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https://issues.apache.org/jira/browse/HBASE-3562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13011175#comment-13011175
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Evert Arckens commented on HBASE-3562:
--------------------------------------
In ScanQueryMatcher.match I would do the columns.checkColumn call first and
only if that returns MatchCode.INCLUDE execute the filters. I think this would
be more efficient as well since calculating to skip a column or not will
usually be faster than evaluating one ore more filters.
However, in the code is mentioned explicitly :
/**
* Filters should be checked before checking column trackers. If we do
* otherwise, as was previously being done, ColumnTracker may increment its
* counter for even that KV which may be discarded later on by Filter. This
* would lead to incorrect results in certain cases.
*/
It is not completely clear to me what the exact purpose of the counter on the
ColumnTracker is or what the problem would be if it was incremented.
Maybe calling ((ExplicitColumnTracker)columns).doneWithColumn (like is done in
getNextRowOrNextColumn) explicitly when a filter skips a column can help here?
> ValueFilter is being evaluated before performing the column match
> -----------------------------------------------------------------
>
> Key: HBASE-3562
> URL: https://issues.apache.org/jira/browse/HBASE-3562
> Project: HBase
> Issue Type: Bug
> Components: filters
> Affects Versions: 0.90.0
> Reporter: Evert Arckens
>
> When performing a Get operation where a both a column is specified and a
> ValueFilter, the ValueFilter is evaluated before making the column match as
> is indicated in the javadoc of Get.setFilter() : " {@link
> Filter#filterKeyValue(KeyValue)} is called AFTER all tests for ttl, column
> match, deletes and max versions have been run. "
> The is shown in the little test below, which uses a TestComparator extending
> a WritableByteArrayComparable.
> public void testFilter() throws Exception {
> byte[] cf = Bytes.toBytes("cf");
> byte[] row = Bytes.toBytes("row");
> byte[] col1 = Bytes.toBytes("col1");
> byte[] col2 = Bytes.toBytes("col2");
> Put put = new Put(row);
> put.add(cf, col1, new byte[]{(byte)1});
> put.add(cf, col2, new byte[]{(byte)2});
> table.put(put);
> Get get = new Get(row);
> get.addColumn(cf, col2); // We only want to retrieve col2
> TestComparator testComparator = new TestComparator();
> Filter filter = new ValueFilter(CompareOp.EQUAL, testComparator);
> get.setFilter(filter);
> Result result = table.get(get);
> }
> public class TestComparator extends WritableByteArrayComparable {
> /**
> * Nullary constructor, for Writable
> */
> public TestComparator() {
> super();
> }
>
> @Override
> public int compareTo(byte[] theirValue) {
> if (theirValue[0] == (byte)1) {
> // If the column match was done before evaluating the filter, we
> should never get here.
> throw new RuntimeException("I only expect (byte)2 in col2, not
> (byte)1 from col1");
> }
> if (theirValue[0] == (byte)2) {
> return 0;
> }
> else return 1;
> }
> }
> When only one column should be retrieved, this can be worked around by using
> a SingleColumnValueFilter instead of the ValueFilter.
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