Re: Block-level CRC checks - Mailing list pgsql-hackers

From Simon Riggs
Subject Re: Block-level CRC checks
Date
Msg-id 1224261031.3808.392.camel@ebony.2ndQuadrant
Whole thread Raw
In response to Re: Block-level CRC checks  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: Block-level CRC checks
Re: Block-level CRC checks
List pgsql-hackers
On Fri, 2008-10-17 at 12:26 -0300, Alvaro Herrera wrote:

> Apparently the only solution in sight is to WAL-log hint bits.  Simon
> opines it would be horrible from a performance standpoint to WAL-log
> every hint bit set, and I think we all agree with that.  So we need to
> find an alternative mechanism to WAL log hint bits.

Yes, it's clearly not acceptable bit by bit.

But perhaps writing a single WAL record if you scan whole page and set
all bits at once. Then it makes sense in some cases.

It might be possible to have a partial solution where some blocks have
CRC checks, some not. Most databases have static portions. Any block not
touched for X amount of time (~= to a distance between current LSN and
LSN on block) could have CRC checks added.

Or maybe just make it a table-level option and let users choose if they
want the hit or not.

Or maybe have a new command that you can run whenever you want to set
CRC checks. That way you get to choose. CHECK TABLE?

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Training, Services and Support



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