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https://issues.apache.org/jira/browse/DERBY-269?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mike Matrigali updated DERBY-269:
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I have not seen any other suggestions, how about the following zero admin
solution? It is not perfect - suggestions welcome.
Along with the statistics storing, save how many rows were in the table when
exact statistics were calculated. This number is
0 if none have been calculated because index creation happened on an empty
table. At query compile time when we look
up statistics we automatically recalculate the statistics at certain
threshholds - say something like row count growing past next threshhold : 10,
100, 1000,
100000 - with upper limit being somewhere around how many rows we can process
in some small amount of time - like 1 second on a modern laptop. If we are
worried about response time, maybe we background queue the stat gathering
rather than waiting with maybe
some quick load if no stat has ever been gathered. The background gathering
could be optimized to not interfere with locks by
using read uncommitted.
I think it would be useful to also have the manual call just to make it easy to
support customers and debug issues in the field. There is proably always some
dynamic data distribution change that in some case won't be picked up by the
automatic algorithm.
Also just very useful for those who have complete control of the create ddl,
load data, run stats, deliver application process.
> Provide some way to update index cardinality statistics (e.g. reimplement
> update statistics)
> --------------------------------------------------------------------------------------------
>
> Key: DERBY-269
> URL: https://issues.apache.org/jira/browse/DERBY-269
> Project: Derby
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 10.0.2.0, 10.0.2.1, 10.1.1.0, 10.2.2.0, 10.3.1.4
> Reporter: Stan Bradbury
>
> Performance problems are being reported that can be resolved by updating the
> cardinality statistics used by the optimizer. Currently the only time the
> statistics are guaranteed to be an up-to-date is when the index is first
> created on a fully populated table. This is most easily accomplished on an
> existing table by using the command:
> alter table <table-name> compress [sequential]
> Compress table is an I/O intensive task. A better way to achieve this would
> be to re-enable parser support for the 'update statistics' command or
> re-implement the update in some other fashion.
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