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From "Sergey Shelukhin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5416) Improve performance of scans with some kind of filters.
Date Thu, 13 Dec 2012 22:34:14 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13531586#comment-13531586

Sergey Shelukhin commented on HBASE-5416:

With default setting, I got tired of waiting for it after an ~hour and canceled it. I think
it was still inserting rows, although my laptop drive was extreley sluggish so maybe logs
haven't flushed so I didn't see "Data inserted" log message.
However, after changing the number of writes to 5k, I get very impressive performance improvement:
2012-12-13 14:25:48,699 INFO  [main] regionserver.TestJoinedScanners(155): Slow scanner finished
in 5.15852 seconds, got 50 rows
2012-12-13 14:25:48,931 INFO  [main] regionserver.TestJoinedScanners(175): Joined scanner
finished in 0.231946 seconds, got 50 rows

It looks like it would be a good idea from perf standpoint to include this in trunk.
[~shmuma] do you want to continue on the patch? Otherwise I can continue on it.
I think we'd want to make it optional (in config and/or per request) to address some of the
stability concerns.
I want to look at patch in more detail too to see what more testing can be done. It seems
like maybe two LoadTestTool-s writing and verifying against the same table in parallel could
be used, or something, in an integration test.

I get "Filter with filterRow(List<KeyValue>) incompatible with scan with limit!" in
testScanner_JoinedScannersAndLimits after rebase, I'll look into it.
> Improve performance of scans with some kind of filters.
> -------------------------------------------------------
>                 Key: HBASE-5416
>                 URL: https://issues.apache.org/jira/browse/HBASE-5416
>             Project: HBase
>          Issue Type: Improvement
>          Components: Filters, Performance, regionserver
>    Affects Versions: 0.90.4
>            Reporter: Max Lapan
>            Assignee: Max Lapan
>             Fix For: 0.96.0
>         Attachments: 5416-Filtered_scans_v6.patch, 5416-v5.txt, 5416-v6.txt, Filtered_scans.patch,
Filtered_scans_v2.patch, Filtered_scans_v3.patch, Filtered_scans_v4.patch, Filtered_scans_v5.1.patch,
Filtered_scans_v5.patch, Filtered_scans_v7.patch
> When the scan is performed, whole row is loaded into result list, after that filter (if
exists) is applied to detect that row is needed.
> But when scan is performed on several CFs and filter checks only data from the subset
of these CFs, data from CFs, not checked by a filter is not needed on a filter stage. Only
when we decided to include current row. And in such case we can significantly reduce amount
of IO performed by a scan, by loading only values, actually checked by a filter.
> For example, we have two CFs: flags and snap. Flags is quite small (bunch of megabytes)
and is used to filter large entries from snap. Snap is very large (10s of GB) and it is quite
costly to scan it. If we needed only rows with some flag specified, we use SingleColumnValueFilter
to limit result to only small subset of region. But current implementation is loading both
CFs to perform scan, when only small subset is needed.
> Attached patch adds one routine to Filter interface to allow filter to specify which
CF is needed to it's operation. In HRegion, we separate all scanners into two groups: needed
for filter and the rest (joined). When new row is considered, only needed data is loaded,
filter applied, and only if filter accepts the row, rest of data is loaded. At our data, this
speeds up such kind of scans 30-50 times. Also, this gives us the way to better normalize
the data into separate columns by optimizing the scans performed.

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