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https://issues.apache.org/jira/browse/HBASE-17125?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16056932#comment-16056932
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Duo Zhang commented on HBASE-17125:
-----------------------------------
And I need to say again, we have never break the javadoc of setMaxVersions. If
you do not use filtr, then the behavior is correct. If you use filter, then
this is what the javadoc of setFilter says, filter is tested at last.
{quote}
/**
* Apply the specified server-side filter when performing the Query.
* Only {@link Filter#filterKeyValue(org.apache.hadoop.hbase.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
*/
{quote}
Filter always introduces behaviors which are not intuitive because it is too
flexible. For example, PageFilter may still return more rows than configured.
You need to know the details of HBase if you want to use filter correctly.
That's why I want to fix the problem in a simpler way rather than a complicated
way. It does not make any big difference to users. For normal users they just
do not care, and for advanced users they must know the implementation details.
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
> Assignee: Guanghao Zhang
> Priority: Critical
> Fix For: 2.0.0
>
> Attachments: example.diff, HBASE-17125.master.001.patch,
> HBASE-17125.master.002.patch, HBASE-17125.master.002.patch,
> HBASE-17125.master.003.patch, HBASE-17125.master.004.patch,
> HBASE-17125.master.005.patch, HBASE-17125.master.006.patch,
> HBASE-17125.master.007.patch, HBASE-17125.master.008.patch,
> HBASE-17125.master.009.patch, HBASE-17125.master.009.patch,
> HBASE-17125.master.010.patch, HBASE-17125.master.011.patch
>
>
> 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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