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https://issues.apache.org/jira/browse/HBASE-4465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13121283#comment-13121283
]
[email protected] commented on HBASE-4465:
------------------------------------------------------
bq. On 2011-10-04 23:56:22, Ted Yu wrote:
bq. > src/main/java/org/apache/hadoop/hbase/regionserver/KeyValueHeap.java,
line 306
bq. > <https://reviews.apache.org/r/2180/diff/1/?file=47924#file47924line306>
bq. >
bq. > Should be "lazily-sought"
Somehow "sought" does not sound right for me -- "seek" is a very specific
computer science term here. Replaced with "has done a seek operation" here and
below.
bq. On 2011-10-04 23:56:22, Ted Yu wrote:
bq. >
src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileScanner.java, line
246
bq. > <https://reviews.apache.org/r/2180/diff/1/?file=47930#file47930line246>
bq. >
bq. > Should realSeekDone be set before returning ?
realSeekDone is set to true by enforceSeek() in case we decide we need to do it
as part of requestSeek()
realSeekDone = false; // <-- setting this by default in case lazy seek
// takes effect or enforceSeek() fails
. . .
if (seekTimestamp > maxTimestampInFile) {
// Create a fake key that is not greater than the real next key.
// (Lower timestamps correspond to higher KVs.)
// To understand this better, consider that we are asked to seek to
// a higher timestamp than the max timestamp in this file. We know that
// the next point when we have to consider this file again is when we
// pass the max timestamp of this file (with the same row/column).
cur = kv.createFirstOnRowColTS(maxTimestampInFile);
} else {
// This will be the case e.g. when we need to seek to the next
// row/column, and we don't know exactly what they are, so we set the
// seek key's timestamp to OLDEST_TIMESTAMP to skip the rest of this
// row/column.
enforceSeek(); // <-- this sets realSeekDone
}
bq. On 2011-10-04 23:56:22, Ted Yu wrote:
bq. > src/main/java/org/apache/hadoop/hbase/regionserver/KeyValueHeap.java,
line 371
bq. > <https://reviews.apache.org/r/2180/diff/1/?file=47924#file47924line371>
bq. >
bq. > Should be 'real-sought' and 'lazily-sought'
Done.
bq. On 2011-10-04 23:56:22, Ted Yu wrote:
bq. > src/main/java/org/apache/hadoop/hbase/regionserver/KeyValueScanner.java,
line 101
bq. > <https://reviews.apache.org/r/2180/diff/1/?file=47925#file47925line101>
bq. >
bq. > Should be 'is sought'
Done.
- Mikhail
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On 2011-10-04 22:10:40, Mikhail Bautin wrote:
bq.
bq. -----------------------------------------------------------
bq. This is an automatically generated e-mail. To reply, visit:
bq. https://reviews.apache.org/r/2180/
bq. -----------------------------------------------------------
bq.
bq. (Updated 2011-10-04 22:10:40)
bq.
bq.
bq. Review request for hbase.
bq.
bq.
bq. Summary
bq. -------
bq.
bq. Previously, if we had several StoreFiles for a column family in a region,
we would seek in each of them and only then merge the results, even though the
row/column we are looking for might only be in the most recent (and the
smallest) file. Now we prioritize our reads from those files so that we check
the most recent file first. This is done by doing a "lazy seek" which pretends
that the next value in the StoreFile is (seekRow, seekColumn,
lastTimestampInStoreFile), which is earlier in the KV order than anything that
might actually occur in the file. So if we don't find the result in earlier
files, that fake KV will bubble up to the top of the KV heap and a real seek
will be done. This is expected to significantly reduce the amount of disk IO
(as of 09/22/2011 we are doing dark launch testing and measurement).
bq.
bq. This is joint work with Liyin Tang – huge thanks to him for many helpful
discussions on this and the idea of putting fake KVs with the highest timestamp
of the StoreFile in the scanner priority queue.
bq.
bq.
bq. This addresses bug HBASE-4465.
bq. https://issues.apache.org/jira/browse/HBASE-4465
bq.
bq.
bq. Diffs
bq. -----
bq.
bq. src/main/java/org/apache/hadoop/hbase/KeyValue.java aa34006
bq.
src/main/java/org/apache/hadoop/hbase/regionserver/AbstractKeyValueScanner.java
94ddce7
bq. src/main/java/org/apache/hadoop/hbase/regionserver/ColumnCount.java
1be0280
bq. src/main/java/org/apache/hadoop/hbase/regionserver/KeyValueHeap.java
b8d33e8
bq. src/main/java/org/apache/hadoop/hbase/regionserver/KeyValueScanner.java
fbcd276
bq. src/main/java/org/apache/hadoop/hbase/regionserver/MemStore.java 035f765
bq.
src/main/java/org/apache/hadoop/hbase/regionserver/NonLazyKeyValueScanner.java
PRE-CREATION
bq. src/main/java/org/apache/hadoop/hbase/regionserver/ScanQueryMatcher.java
dad278a
bq. src/main/java/org/apache/hadoop/hbase/regionserver/StoreFile.java
abb5931
bq. src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileScanner.java
31bfea7
bq. src/main/java/org/apache/hadoop/hbase/regionserver/StoreScanner.java
64a6e3e
bq. src/main/java/org/apache/hadoop/hbase/util/CollectionBackedScanner.java
8ad5aab
bq. src/test/java/org/apache/hadoop/hbase/regionserver/TestMemStore.java
9d2b2a7
bq.
bq. Diff: https://reviews.apache.org/r/2180/diff
bq.
bq.
bq. Testing
bq. -------
bq.
bq. Running unit tests -- please do not commit yet.
bq.
bq.
bq. Thanks,
bq.
bq. Mikhail
bq.
bq.
> Lazy-seek optimization for StoreFile scanners
> ---------------------------------------------
>
> Key: HBASE-4465
> URL: https://issues.apache.org/jira/browse/HBASE-4465
> Project: HBase
> Issue Type: Improvement
> Reporter: Mikhail Bautin
> Assignee: Mikhail Bautin
> Labels: optimization, seek
> Fix For: 0.89.20100924, 0.94.0
>
>
> Previously, if we had several StoreFiles for a column family in a region, we
> would seek in each of them and only then merge the results, even though the
> row/column we are looking for might only be in the most recent (and the
> smallest) file. Now we prioritize our reads from those files so that we check
> the most recent file first. This is done by doing a "lazy seek" which
> pretends that the next value in the StoreFile is (seekRow, seekColumn,
> lastTimestampInStoreFile), which is earlier in the KV order than anything
> that might actually occur in the file. So if we don't find the result in
> earlier files, that fake KV will bubble up to the top of the KV heap and a
> real seek will be done. This is expected to significantly reduce the amount
> of disk IO (as of 09/22/2011 we are doing dark launch testing and
> measurement).
> This is joint work with Liyin Tang -- huge thanks to him for many helpful
> discussions on this and the idea of putting fake KVs with the highest
> timestamp of the StoreFile in the scanner priority queue.
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