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https://issues.apache.org/jira/browse/HBASE-2794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12887443#action_12887443
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HBase Review Board commented on HBASE-2794:
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Message from: "Kris Jirapinyo" <[email protected]>
bq. On 2010-07-12 10:17:25, Nicolas wrote:
bq. >
/trunk/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFile.java, line
860
bq. > <http://review.hbase.org/r/296/diff/1/?file=2378#file2378line860>
bq. >
bq. > probably should pre-allocate the ArrayList() size so we only deal
with one heap element.
Good idea.
bq. On 2010-07-12 10:17:25, Nicolas wrote:
bq. >
/trunk/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFile.java, line
857
bq. > <http://review.hbase.org/r/296/diff/1/?file=2378#file2378line857>
bq. >
bq. > have you done any tests to see when the number of bloom checks takes
significant time compared to just getting the block? For example, if you have
100 columns to lookup, do bloom filters really buy you anything, or shouldn't
you just switch to a Row-level bloom anyways? Also, with a default 1% error
rate, you're looking at ~100% false positive with 100 columns. Maybe
max.columns = sqrt(1/error.rate)
I have not, but would running on just the test data be sufficent to tell the
true savings since the tests just run on mock data? I don't really have a dev
cluster with real data that I can test this on, so perhaps you or someone could
help out in that regard.
- Kris
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> ROWCOL bloom filter not used if multiple columns within same family are
> requested in a Get
> ------------------------------------------------------------------------------------------
>
> Key: HBASE-2794
> URL: https://issues.apache.org/jira/browse/HBASE-2794
> Project: HBase
> Issue Type: Improvement
> Reporter: Kannan Muthukkaruppan
> Attachments: 2794_multi_column_check.txt
>
>
> Noticed the following snippet in StoreFile.java:Scanner:shouldSeek():
> {code}
> switch(bloomFilterType) {
> case ROW:
> key = row;
> break;
> case ROWCOL:
> if (columns.size() == 1) {
> byte[] col = columns.first();
> key = Bytes.add(row, col);
> break;
> }
> //$FALL-THROUGH$
> default:
> return true;
> }
> {code}
> If columns.size > 1, then we currently don't take advantage of the bloom
> filter. We should optimize this to check bloom for each of columns and if
> none of the columns are present in the bloom avoid opening the file.
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