DBMSPerformance Tuning

DBMS Architecture

Shared Memory

Databases

locks

log fileWork Areas

GCF

SCF

PSF OPF QEF

RDF QSF ADF

SXF GWF

DMF

RecoveryServer

logbuffers

DBMS Servers

Manages client access to databases Comprises functionality specific facilities By default one per installation Multi-threaded process Has system threads and user threads Configurable

Agenda

Disk– Location layout

CPU– Threads

Memory– Caches

Disk

Locations Tables Pages

Locations

Names by which Ingres points to a disk area At installation default locations are set up for

– Database – Journal– Dump– Checkpoint– Work

Use locations to spread disk IO

Locations

A database can be extended to use extra database and work locations

A table– Can be spread across locations– Spread across too many locations may degrade

performance Need to understand disk set up for

– WAN– SAN– Raid

Locations

Alternative locations can be created through – Accessdb– SQL statements– Extenddb

To use a location a table must be– Relocated– Reorganized

System catalogs are always in the database “home location”

Tables

Single location verses multiple locations Page size Compressed verses non-compressed Indexing Table structure

Partitioned Tables

Queries can scan relevant partitions Can make use of Parallel Query Table partitions can be in different locations A partition can be in multiple locations A table can be partitioned by a “distribution”

– HASH– List– Range– Automatic

Example

Create table employee ( emp_no integer not null not default, emp_name char(32) not null not default, dept_no integer)with partition = ( (list on dept_no partition p1 values (1, 2), partition p2 values (3, 4), partition p3 values (DEFAULT)) subpartition (hash on emp_no 16 partitions) ); modify employee to btree unique on dept_no, emp_no;

Pages

Page size = DMF cache size used Functionality verses performance Lock level

– Table– Page– Row

CPU

User threads Internal Threads Other things

User threads

Number of concurrent connections – SQL sent– Data returned

Internal threads

Dead Process Detector thread Force Abort thread Group Commit thread Consistency Point(CP) thread Event thread WriteBehind(WB) thread (for each configured cache) Replicator Queue Manager thread Terminator thread Parallel Query threads Parallel Sort threads Log writer threads

Parallel Query

Partitioning not required for parallel query Partitioning enables more parallelism Partition compatible joins in parallel threads

Parallel Query

opf_pq_dop– Defines the maximum number of exchange

nodes that can be compiled into a query plan – 0 or 1 prevents the generation of parallel plans– Any other positive value enables them– Default 8– Maximum 32

Parallel Query

opf_pq_partthread– Undocumented and not in config.dat– Defines the maximum number of threads per

exchange node– Default 2– Testing show that more than 6 adds no value

Parallel Query

opf_pq_threshold– Defines the cost threshold that a query plan must

exceed before a parallel plan is generated– The cost estimate is the sum of the C and D

numbers at the top of the query plan– Default 1000

Parallel Query

Set [No]Parallel <nn>– Controls the generation of parallel query plans – Can be used to override opf_pq_dop– nn indicates the degree of parallelism

• The number of exchange nodes in a plan• Default 4• Maximum 32

Parallel Sort

psort_rows– Sets the threshold in rows for doing a parallel

sort– Sorts of fewer than psort_rows rows will not

consider a parallel sort– The default is 10000 rows

Parallel Sort

psort_nthreads– Controls the number of threads used when

parallel sorting– The default is 2 threads– A machine with many CPU's and large sorts may

benefit from more worker threads– Too many threads

• Will not help sorting • May be slower due to contention

Log Writer threads

1 is not enough Start with 4 or 5 Monitor wait-for-logwriter in logstat Minimize wait-for-logwriter Check log disk if more than 20 configured Consider change to log buffer size

Memory

On 32 bit – maximum of 4 gigabytes On 64 bit – lots more available DBMS Workspace DBMS Resource Logging Locking

