Re: Transaction ID wraparound: problem and proposed solution

Philip Warner <pjw(at)rhyme(dot)com(dot)au> writes:
>> * disk space --- letting pg_log grow without bound isn't a pleasant
>> prospect either.

> Maybe this can be achieved by wrapping XID for the log file only.

How's that going to improve matters? pg_log is ground truth for XIDs;
if you can't distinguish two XIDs in pg_log, there's no point in
distinguishing them elsewhere.

> Maybe I'm really missing the amount of XID manipulation, but I'd be
> surprised if 16-byte XIDs would slow things down much.

It's not so much XIDs themselves, as that I think we'd need to widen
typedef Datum too, and that affects manipulations of *all* data types.

In any case, the prospect of a multi-gigabyte, ever-growing pg_log file,
with no way to recover the space short of dump/initdb/reload, is
awfully unappetizing for a high-traffic installation...

regards, tom lane