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https://issues.apache.org/jira/browse/HBASE-2248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12855160#action_12855160
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stack commented on HBASE-2248:
------------------------------
Why do this?
{code}
- List<KeyValue> results = new ArrayList<KeyValue>();
- store.get(get, null, results);
- return new Result(results);
+ get.addFamily(family);
+ return get(get, null);
{code}
Is it because of this....up in HRegion:
{code}
+ // The reason why we set it up high is so that each HRegionScanner only
+ // has a single read point for all its sub-StoreScanners.
+ ReadWriteConsistencyControl.resetThreadReadPoint(rwcc);
{code}
This bit of the patch looks like its breaking the accumulation of qualifiers:
{code}
- List<KeyValue> result = new ArrayList<KeyValue>(1);
- Get g = new Get(kv.getRow());
- g.setMaxVersions(count);
- NavigableSet<byte []> qualifiers =
- new TreeSet<byte []>(Bytes.BYTES_COMPARATOR);
- qualifiers.add(qual);
- get(store, g, qualifiers, result);
+ Get get = new Get(kv.getRow());
+ get.setMaxVersions(count);
+ get.addColumn(family, qual);
+
+ List<KeyValue> result = get(get);
+
{code}
Or is this no longer needed because we go back into Region.get rather than do a
Store.get?
I don't like this if clause style:
+ if (w != null)
+ rwcc.completeMemstoreInsert(w);
I'd suggest you either wrap it in params or put it all on the one line.
For example, undo changes like this I'd say:
{code}
- if(lockid == null) releaseRowLock(lid);
+ if(lockid == null)
+ releaseRowLock(lid);
{code}
I think this needs a comment:
+ private int isScan;
or maybe where its assigned so its clear why it can't be a boolean though its
named as though it were one... maybe change its name?
I don't get this:
{code}
+ // TODO call the proper GET API
// Get the old value:
Get get = new Get(row);
{code}
or this:
{code}
+ //noinspection SuspiciousMethodCalls
{code}
Why this change Ryan?
{code}
-class KeyValueSkipListSet implements NavigableSet<KeyValue>, Cloneable {
+class KeyValueSkipListSet implements NavigableSet<KeyValue> {
{code}
Its crazy how much code you've removed from MemStore around #195.
Ok, thats enough for now
> Provide new non-copy mechanism to assure atomic reads in get and scan
> ---------------------------------------------------------------------
>
> Key: HBASE-2248
> URL: https://issues.apache.org/jira/browse/HBASE-2248
> Project: Hadoop HBase
> Issue Type: Bug
> Affects Versions: 0.20.3
> Reporter: Dave Latham
> Priority: Blocker
> Fix For: 0.20.4
>
> Attachments: HBASE-2248-demonstrate-previous-impl-bugs.patch,
> HBASE-2248-GetsAsScans3.patch, HBASE-2248-rr-alpha1.txt,
> HBASE-2248-rr-alpha2.txt, HBASE-2248-rr-alpha3.txt, HBASE-2248-ryan.patch,
> hbase-2248.gc, HBASE-2248.patch, hbase-2248.txt, readownwrites-lost.2.patch,
> readownwrites-lost.patch, Screen shot 2010-02-23 at 10.33.38 AM.png,
> threads.txt
>
>
> HBASE-2037 introduced a new MemStoreScanner which triggers a
> ConcurrentSkipListMap.buildFromSorted clone of the memstore and snapshot when
> starting a scan.
> After upgrading to 0.20.3, we noticed a big slowdown in our use of short
> scans. Some of our data repesent a time series. The data is stored in time
> series order, MR jobs often insert/update new data at the end of the series,
> and queries usually have to pick up some or all of the series. These are
> often scans of 0-100 rows at a time. To load one page, we'll observe about
> 20 such scans being triggered concurrently, and they take 2 seconds to
> complete. Doing a thread dump of a region server shows many threads in
> ConcurrentSkipListMap.biuldFromSorted which traverses the entire map of key
> values to copy it.
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