Re: WIP patch: reducing overhead for repeat de-TOASTing

Tom Lane wrote:
> OK, I've reproduced the test case locally.  I believe that when you> say "worse", you mean "worse than 8.3", right?
Andyou did tell me> offlist that you were testing with --enable-cassert.  CVS HEAD has> very substantially greater
cassertoverhead because of the> randomize_memory addition --- oprofile output for this test looks like>> samples  %
  image name               symbol name> 1239580  78.7721  postgres                 randomize_mem> 143544    9.1218
libc-2.7.so             memcpy> 48039     3.0528  libc-2.7.so              memset> 13838     0.8794  postgres
     LWLockAcquire> 12176     0.7738  postgres                 index_getnext> 11697     0.7433  postgres
LWLockRelease> 10406     0.6613  postgres                 hash_search_with_hash_value> 4739      0.3012  postgres
         toast_fetch_datum> 4099      0.2605  postgres                 _bt_checkkeys> 3905      0.2482  postgres
        AllocSetAlloc> 3751      0.2384  postgres                 PinBuffer> 3545      0.2253  postgres
UnpinBuffer>>I'm inclined to think that we'd better turn that off by default,> since it's not looking like it's
catchinganything new.
 

Yes, I suspect that's probably it. I applied the patch straight to CVS 
tip as I wasn't aware of any changes that would affect the unpatched 
result, but I was obviously wrong ;)

(cut)
> On the whole I'm still feeling pretty discouraged about this patch ...

At the very least we have some more information on how an eventual 
solution should work, and a test case to help analyse the effectiveness 
of any potential solution.


ATB,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
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