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From "Matteo Bertozzi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14283) Reverse scan doesn’t work with HFile inline index/bloom blocks
Date Sat, 26 Sep 2015 01:58:05 GMT

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Matteo Bertozzi commented on HBASE-14283:
-----------------------------------------

v4 probably is a bad name.. 
this is more a v2/3.x since (the original idea) was just a fix in the format to solve a bug.
not a complete format redesign. everything should be the same aside adding one field on the
level block. 
Ben was also suggesting a double rolling upgrade to migrate to that, more or less like we
did for 3.
I'm ok to have it only in 2.0, but to me this can also be done in a 1.3. just switch the name
from v4 to 3.x :)

if we want to extend the scope of redesigning the file-format, that will be another topic.
I know that [~lhofhansl], during hbasecon, was suggesting format changes to group by qualifiers
and similar.
but that will not be just related to fixing this bug and it will probably be in 2.0 only I
guess.

> Reverse scan doesn’t work with HFile inline index/bloom blocks
> --------------------------------------------------------------
>
>                 Key: HBASE-14283
>                 URL: https://issues.apache.org/jira/browse/HBASE-14283
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Ben Lau
>            Assignee: Ben Lau
>         Attachments: HBASE-14283-v2.patch, HBASE-14283.patch, hfile-seek-before.patch
>
>
> Reverse scans do not work if an HFile contains inline bloom blocks or leaf level index
blocks.  The reason is because the seekBefore() call calculates the previous data block’s
size by assuming data blocks are contiguous which is not the case in HFile V2 and beyond.
> Attached is a first cut patch (targeting bcef28eefaf192b0ad48c8011f98b8e944340da5 on
trunk) which includes:
> (1) a unit test which exposes the bug and demonstrates failures for both inline bloom
blocks and inline index blocks
> (2) a proposed fix for inline index blocks that does not require a new HFile version
change, but is only performant for 1 and 2-level indexes and not 3+.  3+ requires an HFile
format update for optimal performance.    
> This patch does not fix the bloom filter blocks bug.  But the fix should be similar to
the case of inline index blocks.  The reason I haven’t made the change yet is I want to
confirm that you guys would be fine with me revising the HFile.Reader interface.
> Specifically, these 2 functions (getGeneralBloomFilterMetadata and getDeleteBloomFilterMetadata)
need to return the BloomFilter.  Right now the HFileReader class doesn’t have a reference
to the bloom filters (and hence their indices) and only constructs the IO streams and hence
has no way to know where the bloom blocks are in the HFile.  It seems that the HFile.Reader
bloom method comments state that they “know nothing about how that metadata is structured”
but I do not know if that is a requirement of the abstraction (why?) or just an incidental
current property. 
> We would like to do 3 things with community approval:
> (1) Update the HFile.Reader interface and implementation to contain and return BloomFilters
directly rather than unstructured IO streams
> (2) Merge the fixes for index blocks and bloom blocks into open source
> (3) Create a new Jira ticket for open source HBase to add a ‘prevBlockSize’ field
in the block header in the next HFile version, so that seekBefore() calls can not only be
correct but performant in all cases.



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