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https://issues.apache.org/jira/browse/DERBY-1068?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12557065#action_12557065
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quartz commented on DERBY-1068:
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> Derby does reuse space in the table when subsequent inserts come in.
> The level of reuse tends to be when a whole page of data becomes deleted.
This is not true. From the doc of SYSCS_UTIL.SYSCS_COMPRESS_TABLE, as is:
"Typically, unused allocated space exists when a large amount of data is
deleted from a table, or indexes are updated. By default, Derby does not return
unused space to the operating system."
Normal tests tables show the seg0/ folder takes about 40 MB.
The crashed customer where the compress isn't working had a seg0/ folder of
about 480 MB!
I must call a compress periodically.
In place or not, it has to be completely safe, concurrent or not. What I meant
is that issuing an insert while compressing shouldn't result in either of the
statement failing.
> change of store contract: online compress operations should not share any
> locks with user transactions
> ------------------------------------------------------------------------------------------------------
>
> Key: DERBY-1068
> URL: https://issues.apache.org/jira/browse/DERBY-1068
> Project: Derby
> Issue Type: Improvement
> Components: Store
> Reporter: Andreas Korneliussen
> Assignee: Mike Matrigali
> Priority: Minor
>
> Propose to add the following to the store contract:
> * truncate and compress requires exclusive table locking
> * the truncate, purge and compress operations do not share any locks with
> user transactions
> Currently the store implementation allows users to share locks in truncate
> and possibly purge.
> This request is driven by:
> http://www.nabble.com/conflict-detection-strategies-t1120376.html#a2938142
> and:
> http://www.nabble.com/RowLocation-contract-from-storage-engine-t1142235.html#a2994156
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