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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1206) Scanner spins when there are concurrent inserts to column family
Date Tue, 10 Mar 2009 21:06:50 GMT

    [ 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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