DBMS Workspace

For example:– opf_memory– psf_memory– qef_qep_mem– rdf_memory– stack_size

Memory– Allocated in chunks up to the workspace limit– Not obvious how much a session is using

DBMS Workspace

For large installations– Default configuration creates large workspaces

Larger does not mean faster Smaller does not mean less resource usage If queries work

– Do not change Workspace Parameters If some queries take ‘too’ long

– Look at the SQL before changing Parameters, tables structures or indexes

DBMS Resource

For example:– dmf parameters– qsf_memory– qef_sort_mem– rdf_max_tbls

For large installations– Default configuration may set parameters too

small Larger may mean faster Smaller may mean flushing

DMF

Defaults are too small Minimum of 1000 pages for single page caches Larger cache may give gains Massive caches may have decreasing benefit

– Increase and test– 2006 is better than previous releases

Tune intelligently - use the tools – IMA– DM420– Monitor Cache Statistics

DMF: Single page buffers

Tune caches for– Users– Transaction throughput– Table usage

Allow enough pages so that FHDR's, FMAP's, btree root and index pages do not get flushed

Consider using a separate cache for session tables– Session tables can be large– Session tables can be numerous– Session tables do get written to disk if the DMF cache is

required

DMF: CBF - dbms.cache.8K.derived

Derived DBMS Cache Parameters for 8k

Name Value Units Protected

dmf_cache_size 42000 data pages yes

dmf_free_limit 1312 data pages no

dmf_group_count 4500 group buffers no

dmf_memory 638976000 bytes no

dmf_modify_limit 31500 data pages no

dmf_wb_end 12600 data pages no

Tuned cache in stages:

default was 15000 – inadaquateupdate 1 was 32000 – betterupdate 2 was 42000 – good

DMF: Single page buffers : DM420 before

=====Thu Aug 2 04:37:16 2007 ==========! Buffer Cache Configuration ( 8K) -------------------------! Buffer count:78000 Bucket count:77999 Group count:4500 Size:

8! Free count: 8099 Limit:498 Modify count:7911 Limit:13300! Free group count: 4875 Modify group count: 125! Fixed count: 0 Group fixed count: 0! WB start limit: 7500 WB end limit: 5500! WB flushes: 324, Agents cloned: 433! Agents active: 0, Agent hwm: 6! WB pages flushed: 0, WB groups flushed: 0! Summary Statistics ( 8K)

---------------------------------------------------------! GWAIT GSYNC FREEWAIT GW PAGES GW I/O! 0 0 0 2130293 892740! FIX CALLS HITS CHECK REFRESH READ TOSS! 746321221 534464098 4831709 3 859937 82289377

DMF: Single page buffers : DM420 after

=====Thu Aug 2 04:37:16 2007 ==========! Buffer Cache Configuration ( 8K) -------------------------! Buffer count:78000 Bucket count:77999 Group count:4500 Size:

8! Free count: 38751 Limit:1312 Modify count:3249 Limit:31500! Free group count: 4286 Modify group count: 214! Fixed count: 0 Group fixed count: 0! WB start limit: 21000 WB end limit: 12600! WB flushes: 120, Agents cloned: 334! Agents active: 0, Agent hwm: 6! WB pages flushed: 0, WB groups flushed: 0! Summary Statistics ( 8K)

---------------------------------------------------------! GWAIT GSYNC FREEWAIT GW PAGES GW I/O! 0 0 0 220821 79740! FIX CALLS HITS CHECK REFRESH READ TOSS! 656525242 643102876 3341709 3 355997 75279473

DMF: Single page buffers : DM420 before

Stats for FHDR pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 1192214 98421 1 0 23354 573440snip! Stats for FMAP pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 1032639 99626 1 0 23222 593242snip! Stats for ROOT pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 173121327 122332111 0 0 12438 9196snip! Stats for INDEX pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 10987543 10542532 0 0 7037 79599snip! Stats for LEAF pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 364864202 309868363 0 0 128483 3443724

