Skip site navigation (1) Skip section navigation (2)

Re: Block-level CRC checks

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 (view raw or flat)
Thread:
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

In response to

Responses

pgsql-hackers by date

Next:From: Alvaro HerreraDate: 2008-10-01 15:28:26
Subject: Re: Block-level CRC checks
Previous:From: Paul SchlieDate: 2008-10-01 15:03:15
Subject: Re: Block-level CRC checks

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group