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HBase, mail # user - Scans and Bloom Filter


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Re: Scans and Bloom Filter
Nicolas Spiegelberg 2012-02-16, 20:52
Bryan,

Currently, ROW & ROWCOL Bloom Filters are only checked for explicit,
single-row 'Get' scans.  ROWCOL BFs are only checked when you're querying
for explicit column qualifiers (vs getting the entire row).  This is
because multi-row scans & full-row scans are implicit queries.  To
clarify:

With a multirow scan, the next row after 0x0001 is NOT 0x0002.  HBase only
knows that the next row is > 0x0001.  The next row could be 0x00010 or
0x0003.  However, when you call Htable.get(row=0x0001), HBase knows that
you explicitly want that row and don't want 0x00010.

Nicolas

On 2/15/12 9:18 PM, "Bryan Beaudreault" <[EMAIL PROTECTED]> wrote:

>Hello,
>
>We are looking at Bloom Filters and wondering if they are helpful when
>doing a sequential read (multi-row scan) or only when doing a Get for a
>single row.  It logically makes sense that it would only affect (or to
>greater affect) getting a single row since it is a way for determining if
>you have to read a whole store file when fetching a key.  But, we are told
>that Scan and Get are essentially the same code on the backend, so I
>imagine both will check the Blooms if they exist.
>
>Also, would a ROWCOL bloom be more effective if you are often doing
>multi-row scans but always with specifying only a subset of columns in
>those rows?
>
>Thanks,
>
>Bryan