DMF: Single page buffers : DM420 after

Stats for FHDR pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 1004114 398096 1 0 14374 603510snip! Stats for FMAP pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 1005639 399626 1 0 14375 603541snip! Stats for ROOT pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 186263140 186247369 0 0 12128 10129snip! Stats for INDEX pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 11613185 11597531 0 0 7037 80979snip! Stats for LEAF pages:! FIX CALLS HITS CHECK REFRESH READ TOSS! 277170152 276704306 0 0 148883 2413774

DMF: Group buffers

Tune buffers for queries Tune queries to keep group buffer usage to a

minimum Switch on Gather Write Setting Group Buffers to zero does not result in

no group buffers

QSF

Query Storage Facility Global memory area Used for storing query objects Used to pass information between facilities Monitor using

– Trace points• QS501 – QS512

– IMA

Logging

Log buffers– Number– Size

“logstat –statistics to tune log parameters – Log Waits:

• Free Buffer• Split Buffer

– Buffer utilization profile– All logwriters busy– Max write queue length– Max write queue count

Logging

Log buffers– Number - default 35 (recom. 200)– Size - default 4K (recom. 8K)

“logstat –statistics to tune log parameters – Log Waits:

• Free Buffer• Split Buffer

– Buffer utilization profile– All logwriters busy– Max write queue length– Max write queue count

Logging

Log buffers– Number - default 35 (recom. 200)– Size - default 4K (recom. 8K)

“logstat –statistics to tune log parameters – Log Waits:

• Free Buffer• Split Buffer

– Buffer utilization profile– All logwriters busy– Max write queue length < Number of buffers– Max write queue count

Logging----Current log file header-----------------------------------------------------

Block size: 8192 Block count: 62500 Partitions: 1 Buffer count: 200 CP interval: 5120 Logfull interval: 56250 Abort interval: 45000 Last Transaction Id: 0000455B4B0FBE8F Begin: <1163633519:37587:2448> CP: <1163633519:42735:5956> End:

<1163633519:43170:1224>

Percentage of log file in use or reserved: 8 Log file blocks reserved by recovery system: 0 Archive Window: <1163633519,42725,5956>..<1163633519,43170,1224> Previous CP: <1163633519,37587,2448> Status: ONLINE,ECPDONE Active Log(s): II_LOG_FILE

Logging ====Fri May 11 01:42:50 2007 Logging System Summary====== Database add 1068 Database removes 1014 Transaction begins 5979858(6M) Transaction ends 5979559 Log read i/o's 126345 Log write i/o's 126835 Log writes 1209002 Log forces 2807 Log waits 10313 Log split waits 0 Log free waits 0 Log stall waits 8 Log BCP waits 8 Logfull stall waits 0 Log group commit 8337 Log group count 8379 Check commit timer 2326 Timer write 2326 Timer write, time 2 Timer write, idle 2324 Inconsistent db 0 Kbytes written 175777 ii_log_file read 126345 ii_dual_log read 0 write complete 126837 dual write complete 0 All logwriters busy 1369 Max write queue len 85 Max write queue cnt 1----Buffer utilization profile--------------------------------------------------------------- <10% ********* 10-19% *************** 20-29% ********************** 30-39% ** 40-49% *** 50-59% ** 60-69% * 70-79% * 80-89% * >90% *********

Logging ====Thu Aug 2 04:37:16 2007 Logging System Summary====== Database add 7558 Database removes 7396 Transaction begins 23557021(23M) Transaction ends 23556713 Log read i/o's 511846 Log write i/o's 515768 Log writes 4435689 Log forces 11185 Log waits 45831 Log split waits 0 Log free waits 0 Log stall waits 32 Log BCP waits 32 Logfull stall waits 0 Log group commit 26852 Log group count 27024 Check commit timer 7782 Timer write 7782 Timer write, time 0 Timer write, idle 7782 Inconsistent db 0 Kbytes written 654183 ii_log_file read 511846 ii_dual_log read 0 write complete 515767 dual write complete 0 All logwriters busy 1001 Max write queue len 99 Max write queue cnt 1----Buffer utilization profile-------------------------------------------------- <10% ************* 10-19% ***************** 20-29% *************** 30-39% ***** 40-49% **** 50-59% ** 60-69% * 70-79% * 80-89% * >90% *******

