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https://issues.apache.org/jira/browse/HBASE-5416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13585211#comment-13585211
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Lars Hofhansl commented on HBASE-5416:
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Moving the method to FilterBase is a great idea and a good compromise.
Personally I think implementing Filters directly is rare and I would have a
preference for keeping this in the interface since it is cleaner.
isFamilyEssential is very useful for future scan performance enhancements, I
would hate to see it vanish again from the Filter interface. (Incidentally in
trunk Filter is now a class, which would have allowed us to make changes
without this problem).
As alternative can we add to the Javadoc of Filter a note to avoid implementing
it directly and rather extend FilterBase?
[~davelatham] If this is a hassle for you I think we're all in agreement that
we should push the method down to FilterBase.
[~stack] I think you'd prefer the push into FilterBase. Let's just do that.
> 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: Sergey Shelukhin
> Fix For: 0.96.0, 0.94.5
>
> Attachments: 5416-0.94-v1.txt, 5416-0.94-v2.txt, 5416-0.94-v3.txt,
> 5416-drop-new-method-from-filter.txt, 5416-Filtered_scans_v6.patch,
> 5416-v13.patch, 5416-v14.patch, 5416-v15.patch, 5416-v16.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, HBASE-5416-v10.patch,
> HBASE-5416-v11.patch, HBASE-5416-v12.patch, HBASE-5416-v12.patch,
> HBASE-5416-v7-rebased.patch, HBASE-5416-v8.patch, HBASE-5416-v9.patch,
> org.apache.hadoop.hbase.regionserver.TestHRegion-output.txt
>
>
> 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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