The following bug has been logged on the website:
Bug reference: 7648
Logged by: Daniel Farina
Email address: daniel@heroku.com
PostgreSQL version: 9.0.9
Operating system: Ubuntu 10.04
Description: =
At more or less one point in time exactly (the same second, at minimum), a
couple of errors were raised on a hot standby while performing query access
that would nominally suggest corruption were raised:
PGError: ERROR: could not read block 556642 in file "base/16385/2904143.4":
read only 0 of 8192 =
Immediately thereafter, no occurrences of the error resurfaced and any
attempts to reproduce the issue with an identical query were met with
failure.
On investigation, this relfile is a fairly common beast: an integer btree
index being used for row identification (e.g. serial).
This is reading from a 9.0.8 Postgres.