On Wed, Jan 19, 2011 at 2:58 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Wed, Jan 19, 2011 at 12:10 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> Robert Haas <robertmh...@gmail.com> writes: >>>> Yeah. Many-times-repeated detoasting is really bad, and this is not >>>> the only place in the backend where we have this problem. :-( > >>> Yeah, there's been some discussion of a more general solution, and I >>> think I even had a trial patch at one point (which turned out not to >>> work terribly well, but maybe somebody will have a better idea someday). > >> I'm pretty doubtful that there's going to be a general solution to >> this problem - I think it's going to require gradual refactoring of >> problem spots. > > Do you remember the previous discussion? One idea that was on the table > was to make the TOAST code maintain a cache of detoasted values, which > could be indexed by the toast pointer OIDs (toast rel OID + value OID), > and then PG_DETOAST_DATUM might give back a pointer into the cache > instead of a fresh value. In principle that could be done in a fairly > centralized way. The hard part is to know when a cache entry is not > actively referenced anymore ...
I do remember that discussion. Aside from the problem you mention, it also seems that maintaining the hash table and doing lookups into it would have some intrinsic cost. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
