| From: | "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com> |
|---|---|
| To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql(at)mohawksoft(dot)com, "Hannu Krosing" <hannu(at)2ndquadrant(dot)com>, Decibel! <decibel(at)decibel(dot)org>, "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, "Pg Hackers" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Block-level CRC checks |
| Date: | 2008-10-01 15:21:13 |
| Message-ID: | 36e682920810010821l381f569wed7ab2a60bc0ad1d@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Oct 1, 2008 at 10:27 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I don't think that the amount of time it would take to calculate and test
>> the sum is even important. It may be in older CPUs, but these days CPUs
>> are so fast in RAM and a block is very small. On x86 systems, depending on
>> page alignment, we are talking about two or three pages that will be "in
>> memory" (They were used to read the block from disk or previously
>> accessed).
>
> Your optimism is showing ;-). XLogInsert routinely shows up as a major
> CPU hog in any update-intensive test, and AFAICT that's mostly from the
> CRC calculation for WAL records.
I probably wouldn't compare checksumming *every* WAL record to a
single block-level checksum.
--
Jonah H. Harris, Senior DBA
myYearbook.com
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