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From "stack (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5416) Improve performance of scans with some kind of filters.
Date Thu, 16 Feb 2012 21:32:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13209760#comment-13209760

stack commented on HBASE-5416:

Interesting idea.  Patch looks pretty non-invasive to add some nice functionality.  Would
appreciate some better doc in the filters package doc or over in the manual to accompany this
change.  Nice one Max.

Comments on patch:

Please follow the convention you see in the surrounding file and parenthesize code blocks.
 E.g. in the below:

+  @Override
+  public boolean isFamilyEssential(byte[] name) {
+    for (Filter filter : filters)
+      if (filter.isFamilyEssential(name))
+        return true;
+    return false;
+  }

What is a 'joinedScanner' in the below:

+      List<KeyValueScanner> joinedScanners = new ArrayList<KeyValueScanner>();


It needs a bit of a comment I'd say.

Why drop the check for empty results in below?

-          if (results.isEmpty() || filterRow()) {
+          boolean filtered = filterRow();

Please submit a patch with a --no-prefix so we can see how your patch does against hadoopqa.
> 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
>         Attachments: Filtered-scans_0.90.4.patch, Filtered-scans_trunk.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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