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https://issues.apache.org/jira/browse/HBASE-5104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13181053#comment-13181053
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Lars Hofhansl commented on HBASE-5104:
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It seems you have a very specific usecase. A limit/offset API that is column
based on an API that is inherently row based (scanner.next) will be hard to
understand for users.
The problem here seems to be that scanner.startRow and scanner.next do not
provide enough granularity.
I'm not opposed to limit/offset (but I will be interested to see how you will
document that API, to make is understandable to users :) ).
What about a nextColumn method on scanner along with a startColumn method?
Anyway... I just want to make sure we do not add API for specific cases, and
I'll shut up about it now.
> Provide a reliable intra-row pagination mechanism
> -------------------------------------------------
>
> Key: HBASE-5104
> URL: https://issues.apache.org/jira/browse/HBASE-5104
> Project: HBase
> Issue Type: Bug
> Reporter: Kannan Muthukkaruppan
> Assignee: Madhuwanti Vaidya
> Attachments: testFilterList.rb
>
>
> Addendum:
> Doing pagination (retrieving at most "limit" number of KVs at a particular
> "offset") is currently supported via the ColumnPaginationFilter. However, it
> is not a very clean way of supporting pagination. Some of the problems with
> it are:
> * Normally, one would expect a query with (Filter(A) AND Filter(B)) to have
> same results as (query with Filter(A)) INTERSECT (query with Filter(B)). This
> is not the case for ColumnPaginationFilter as its internal state gets updated
> depending on whether or not Filter(A) returns TRUE/FALSE for a particular
> cell.
> * When this Filter is used in combination with other filters (e.g., doing AND
> with another filter using FilterList), the behavior of the query depends on
> the order of filters in the FilterList. This is not ideal.
> * ColumnPaginationFilter is a stateful filter which ends up counting multiple
> versions of the cell as separate values even if another filter upstream or
> the ScanQueryMatcher is going to reject the value for other reasons.
> Seems like we need a reliable way to do pagination. The particular use case
> that prompted this JIRA is pagination within the same rowKey. For example,
> for a given row key R, get columns with prefix P, starting at offset X (among
> columns which have prefix P) and limit Y. Some possible fixes might be:
> 1) enhance ColumnPrefixFilter to support another constructor which supports
> limit/offset.
> 2) Support pagination (limit/offset) at the Scan/Get API level (rather than
> as a filter) [Like SQL].
> Original Post:
> Thanks Jiakai Liu for reporting this issue and doing the initial
> investigation. Email from Jiakai below:
> Assuming that we have an index column family with the following entries:
> "tag0:001:thread1"
> ...
> "tag1:001:thread1"
> "tag1:002:thread2"
> ...
> "tag1:010:thread10"
> ...
> "tag2:001:thread1"
> "tag2:005:thread5"
> ...
> To get threads with "tag1" in range [5, 10), I tried the following code:
> ColumnPrefixFilter filter1 = new
> ColumnPrefixFilter(Bytes.toBytes("tag1"));
> ColumnPaginationFilter filter2 = new ColumnPaginationFilter(5 /* limit
> */, 5 /* offset */);
> FilterList filters = new FilterList(Operator.MUST_PASS_ALL);
> filters.addFilter(filter1);
> filters.addFilter(filter2);
> Get get = new Get(USER);
> get.addFamily(COLUMN_FAMILY);
> get.setMaxVersions(1);
> get.setFilter(filters);
> Somehow it didn't work as expected. It returned the entries as if the filter1
> were not set.
> Turns out the ColumnPrefixFilter returns SEEK_NEXT_USING_HINT in some cases.
> The FilterList filter does not handle this return code properly (treat it as
> INCLUDE).
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