[
https://issues.apache.org/jira/browse/DERBY-3937?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12645303#action_12645303
]
Martin Hajduch commented on DERBY-3937:
---------------------------------------
Ok. I understand your explanation. At the same time, I can imagine that there
are applications which need functions like COUNT/MIN/MAX to be performed faster
then by scanning through all rows. Also, some applications would need to
implement support for 'paging' - for which I haven't found any viable solution
yet using Derby.
Are there any plans of development in these directions ? Does Derby has
something 'else' to make it possible to develop 'paging' over huge amount of
rows ? Or is this not priority at the moment ?
Are there some speedups possible ? For example count of index entries per page
? Or would that not bring any significant benefit over current scan ?
Any idea how Oracle manages this ?
> Select count(*) scans all the rows (and is therefore slow with big tables),
> is the amount of rows not available/known for example in index ?
> --------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-3937
> URL: https://issues.apache.org/jira/browse/DERBY-3937
> Project: Derby
> Issue Type: Improvement
> Components: Performance
> Environment: Any
> Reporter: Martin Hajduch
>
> Create table with 5000000 rows. Create index on unique ID. Select count(*) on
> such table is going to take quite some time.
> Shouldn't the index contain amount of indexed rows and the value taken from
> there ?
> Additionally, queries of the form select count(*) from table where
> col1=value; take lots of time (depending on amount of rows satisfying WHERE
> clause) even if index on col1 exists. Isn't it possible to find first and
> last occurence in the index, and then calculate amount of rows more
> effectively then scanning through all of them ?
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
