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Re: sqlite3 timing

From: Daniel Shahaf <d.s_at_daniel.shahaf.name>
Date: Thu, 14 Jul 2011 06:14:35 +0300

Nothing to see here. (The syntax I used doesn't have the semantics
I expected it to have.)

Daniel Shahaf wrote on Thu, Jul 14, 2011 at 05:53:52 +0300:
> From my shell session:
>
> [[[
> % time sqlite3 foo.db "SELECT hash, revision, offset, size, expanded_size FROM rep_cache;" > /dev/null
> sqlite3 foo.db > /dev/null 12.72s user 0.69s system 98% cpu 13.575 total
>
> % time sqlite3 foo.db "SELECT hash, revision, offset, size, expanded_size FROM rep_cache;" > /dev/null
> sqlite3 foo.db > /dev/null 12.56s user 0.94s system 99% cpu 13.561 total
>
> % time sqlite3 foo.db "SELECT hash, revision, offset, size, expanded_size, COUNT(*) FROM rep_cache;" > /dev/null
> sqlite3 foo.db > /dev/null 2.76s user 0.72s system 99% cpu 3.492 total
>
> % time sqlite3 foo.db "SELECT hash, revision, offset, size, expanded_size, COUNT(*) FROM rep_cache;" > /dev/null
> sqlite3 foo.db > /dev/null 2.79s user 0.69s system 99% cpu 3.498 total
>
> % time sqlite3 foo.db "SELECT hash, revision, offset, size, expanded_size FROM rep_cache;" > /dev/null
> sqlite3 foo.db > /dev/null 12.62s user 0.75s system 99% cpu 13.430 total
>
> % sqlite3 -version
> 3.7.4
> ]]]
>
> That is: adding COUNT(*) to the query makes it 3.9 times faster.
>
> Huh? How does that make sense? Should we do anything differently in
> our code in light of this?
>
>
> [ This isn't a fabricated example --- this is the query I added to
> rep-cache.c today ]
Received on 2011-07-14 05:15:41 CEST

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