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Data & Backup Compression in SQL Server 2008

André Kamman Friday November 20 th @ SQLBITS IV. Data & Backup Compression in SQL Server 2008. About Me. André Kamman > 20 years in IT Main focus on complex SQL Server environments (or a whole lot of less complex ones) Co-founder, current chairman of Dutch PASS Chapter (sqlpass.nl)

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Data & Backup Compression in SQL Server 2008

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  1. André Kamman Friday November 20th @ SQLBITS IV Data & Backup Compressionin SQL Server 2008

  2. About Me • André Kamman • > 20 years in IT • Main focus on complex SQL Server environments (or a whole lot of less complex ones) • Co-founder, current chairman of Dutch PASS Chapter (sqlpass.nl) • Organizing Committee for the PASS European Conference

  3. Agenda • Why compress ? • Backup Compression • Data Compression • Row, Page, Unicode (R2) • How to choose • How to implement • Maintainability

  4. Why Compress ? • Disk throughput (a lot) slower than memory and CPU • David DeWitt keynote at PASS Summit : • Since 1985 CPU x 1000 faster • Since 1985 Disk x 65 (!) faster • Much larger capacity for disks but bandwith and seek times not so much result in a 150 x relatively slower disk. • Need less disk space

  5. Backup Compression • Enterprise & Developer Edition only • Can restore to Standard Edition • Also in Standard Edition starting at R2 ! • Closest to the data, generally better than compressing when copying or deduping on the san for instance. • Lots of competition from Quest, Redgate, Idera, Hyperbac, etc. • Still adds value after implementing Data Compression

  6. Row Compression • Stores fixed length types as variable length. (with improved overhead) • i.e.: int (4 bytes) can be stored in 1 byte if the value is low enough • Makes vardecimal obsolete. Can still be used but is deprecated.

  7. Good to know • Compression also in memory • Implications on replication • Transaction log, Version store and Non-leaf pages stored row compressed only • Can’t restore to standard edition • Fix : KB963658 Compression is removed after shrink • Don’t shrink ! Or at least mind the fragmentation !

  8. Page Compression Pre-Fix Dictionary Page Header aaabb aaaab abcd 0 4b 0 4b 1 0bbbb aaabcc bbbb abcd 3ccc 1 0bbbb aaaccc aaaacc bbbb

  9. Unicode Compression in SQL Server 2008 R2 • SCSU Simple Compression Scheme for Unicode Data • Uses 1 byte instead of 2 when it can.

  10. How to Choose - Effectiveness • Good Compression • Numeric or fixed length character fields that don’t use all the allocated bytes • Repeating data or prefix values • Poor or no Compression • Fields using up all the allocated bytes • Not much repeated data • Repeated with non-repeating prefixes • Out of row data • FILESTREAM data

  11. How to choose • sp_estimate_data_compression_savings • Quick Rule of thumb : • ROW is lowcost, generally 10% CPU overhead. Use it on everything on OLTP • PAGE is more expensive, but compresses more. Us it on everything on DWH • Analyze Workload Characteristics(to help decide on Page Compression candidates)

  12. Example of decision matrix

  13. How to Implement • Table, Index, Partition • Create, alter …rebuild • Can only set ROW or PAGE • Mind tempspace, cpu etc. This is just like an Index Rebuild • Mind cpu even more with ONLINE option

  14. Some code examples

  15. CREATE TABLE T1 (c1 int, c2 nvarchar(50) ) WITH (DATA_COMPRESSION = ROW) CREATE TABLE PartitionTable1 (col1 int, col2 varchar(max)) ON myRangePS1 (col1) WITH ( DATA_COMPRESSION = ROW ON PARTITIONS (1), DATA_COMPRESSION = PAGE ON PARTITIONS (2 TO 4) ); GO

  16. ALTER TABLE T1 REBUILD WITH (DATA_COMPRESSION = PAGE); GO ALTER TABLE PartitionTable1 REBUILD PARTITION = ALL WITH (DATA_COMPRESSION = PAGE ON PARTITIONS(1) ) ; GO ALTER TABLE PartitionTable1 REBUILD PARTITION = ALL WITH ( DATA_COMPRESSION = PAGE ON PARTITIONS(1), DATA_COMPRESSION = ROW ON PARTITIONS(2 TO 4) ) ; GO

  17. ALTER INDEX IX_INDEX_1 ON T1 REBUILD WITH ( DATA_COMPRESSION = PAGE ) ; GO ALTER INDEX IX_PartTab2Col1 ON PartitionTable1 REBUILD PARTITION = ALL WITH ( DATA_COMPRESSION = PAGE ON PARTITIONS(1), DATA_COMPRESSION = ROW ON PARTITIONS(2 TO 4) ) ; GO

  18. Maintainability - Monitor • Perfmon • Page compression attempts/sec • Pages compressed/sec(SQL Server, Access Methods object) • Sys.dm_db_index_operational_stats • Sys.dm_db_persisted_sku_features • Sys.partitions(column data_compression_desc)

  19. Maintenance • HeapPages are only compressed when bulk inserted, inserted with tablock or rebuild • Table with clustered indexPages are compressed when page is full. (before page split is attempted)

  20. Quiz

  21. Questions ?

  22. Contact me : • Email : andre@sqlserverdba.nl • Twitter : @AndreKamman • Blog : http://andrekamman.com • This presentation : • http://andrekamman.com/presentations • Or just stop me when you run into me

  23. Thank you ! Don’t forget to fill out the evals please !

  24. Links / Resources • SQLCAT.com whitepaper : • http://sqlcat.com/whitepapers/archive/2009/05/29/data-compression-strategy-capacity-planning-and-best-practices.aspx(Couple of very useful links to blogs etc. inside this whitepaper!) • Storage Engine Team Blog on Compression : • http://blogs.msdn.com/sqlserverstorageengine/archive/tags/Data+Compression/default.aspx • Don’t shrink : • http://www.sqlskills.com/BLOGS/PAUL/post/Auto-shrink-e28093-turn-it-OFF!.aspx • http://www.sqlskills.com/BLOGS/PAUL/post/Why-you-should-not-shrink-your-data-files.aspx

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