| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andrew Chernow <ac(at)esilo(dot)com> |
| Cc: | "Jonah H(dot) Harris" <jonah(dot)harris(at)gmail(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Gregory Stark <stark(at)enterprisedb(dot)com>, 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: | 2008-10-02 14:47:33 |
| Message-ID: | 29985.1222958853@sss.pgh.pa.us |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-hackers |
Andrew Chernow <ac(at)esilo(dot)com> writes:
> I read through this patch and am curious why 0xdeadbeef was used as an
> uninitialized value for the page crc. Is this value somehow less likely
> to have collisons than zero (or any other arbitrary value)?
Actually, because that's a favorite bit pattern for programs to fill
unused memory with, I'd venture that it has measurably HIGHER odds
of being bogus than any other bit pattern. Consider the possibility
that a database page got overwritten with someone's core dump.
> Would it not be better to add a boolean bit or byte to inidcate the crc
> state?
No, as noted that would give you a one-in-two chance of incorrectly
skipping the CRC check, not one-in-2^32 or so. If we're going to allow
a silent skip of the CRC check then a special value of CRC is a good way
to do it ... just not this particular one.
regards, tom lane
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Jonah H. Harris | 2008-10-02 14:48:32 | Re: Block-level CRC checks |
| Previous Message | Tom Lane | 2008-10-02 14:41:20 | Re: Block-level CRC checks |