2017-10-06 20:39 GMT+02:00 Nico Williams <n...@cryptonector.com>: > On Fri, Oct 06, 2017 at 06:37:57PM +0200, Pavel Stehule wrote: > > 2017-10-06 6:48 GMT+02:00 Nico Williams <n...@cryptonector.com>: > > > On Fri, Oct 06, 2017 at 04:52:09AM +0200, Pavel Stehule wrote: > > > > Current TEMP tables, if you do it for any session has pretty > significant > > > > overhead - with possible risk of performance lost (system catalog > > > bloat). > > > > > > Because of the DDLs for them? > > > > yes - pg_attribute, pg_class, pg_stats are bloating - and when these > tables > > are bloated, then DDL is slow. > > :( > > > > No, I want GLOBAL TEMP tables. > > > > me too :) - and lot of customer and users. > > > I though about it, but I have other on my top priority. GLOBAL TEMP TABLE > > is on 90% unlogged table. But few fields should be session based instead > > shared persistent - statistics, rows in pg_class, filenode. > > Unlogged tables don't provide isolation between sessions the way temp > tables do, so I don't see the connection. > > But the necessary components (temp heaps and such) are all there, and I > suspect a PoC could be done fairly quickly. But there are some > subtleties like that FKs between GLOBAL TEMP and persistent tables must > not be allowed (in either direction), so a complete implementation will > take significant work. > > The work looks like: > > - add syntax (trivial) > > - add new kind of persistence (lots of places to touch, but it's mostly > mechanical) > > - redirect all references to global temp table contents to temp > heaps/indexes/whatever > > - add logic to prevent FKs between persistent and global temp tables > > - what else? > > > When we talked about this topic, there are two issues: > > > > a) probably not too hard issue - some internal data can be in session sys > > cache. > > > > b) the session sys data should be visible on SQL level too (for some > tools > > and consistency) - it is hard task. > > Can you expand on this? >
If global temporary tables should be effective, then you have not have modify system catalogue after creating. But lot of processes requires it - ANALYZE, query planning. > > Nico > -- >
