weekly / Daily fact table partitioning 12011 ... ... 12012 ... ... 12013 ... ... 12014 ... ... 19990 ... ... 19991 ... ... 19992 ... ... Partition Key: Source number + Period type Period type: YYYY for monthly data 9991 for weekly data 9992 for daily data Helped with deadlock issues, but…
- 52. Monthly / Weekly / Daily fact table partitioning 12011 ... ... 12012 ... ... 12013 ... ... 12014 ... ... 19990 ... ... 19991 ... ... 19992 ... ... Partition key was difficult to remember and was not used in queries Data had to be inserted into and deleted from partitions with existing data, instead of switching partitions in and out
- 53. What went wrong? "The usual suspects": Conflicting priorities, changing requirements and high pressure to deliver on time Fact tables were expanded, not changed, when new sources and requirements were implemented Partitioning was implemented on fact tables with multiple grains, instead of correcting the fact tables first
- 54. What did we learn?
- 55. test, test, test, test
- 56. References and Resources: Table Partitioning Brent Ozar Unlimited: SQL Server Table Partitioning Resources brentozar.com/sql/table-partitioning-resources/ Bradley Ball: Partitioning in SQL Server 2012 pragmaticworks.com/Training/FreeTraining/ViewWebinar/WebinarID/541
- 57. References and Resources: Further Reading Partial Backups in SQL Server 2014 msdn.microsoft.com/en-us/library/ms191539.aspx Piecemeal Restores in SQL Server 2014 msdn.microsoft.com/en-us/library/ms177425.aspx Benjamin Nevarez: SQL Server 2014 Incremental Statistics benjaminnevarez.com/2015/02/2014-incremental-statistics/