Pg_xactlock is always there as a special relation. It has no footprint on
disk. Transactions will keep a record in pg_xactlock at the beginning and
remove the record at the end. Once any conflicting update happens, the
latter transaction will use this relation to wait for the former
transaction's result. AFAIK, since lock tag always needs a relationalId as a
parameter, so we create this special relation for this usage.
I am not sure about 'c'.
Regards,
Qingqing
"Katsuhiko Okano" <k_okano@po.ntts.co.jp> writes
> Hi.
> I'm writing backup guide and script.
>
> I will look up on-disk-filename should be backuped
> in a pg_class, like:
> >SELECT oid,relfilenode,relname,relkind FROM pg_class;
> it return like:
> > 17173 | 17173 | sql_packages | r
> > 17182 | 17182 | pg_toast_17178_index | i
> > 17180 | 17180 | pg_toast_17178 | t
> > 376 | 0 | pg_xactlock | s
>
> I'll include backup set relkind='r' or 'i' or 'S' or 'v' or 't'.
> but PostgreSQL 8.0.1 Documentation "41.9. pg_class" say
> >c = composite type, s = special
>
> 1)relkind = 's' is always have not on-disk file?
>
> 2)when exist relkind='s' object except pg_xactlock?
> user(administrator) can create it?
>
> 3)relkind = 'c' is always have not on-disk file?
> (I create TYPE. but no file exist.)
> I will only include pg_type relation in backup set. is it OK ?
>
> 4)any other advice to backup? :-)
>
>
> Regards,
> --
> ----------------------------------------
> Katsuhiko Okano
> k_okano _at_ po.ntts.co.jp
> NTT Software Corp. (division "NBRO-PT6")
>
>
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