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HBase, mail # dev - Scanner with explicit columns list is very slow


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Re: Scanner with explicit columns list is very slow
Vladimir Rodionov 2013-10-14, 21:03
I modified tests:

Now I created table with one CF and 5 columns: CQ1,..,CQ5

1. Scan.addColumn(CF, CQ1);
    Scan.addColumn(CF, CQ3);

2. Scan.addFamily(CF);

Scan performance from block cache:

1.  400K rows per sec
2.  1.6M rows per sec

The explicit columns scan performance  is even worse in this case. It is
much faster to scan the WHOLE rows and filter columns later in a Filter,
than specify columns directly in a Scan.

Definitely needs to be explained/investigated.
On Mon, Oct 14, 2013 at 11:18 AM, Vladimir Rodionov <[EMAIL PROTECTED]
> wrote:

> Its 0.94.6 and there is chance that the issue has been fixed already
>
> Simple table: one column + one qualifier
>
> Two type of scans:
>
> 1. Scan.addFamily(CF)
>
> 2. Scan.addColumn(CF, CQ)
>
> Both run on block cache (all data in memory)
>
> Tested on StoreScanner directly.
>
> 1. 4.2M KVs per sec per one thread
> 2. 1.5M KVs per second per one thread.
>
> The difference? First scanner's ScanQueryMatcher returns INCLUDE, DONE,
> second - INCLUDE_NEXT_ROW, DONE
> The cost of Row's reseek is huge.
>
> Best regards,
> Vladimir Rodionov
> Principal Platform Engineer
> Carrier IQ, www.carrieriq.com
> e-mail: [EMAIL PROTECTED]
>
>
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