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https://issues.apache.org/jira/browse/DERBY-2487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12679611#action_12679611
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Rick Hillegas commented on DERBY-2487:
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Thanks for working on this issue, Bryan. Like Knut and yourself, I am a little
concerned that we are creating many system catalogs for one feature. I like the
idea that the plan-capturing tables should be created on-demand in a user
schema. You could imagine adding a new overload of
syscs_util.syscs_set_runtimestatistics:
call syscs_util.syscs_set_runtimestatistics( 'myStatisticsSchema' )
This would
1) Create myStatisticsSchema (owned by the current user) if it didn't already
exist.
2) Create the plan-bearing tables in myStatisticsSchema if they didn't already
exist or if their shape is stale. I think that the contract should be that the
layout of these tables can change between feature releases. That is, plans are
not guaranteed to survive across upgrade. Derby reserves the right to drop and
recreate these tables after upgrade. Regardless of where we put the statistics,
I think that plans from previous releases should be flushed after upgrade--from
painful previous experience at Sybase I can report that you don't want to be
responsible for persisting plans across upgrade boundaries.
3) Stuff a reference to myStatisticsSchema into the LCC as you suggest. The
contract is that plans are dumped into the latest schema specified by a
syscs_set_runtimestatistics command issued in your session.
Garbage-collecting uninteresting statistics would then just be a matter of
dropping a schema.
> Enhance Derby with EXPLAIN Functionality
> ----------------------------------------
>
> Key: DERBY-2487
> URL: https://issues.apache.org/jira/browse/DERBY-2487
> Project: Derby
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 10.2.2.0
> Reporter: Felix Beyer
> Assignee: Bryan Pendleton
> Priority: Minor
> Attachments: Derby physical XPLAIN schema.png,
> incorporateTrunkChanges.diff, removeSourceDepth.diff, RSProtocolNew.pdf,
> rts.xls, small logical xplain schema.pdf, startRegressionTest.diff,
> startRegressionTest.diff, startUpgradeTests.diff, updateRegressionTests.diff,
> updateRegressionTests.diff, usage.txt, xplain_patch_v1.txt, xplainClasses.pdf
>
>
> This enhancement extends Derby with EXPLAIN functions. Users want to have
> more feedback than they`re getting with the current RuntimeStatistics
> facility. This extension is based on the
> RuntimeStatistics/ResultSetStatistics functions / classes.
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