Locking

Large installations can generate huge– Lock limits– Resource limits– Result in large lock/log shared memory segments

“lockstat –statistics” to tune lock parameters – High-water marks for:

• Lock lists• Locks• Resources• Max locks per transaction

Locking=====Fri May 11 01:42:50 2007 Locking System Summary================= Total Locks 757500 Total Resources 505000 Locks per transaction 3000 Lock hash table 100999 Locks in use 956 Resource hash table 10099 Resources in use 902 Total lock lists 530 Lock lists in use 83=====Fri May 11 01:42:50 2007 Locking System Statistics============== Create lock list 5980545 Release lock list 5980386 Request lock 107257541 Re-request lock 21338874 Convert lock 257715 Release lock 104970761 Escalate 467 Lock wait 80 Convert wait 0 Convert Deadlock 0 Deadlock Wakeups 21 Max dlk queue len 1 Deadlock Search 21 Deadlock 0 Cancel 0 Convert Search 0 Allocate CB 111698597 Deallocate CB 213755494 LBK Highwater 3 LLB Highwater 95 SBK Highwater 3 LKB Highwater 6019 RBK Highwater 9 RSB Highwater 5975 Max Local dlk srch 0 Dlk locks examined 21 Max rsrc chain len 22 Max lock chain len 21 Max locks per txn 3001 Callback Wakeups 0 Callbacks Invoked 0 Callbacks Ignored 0

Locking=====Thu Aug 2 04:37:16 2007 Locking System Summary================= Total Locks 180000 Total Resources 120000 Locks per transaction 10000 Lock hash table 23993 Locks in use 1047 Resource hash table 23993 Resources in use 968 Total lock lists 2160 Lock lists in use 102=====Thu Aug 2 04:37:16 2007 Locking System Statistics============== Create lock list 23566093 Release lock list 3565717 Request lock 260246455 Re-request lock 58993453 Convert lock 3696830 Release lock 252073614 Escalate 652 Lock wait 196 Convert wait 5 Convert Deadlock 0 Deadlock Wakeups 122 Max dlk queue len 4 Deadlock Search 130 Deadlock 1 Cancel 1 Convert Search 0 Allocate CB 280445255 Deallocate CB 525058377 LBK Highwater 3 LLB Highwater 119 SBK Highwater 3 LKB Highwater 12787 RBK Highwater 10 RSB Highwater 12733 Max Local dlk srch 2 Dlk locks examined 150 Max rsrc chain len 48 Max lock chain len 47 Max locks per txn 5175 Callback Wakeups 0 Callbacks Invoked 0 Callbacks Ignored 0

A few words about tuning

– Have a plan– Tune with care– Know the performance baseline– Change one thing at a time– Measure the change– Understand parameter interactions– Monitor important E_*

• E_DMA00D_TOO_MANY_LOG_LOCKS

A few words about tuning

– Have a plan– Tune with care– Know the performance baseline– Change one thing at a time– Measure the change– Understand parameter interactions– Monitor important E_* errors.

• E_DMA00D_TOO_MANY_LOG_LOCKS• E_DM004B_LOCK_QUOTA_EXCEEDED• E_DM9041_LK_ESCALATE_TABLEMaximum number of

locks for transaction exceeded. Escalating to table-level lock on table iiprotect in database mydb

A few more words about tuning

– Tuning is not difficult– Monitoring is a continuous process– Be pro-active– Health checks can save on Hardware costs– Non-stressed installations run for longer

Summary

Tune with care Have a plan Go on a training course Ask an expert

Questions&

Answers

DBMSPerformance Tuning