| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Magnus Hagander <magnus(at)hagander(dot)net> |
| Cc: | Greg Stark <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Daniel Gustafsson <daniel(at)yesql(dot)se> |
| Subject: | Re: Online enabling of checksums |
| Date: | 2018-02-28 17:06:39 |
| Message-ID: | CA+TgmoZcbkvZp=ZpWnGAxnSWbdCEw7qKPBWw-TMs9rf7waVg1A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sun, Feb 25, 2018 at 9:54 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> Also if that wasn't clear -- we only do the full page write if there isn't
> already a checksum on the page and that checksum is correct.
Hmm.
Suppose that on the master there is a checksum on the page and that
checksum is correct, but on the standby the page contents differ in
some way that we don't always WAL-log, like as to hint bits, and there
the checksum is incorrect. Then you'll enable checksums when the
standby still has some pages without valid checksums, and disaster
will ensue.
I think this could be hard to prevent if checksums are turned on and
off multiple times.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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