Alexandra Nitzschke <an@clickware.de> writes:
> We have had a look at the /var/log files, no system crash, kernel panic or messages like this has happened.
What this smells like is a failed page split --- somewhere in the index
there is a down-link pointing at page 77, but page 77 didn't actually
get added to the file.
If there was no system crash or hardware misfeasance then that'd
represent a Postgres bug, but it's difficult to do much about it
unless you can come up with a reproducible sequence to trigger the bug.
(Also, since you didn't mention otherwise, I assume this is a btree
index?)
regards, tom lane