Re: failure with pg_dump

Mija Lee <mija@scharp.org> writes:
> I have a script that I use to do regular dumps of my database. Over the
> weekend it failed, and produced the following error message. I'm not
> sure why this would have happened, how I would find out which index is
> referenced by 136451098, or where this select came from.

It sounds like system catalog corruption, which is not good :-(.

> pg_dump.sqlhost: Error message from server: ERROR:  cache lookup failed
> for index 136451098
> pg_dump.sqlhost: The command was: SELECT t.tableoid, t.oid, t.relname as
> indexname, pg_catalog.pg_get_indexdef(i.indexrelid) as indexdef,
> t.relnatts as indnkeys, i.indkey, i.indisclustered, c.contype,
> c.conname, c.tableoid as contableoid, c.oid as conoid, (SELECT spcname
> FROM pg_catalog.pg_tablespace s WHERE s.oid = t.reltablespace) as
> tablespace, array_to_string(t.reloptions, ', ') as options FROM
> pg_catalog.pg_index i JOIN pg_catalog.pg_class t ON (t.oid =
> i.indexrelid) LEFT JOIN pg_catalog.pg_depend d ON (d.classid =
> t.tableoid AND d.objid = t.oid AND d.deptype = 'i') LEFT JOIN
> pg_catalog.pg_constraint c ON (d.refclassid = c.tableoid AND d.refobjid
> = c.oid) WHERE i.indrelid = '136451090'::pg_catalog.oid ORDER BY indexname

That looks like pg_dump's query to get information about the indexes of
a particular table.  So apparently the problem index is one of the ones
for the table with OID 136451090.  The easiest way to find out which one
that is is
    select '136451090'::regclass;
Trying \d on each of that table's indexes in succession would tell you
which one is trashed.

As for fixing it, the $64 question is how extensive is the catalog
corruption.  I see no very good reason to hope that only this one index
is affected :-(.  What you probably want to do is try to get a clean
pg_dump then initdb and reload --- at least that's how I'd approach it,
rather than hoping that there's no lurking problems remaining after you
hack your way around the one you can see.

What I'd try first is a REINDEX on pg_class.  If that doesn't help,
try to delete the pg_index row linking 136451098 and 136451090.

What PG version is this, anyway, and did anything weird happen on your
system that might explain data corruption?

            regards, tom lane