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https://issues.apache.org/jira/browse/HBASE-14221?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ramkrishna.s.vasudevan updated HBASE-14221:
-------------------------------------------
Attachment: HBASE-14221_1.patch
Updated patch correcting the failing test case and the checkstyle comments fix.
In case of BATCH_LIMIT reached in StoreScanner we do a comparison for the row
if it has moved already. this comparison will any way as part of HRegion or in
the StoreScanner while doing next(). There is no logical mistake if we don't
do it here but we do one more while loop in the HRegion layer and that is
altering the scan metrics. Rest are all fine.
Coming to the impact on the perf with scanRange30000 (patched PE tool to scan
bigger ranges) and with filterAll I can see clear difference with and
withoutpatch on latest trunk
With patch
{code}
Min: 379757ms Max: 383591ms Avg: 382071ms
Min: 383131ms Max: 387450ms Avg: 385802ms
{code}
Without patch
{code}
Min: 424281ms Max: 428828ms Avg: 426949ms
Min: 419371ms Max: 422791ms Avg: 421344ms
{code}
> Reduce the number of time row comparison is done in a Scan
> ----------------------------------------------------------
>
> Key: HBASE-14221
> URL: https://issues.apache.org/jira/browse/HBASE-14221
> Project: HBase
> Issue Type: Sub-task
> Components: Scanners
> Reporter: ramkrishna.s.vasudevan
> Assignee: ramkrishna.s.vasudevan
> Fix For: 2.0.0
>
> Attachments: HBASE-14221.patch, HBASE-14221_1.patch,
> withmatchingRowspatch.png, withoutmatchingRowspatch.png
>
>
> When we tried to do some profiling with the PE tool found this.
> Currently we do row comparisons in 3 places in a simple Scan case.
> 1) ScanQueryMatcher
> {code}
> int ret = this.rowComparator.compareRows(curCell, cell);
> if (!this.isReversed) {
> if (ret <= -1) {
> return MatchCode.DONE;
> } else if (ret >= 1) {
> // could optimize this, if necessary?
> // Could also be called SEEK_TO_CURRENT_ROW, but this
> // should be rare/never happens.
> return MatchCode.SEEK_NEXT_ROW;
> }
> } else {
> if (ret <= -1) {
> return MatchCode.SEEK_NEXT_ROW;
> } else if (ret >= 1) {
> return MatchCode.DONE;
> }
> }
> {code}
> 2) In StoreScanner next() while starting to scan the row
> {code}
> if (!scannerContext.hasAnyLimit(LimitScope.BETWEEN_CELLS) ||
> matcher.curCell == null ||
> isNewRow || !CellUtil.matchingRow(peeked, matcher.curCell)) {
> this.countPerRow = 0;
> matcher.setToNewRow(peeked);
> }
> {code}
> Particularly to see if we are in a new row.
> 3) In HRegion
> {code}
> scannerContext.setKeepProgress(true);
> heap.next(results, scannerContext);
> scannerContext.setKeepProgress(tmpKeepProgress);
> nextKv = heap.peek();
> moreCellsInRow = moreCellsInRow(nextKv, currentRowCell);
> {code}
> Here again there are cases where we need to careful for a MultiCF case. Was
> trying to solve this for the MultiCF case but is having lot of cases to
> solve. But atleast for a single CF case I think these comparison can be
> reduced.
> So for a single CF case in the SQM we are able to find if we have crossed a
> row using the code pasted above in SQM. That comparison is definitely needed.
> Now in case of a single CF the HRegion is going to have only one element in
> the heap and so the 3rd comparison can surely be avoided if the
> StoreScanner.next() was over due to MatchCode.DONE caused by SQM.
> Coming to the 2nd compareRows that we do in StoreScanner. next() - even that
> can be avoided if we know that the previous next() call was over due to a new
> row. Doing all this I found that the compareRows in the profiler which was
> 19% got reduced to 13%. Initially we can solve for single CF case which can
> be extended to MultiCF cases.
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