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From "Ted Yu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5416) Improve performance of scans with some kind of filters.
Date Sat, 22 Dec 2012 00:11:13 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13538563#comment-13538563

Ted Yu commented on HBASE-5416:

I think the rewritten logic is easier to understand.
+  public static final String LOAD_CFS_ON_DEMAND_CONFIG_KEY = "hbase.hregion.scan.loadColumnFamiliesOnDemand";
Wrap long line.
+   public boolean isLoadingCfsOnDemandDefault() {
Can the 'Default' be dropped from the method name ? We're interested in whether on demand
loading is on.
+      List<KeyValueScanner> joinedScanners = new ArrayList<KeyValueScanner>();
Should we check scan.doLoadColumnFamiliesOnDemand() first so that we don't allocate ArrayList
if this feature is turned off ?
+     * Fetches records with this row into result list, until next row or limit (if not -1).
'this row' -> 'currentRow'
'result list' -> 'results list'
+        // Check if we were getting data from the joinedHeap abd hit the limit.
'abd' -> 'and'
+          // Techically, if we hit limits before on this row, we don't need this call.
Typo: Techically
+          // Populating from the joined map was stopped by limits, populate some more.
'joined map' -> 'joined heap'
+        // the case when SingleValueExcludeFilter is used.
SingleValueExcludeFilter -> SingleColumnValueExcludeFilter
> 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
>         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, 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,
> 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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