Ugif 10 2012 ppt0000001
Transcript of Ugif 10 2012 ppt0000001
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User Group Informix France
Partition Defragmenter
Yoram [email protected]
Mercredi 3 Octobre 2012Mercredi 3 Octobre 2012
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AgendaAgenda
�A bit of partition background�The problem with fragmented data�How does the feature work�Functionality & considerations�Defragmenter in OAT�Example
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A bit of partition background�What is an extent ?
– Collection of physically contiguous pages on disk
– Extent can hold data page, index page, bitmap page etc…
�What is a partition ?– Logical collection of all the extents allocated for a
given table or index.
– Space for partition is allocated in units of extents and is not necessarily contiguous.
�Each partition are unique within the system– oncheck –pt <partnum>
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A bit of partition background
Partition logical to physical extent relationship
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A bit of partition background
Extents for table A
Extents for
other tables
Chunk 14
Free pages
�Before Defragmenting
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�After Defragmenting
Chunk 14
Extents for table A
A bit of partition background
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A bit of partition background
7
�Previous Solutions– Table unload and reload
�Oncheck –me– Off-line table reorganization– Non-recoverable
– Unsupported
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A bit of partition background
�How many extents exist ?– Run oncheck –pe.– Run oncheck –pt.
– SQLdatabase sysmaster; select unique te_partnum, count(*) from systabextents group by 1 having count(*) > NN order by 1 desc;
• Where NN is a value.
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The problem with fragmented data
�What’s the problem with many extents? – Full partition page.
• Prohibits new inserts.– Might not be at maximum number of rows.
• Need to either delete older entries, if possible.– or
• Requires a manual table recreation.
– (FYI: Actually, this can no longer exist in 11.70)
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�Many extents degrades performance.– Need to skip over non-contiguous disk areas.– Slower retrieval of data.
– Mapping logical page numbers to physical addresses is slower.
– Chunk allocations are slower with long free list pages
– Archive extent-sorting phase is slower
The problem with fragmented data
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�What’s the problem with many extents? – Many tables with many extents feels
overbearing.• Outputs from oncheck –pe & -pt.
The problem with fragmented data
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How does the feature work
�Run new SQL API functions.– sysadmin database.
– execute function [admin|task] ("<defragment","<database>:[<owner>.]<table>[#index]")
• or
– execute function [admin|task] ("<defragment partnum", "<partnum> [, <partnum>, ... ]”);
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How does the feature work
– What goes on behind the scenes.• Check validity.
• Create new extent.• Might need just one adding
• Start a loop and process all old extents.– Read old extent.– Move all old extent pages to the new extent.– Delete old extent.
• Loop end.
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How does the feature work
�Log the work using five new log types.– Start defragmentation.
– End defragmentation.– Add new defragmentation extent.
– Remove old defragmentation extent.– Move page.
�Will result in a surge in logical log usage.
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How does the feature work
�Monitoring progress.– onstat -g defragment.
• Searching for extents.• Merging extents.• Defrag_completed.• Defrag_failed.
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How does the feature work
�Recoverable if server shuts down or crash
– Defragmenter cleaner thread will remove extra extents after fast recovery
• Rolls back current unit of work (UOW) if needed.– 08:52:06 Defragmenter cleaner thread now running– 08:52:06 Defragmenter cleaner thread cleaned:1 partitions
– Will the object be consistent ?• Yes.
– Choose to run again to complete the job.
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�Can defragment table online�No locks placed on object�Only allowed one defragmenter running per
dbspace�Replication is supported (HDR, MACH11, ER)�Run via the SQL API interface.
Functionality
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�Functionality not allowed – Functional indexes.
– VTI & VII objects.– Temporary tables.
– Sort tables.– Optical blobs.
– System catalog tables
Considerations
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�Cannot stop once job submitted�Cannot run simultaneously when table being
– Altered– Truncated
– Drop– Compress, Repack, Shrink
�Not the same as compress/repack/shrink
Considerations
�Enterprise Replication.– Table needs to be in CDR alter mode.
• Mode unset automatically at end of job
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�Operation is logging-intensive– Each page move is logically logged (DFMVPG)
• 70-80 bytes per page moved
�Small units of work to avoid long transaction.– It may send other transactions over the threshold
�New extents created at end of dbspace.�Schedule during low activity.�Perform after a backup.
Considerations
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Defragmenter in OAT
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On the OAT menu, expand
Space Administration > Space Optimization
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Defragmenter in OAT
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Select the tables.
On the Actions menu, click Optimize Space.
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Defragmenter in OAT
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Select Defragment extents and click OK.
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�Automatic Storage Optimization– Can automate defragmenting using OAT.
– Enabled via scheduler task “auto_crsd”• This can also do compressing, repacking, shrinking.• ‘crsd’ stand for compress, repack, shrink, defragment
– This can also be enabled via SQL
Defragmenter in OAT
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�‘auto_crsd’ task details– In OAT -> Task Scheduler -> Task Details
• UPDATE ph_task SET tk_enable = 'T‘ WHERE tk_name = 'auto_crsd';
Defragmenter in OAT
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�‘auto_crsd’ task parameters.
– UPDATE ph_threshold SET value = 'F WHERE name = 'AUTODEFRAG_ENABLED';
– UPDATE ph_threshold SET value = ‘100‘ WHERE name = 'AUTODEFRAG_EXTENTS';
Defragmenter in OAT
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Example
� SQL to create three fragmented tables– create table tab1 (a serial, b int, c int);– create table tab2 (a serial, b int, c int);– create table tab3 (a serial, b int, c int);– create procedure ins (a int, b int) define c int;
• for c = a to b• insert into tab1 values (0, 88, 99);• insert into tab2 values (0, 88, 99);• insert into tab3 values (0, 88, 99);• end for;
– end procedure;– execute procedure ins (1, 1000000);
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Example
�oncheck –pe before defragment.
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Example
� oncheck –pt before defragment.– FYI : in 11.70 No longer limited to one partn page.
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Example
�SQL API function.– execute function task ("defragment", "oltr:tab1");
(expression) OK
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Example
�oncheck –pe after defragment.
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Example
�oncheck –pt after defragment.
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Example
�onlog output
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SummarySummary
�Informix Defragmenter Capabilities
– Partition Extents Defragmentation– New System Admin SQL API
– OAT GUI Interface– Automatic Defragmentation
– Can be completed with compress/repack/shrink for optimal storage optimization
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Questions ?
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MerciMerci
Yoram [email protected]
Mercredi 3 Octobre 2012Mercredi 3 Octobre 2012