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Posted to dev@hbase.apache.org by "stack (JIRA)" <ji...@apache.org> on 2009/03/10 22:06:50 UTC
[jira] Commented: (HBASE-1206) Scanner spins when there are
concurrent inserts to column family
[ https://issues.apache.org/jira/browse/HBASE-1206?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12680616#action_12680616 ]
stack commented on HBASE-1206:
------------------------------
Can I push this refactor out to 0.19.2 Ben? ColumnMatch should run faster after hbase-1253 if that'll help any.
> Scanner spins when there are concurrent inserts to column family
> ----------------------------------------------------------------
>
> Key: HBASE-1206
> URL: https://issues.apache.org/jira/browse/HBASE-1206
> Project: Hadoop HBase
> Issue Type: Bug
> Affects Versions: 0.19.0
> Reporter: Ben Maurer
> Fix For: 0.19.1
>
>
> I had a MR job that would launch multiple scanners on a region that made updates to the same column family as they were scanning on (but not the same column). As a result, there were lots of processes that had to grep through all of the irrelevent inserts many times as flushes occurred.
> However, if I put the column that I was outputting to in the list of columns to scan for, everything worked quickly.
> The code that's causing this is:
> 01:13 < BenM> keys[i] = new HStoreKey(HConstants.EMPTY_BYTE_ARRAY, this.store.getHRegionInfo());
> 01:13 < BenM> if (firstRow != null && firstRow.length != 0) {
> 01:13 < BenM> if (findFirstRow(i, firstRow)) {
> 01:13 < BenM> continue;
> 01:13 < BenM> }
> 01:13 < BenM> }
> 01:13 < BenM> while (getNext(i)) {
> 01:13 < BenM> if (columnMatch(i)) {
> 01:13 < BenM> break;
> 01:13 < BenM> }
> 01:13 < BenM> }
> columnMatch() on the stuff that just got flushed out never returns true. This caused lots of problems to build up.
> The fix for this is:
> (10:58:30 PM) BenM: IMHO, this is a somewhat easier issue to fix
> (10:58:38 PM) BenM: i think it could be done in a way that cleans up the code
> (10:58:50 PM) BenM: right now, the code just scans through each of the map files
> (10:59:02 PM) BenM: without regard to the relative key positions
> (10:59:12 PM) BenM: i think it could use a priority queue so that it only works on the relevent files
> (11:01:22 PM) St^Ack_: BenM: please expand, I don't follow exactly
> (11:01:50 PM) BenM: lets say we have two map files
> (11:02:09 PM) BenM: one with 1/foo:bar 2/foo:bar 3/foo:bar
> (11:02:17 PM) BenM: (row/family:col)
> (11:02:31 PM) BenM: and the other with 1000/blah:blah 1001/blah:blah
> (11:02:39 PM) BenM: the curent logic is
> (11:02:44 PM) BenM: for each map file:
> (11:02:56 PM) BenM: find the first potential row in this file
> (11:03:08 PM) BenM: look at min(all potential rows)
> (11:03:34 PM) BenM: the algorith should be:
> (11:03:43 PM) BenM: q = new PriorityQueue()
> (11:04:05 PM) BenM: for each map file: insert the HStoreKey of the first key in the file
> (11:04:17 PM) BenM: while(k = q.pop()) {
> (11:04:37 PM) BenM: if (k is intersting) break;
> (11:04:37 PM) BenM: advance k
> (11:04:37 PM) BenM: q.push(k)
> (11:04:38 PM) BenM: }
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