[HBASE-1206] Scanner spins when there are concurrent inserts to column family

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.19.0
• Fix Version/s: 0.20.0
• Assignee: Unassigned
• Reporter: Ben Maurer
• Created: 20/Feb/09 04:36
• Updated: 13/Sep/09 22:24
• Resolved: 16/Jun/09 16:12

Description

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) {
01:13 < BenM> if (columnMatch)

{ 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: }

Issue Links

• is part of: HBASE-1304 New client server implementation of how gets and puts are handled.
• is related to: HBASE-1249 Rearchitecting of server, client, API, key format, etc for 0.20
• relates to: HBASE-867 If millions of columns in a column family, hbase scanner won't come up