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JSSUG: SQL Sever Performance Tuning
- 1. Microsoft SQL Server PerformanceTuning Kenichiro Nakamura
- 2. 16 MCPs forSQL 70-765 70-764 70-762 70-761 70-473 70-463 70-465 70-464 70-462 70-451 70-433 70-442 70-441 70-447 70-229 70-228 BI….??? Best tuning 5 mins query -> 0.02 sec.
- 3. What you willlearn today No details of SQL architecture No details of index tuning No details of SQLOS How to think about everything from performance point of view.
- 4. Take away (1/2) Allperformance issue has reasons. Understand where the issue comes from. (CPU, Memory, Disk) All performance features are: • solve the bottle neck somehow • workaround the bottle neck It may generate another issue
- 5. Take away (2/2) Newfeatures may: Improve performance and/or Decrease performance
- 6. Goal Let you feelyou learn something Demystify performance turning myth And confuse you all
- 7. What is performance? •Latency • Throughput • Best vs Optimized performance
- 8. What are bottlenecks? CPU RAM Disk(HDD/SSD) Network Developer Admin
- 9. What are bottlenecks CPU– Speed, Cores (NUMA) RAM – Speed, Size (NUMA) Disk (HDD/SSD) – Speed Size Network – Speed Developer – Poor Query Admin – Poor maintenance
- 10. How SQL storesdata IO matters
- 11. Question Which cluster sizeis optimal for SQL Server? • 4KB • 8KB • 16KB • 32KB • 64KB • 128KB
- 12. Question Fill factor shouldbe: • 0 • 50 • 70 • 100
- 13. Question Which data canbe stay together? • Data, Log, TempDB all together • Data, TempDB together • Everything separate
- 14. Page 1 page =8KB = 8192 byte Header = 96 bytes • Page ID • Next Page Pointer • Space • Row # Data = 8060 bytes https://msdn.microsoft.com/en-US/library/ms143432(SQL.120).aspx
- 15. Extend 1 Extend =8 Pages = 64KB Mixed extent Uniform extend https://docs.microsoft.com/en-us/sql/relational-databases/pages-and-extents-architecture-guide?view=sql-server-2017
- 16. GAM, SGAM andPFS GAM Record what extents have been allocated. SGAM Record which extents are used as mixed extents and have unused page. Each GAM/SGAM covers 64,000 extents, or almost 4 GB of data. PFS (Page Free Space) Record the allocation status of each page. Check if its empty, 1 to 50 percent full, 51 to 80 percent full, 81 to 95 percent full, or 96 to 100 percent full.
- 17. (IAM) Index AllocationMap Maps the extents in a 4-gigabyte (GB) part of a database file used by an allocation unit. • IN_ROW_DATA Holds a partition of a heap or index. • LOB_DATA Holds large object (LOB) data types, such as xml, varbinary(max), and varchar(max). • ROW_OVERFLOW_DATA Holds variable length data stored in varchar, nvarchar, varbinary, or sql_variant columns that exceed the 8,060 byte row size limit.
- 18. Data and Log Howthey store data? Data : Random Access RAID 10/5 Log: Sequential and writes only for normal time RAID 0
- 19. Fill factor Avoid Pagesplit but why? May place pages into different extent => More IO Split happens when data is inserted in the middle Log? Sequential Guid?
- 20. Compression CPU usage vsIO Backup Columnstore Pages When to compress data?
- 21. Encryption Performance vs Security TDE AlwaysEncrypted Column Encryption Data Masking No encryption but meet security requirement CPU resource
- 22. Partitioning and Stretchdatabase Want to reduce Partitioning Avoid query unnecessary partitions Move old data to other table Stretch Remove data from local by move old data to Azure Archive?? Cannot query
- 23. Question What happens whendata or log file out of space? • SQL stops • Auto grow the space • Archive old data
- 24. File space management Autogrow settings Cause many issues, last resort Instant File Initialization Not for transaction log TempDB?
- 25.
- 26. Question SQL server neveruse memory more than “max server memory” settings value. • Yes • No
- 27. Question What kind ofobject cached in memory? • You name it.
