[
https://issues.apache.org/jira/browse/HBASE-5416?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13539286#comment-13539286
]
ramkrishna.s.vasudevan commented on HBASE-5416:
-----------------------------------------------
I could find one thing here
{code}
// Let's see what we have in the storeHeap.
KeyValue current = this.storeHeap.peek();
boolean stopRow = isStopRow(current);
{code}
Assume i have one CF and i have a filter with isFamilyEssential = true. Also
scan says lazy loading of CF is allowed.
Now in this case i will have only the joinedScanner heap.
So now when the next() is called
current will be null as nothing is there in storeHeap.
Inside isStopRow
{code}
return kv == null || kv.getBuffer() == null ||
(stopRow != null &&
comparator.compareRows(stopRow, 0, stopRow.length,
kv.getBuffer(), kv.getRowOffset(), kv.getRowLength()) <= isScan);
{code}
This will give me true. So stopRow is true.
{code}
if (stopRow) {
if (filter != null && filter.hasFilterRow()) {
filter.filterRow(results);
}
return false;
}
{code}
So this code will just return without scanning. Pls correct me if am wrong?
> 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, HBASE-5416-v9.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.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
