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https://issues.apache.org/jira/browse/HBASE-17125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15701045#comment-15701045
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Duo Zhang commented on HBASE-17125:
-----------------------------------
HBASE-13094 aims to add a new type of filter right? This issue aims to solve
the problem for the current fiter implementation.
And I need to speak again, the old 'filter then check verions' is not stable.
The same request can return different results only if there is a major
compaction. This is a bug and we need to fix it.
And the biggest problem here, is the semantic of setMaxVerions. In the javadoc
of setFilter method, the max versions check should be evaluated before
filtering but the current implementation is more likely a limitation of the
final result. This leads to two approaches to fix the bug, one is try to break
our javadoc and the new implementation will be more complicated, but can keep
compatible with the old implementation as much as possible. The other is to
change the implementation according to our javadoc, the fix is simple and
straight-forward.
Thanks.
> Inconsistent result when use filter to read data
> ------------------------------------------------
>
> Key: HBASE-17125
> URL: https://issues.apache.org/jira/browse/HBASE-17125
> Project: HBase
> Issue Type: Bug
> Reporter: Guanghao Zhang
> Attachments: example.diff
>
>
> Assume a cloumn's max versions is 3, then we write 4 versions of this column.
> The oldest version doesn't remove immediately. But from the user view, the
> oldest version has gone. When user use a filter to query, if the filter skip
> a new version, then the oldest version will be seen again. But after compact
> the region, then the oldest version will never been seen. So it is weird for
> user. The query will get inconsistent result before and after region
> compaction.
> The reason is matchColumn method of UserScanQueryMatcher. It first check the
> cell by filter, then check the number of versions needed. So if the filter
> skip the new version, then the oldest version will be seen again when it is
> not removed.
> Have a discussion offline with [~Apache9] and [~fenghh], now we have two
> solution for this problem. The first idea is check the number of versions
> first, then check the cell by filter. As the comment of setFilter, the filter
> is called after all tests for ttl, column match, deletes and max versions
> have been run.
> {code}
> /**
> * Apply the specified server-side filter when performing the Query.
> * Only {@link Filter#filterKeyValue(Cell)} is called AFTER all tests
> * for ttl, column match, deletes and max versions have been run.
> * @param filter filter to run on the server
> * @return this for invocation chaining
> */
> public Query setFilter(Filter filter) {
> this.filter = filter;
> return this;
> }
> {code}
> But this idea has another problem, if a column's max version is 5 and the
> user query only need 3 versions. It first check the version's number, then
> check the cell by filter. So the cells number of the result may less than 3.
> But there are 2 versions which don't read anymore.
> So the second idea has three steps.
> 1. check by the max versions of this column
> 2. check the kv by filter
> 3. check the versions which user need.
> But this will lead the ScanQueryMatcher more complicated. And this will break
> the javadoc of Query.setFilter.
> Now we don't have a final solution for this problem. Suggestions are welcomed.
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