- 28. Question When SQL serverrereleases a cached object from its memory? • When no one uses the cached data anymore • It won’t release no matter what • Only when needed under memory pressure
- 29. Question SQL requires diskaccess for query execution. • True • False
- 30. How fast SSDvs. DDR4 SSD • Sequential Read/Write 3,100/2,000MB/s • Random Read/Write 540K/50K IOPs (2160/200MB/s) DDR4 • Transfer rate 3200 Mb/s (25.6GB/s)
- 31. Max and minserver memory 1. Start from less then min. 2. Keep acquiring memory until it exceeds min. 3. Not exceed max. 4. When releases memory, it still keeps min memory. https://docs.microsoft.com/en-us/sql/relational-databases/memory-management-architecture-guide?view=sql-server- 2017
- 32. Buffer Management 1 buffer= 8KB page. NUMA support DISK/IO SQL reads and writes to buffer, not disk. => Read ahead to improve performance => Lazy writer writes data to disk (or checkpoint) https://docs.microsoft.com/en-us/sql/relational-databases/memory-management-architecture-guide?view=sql-server- 2017#buffer-management
- 33. Buffer Management ReadData Read ahead Read 64 pages (512 KB) (SQL2016) Read up to with dynamic algorithm 4 MB data (SQL2017) sequential read-ahead random prefetching read-ahead https://www.sqlshack.com/sql-server-read-ahead-mechanism-concept-performance-gains/
- 34. Buffer Management WriteData https://docs.microsoft.com/en-us/sql/relational-databases/writing-pages?view=sql-server-2017
- 35. Query Execution and Performance Howto run query?
- 36. Question Query Optimizer generatesthe best execution plan. • Of course! • Not really.
- 37. Question Why optimizer cancreate plan before execute query? • By gut • By query records first • By using stats • It does optimize by last ran result
- 38. Question Why optimizer generatesquery plan? • Every time • When query looks complex • When no plan cached
- 39. Question MDOP should besame as CPU core numbers? • Yes • Even more! • 50% of cores • 1
- 40. Question SQL Server requiresIO all the time regardless logical/physical • Yes • No
- 41.
- 42. Additional cost Join Trigger Audit Log Index management(except select) TempDB Update Statistics
- 43. Parallelism Good for querylatency Not necessary good for throughput How to decide?
- 44. Question Index boost queryperformance • Of course! • Only select • Only select and update • It depends…
- 45. Heap, Clustered Index,Non-clustered Index Heap : Table Ordered as inserted Clustered Index : Table B-tree Ordered by specified column(s) value Non-clustered Index : Additional data
- 46. More indexes Unique Index FilteredIndex Covering Index Columnstore Index
- 47. Statistics Auto (Default) Manual Used byQuery Optimizer
- 48. Index fragmentation For optimizeIO and continuity Fill factor Reorganize Rebuild Online/Offline – What is offline?
- 49. Question Why SQL Serveris slow? • Because it’s Microsoft product! • Because it’s not Oracle nor MySQL no PostgreSQL!! • Due to ACID
- 50. Question How to archiveACID? • By lock • By latch • By magic
- 51. Question What kind of“wait” may happen during query execution? • You name it.
- 52. Question Snapshot should beon as there are no drawbacks! Even Azure SQL does it. • Yes • No
- 53. Lock variation Lock mode Shared Update Exclusive Intent Schema BU KeyRange https://docs.microsoft.com/en-us/sql/relational-databases/sql-server-transaction-locking-and-row-versioning- guide?view=sql-server-2017
- 54. Isolation Isolation Read Uncommitted Read Committed- default Repeatable Read Snapshot - default Serializable https://docs.microsoft.com/en-us/sql/connect/jdbc/understanding-isolation-levels?view=sql-server-2017
- 55.
- 56. Question Temp DB isevil • Yes • Sure!! • Absolutely!!!! • Not really Too much topics to cover.
- 57. SQL Server 2017 NewFeatures
- 58. Performance related newfeatures Resumable online index rebuild New adaptive queries Auto tuning 256 GB initial tempdb file size Computed columns, json functions, cross apply for in-memory optimized tables Read Scalability Group (wo/cluster) New read ahead algorithm Query Store enhancement (wait statistics) https://www.youtube.com/watch?v=DK4xUzG4Zm0
- 59. Best Practices Index, partition,statistics Procedures and parameterized queries Max server memory and mdop Multiple files for tempdb Avoid auto grow SnapshotLock pages IFI Power Settings Location of data and log files In-memory table Columnstore index Use persisted memory
- 60.
- 61.