RE: [HACKERS] double opens

> 
> [Charset iso-8859-1 unsupported, filtering to ASCII...]
> > Hi all,
> > 
> > There is a TODO item
> > * Overhaul mdmgr/smgr to fix double unlinking and double opens, cleanup
> > 
> > In Windows-NT,we could see the following error reported by 
> > yutaka tanida [yutaka@marin.or.jp]. 
> > 
> > > version
> > > ------------------------------------------------------------
> > > PostgreSQL 6.5.1 on i686-pc-cygwin, compiled by gcc gcc-2.95
> > > (1 row)
> > >
> > > template1=> create table table1 ( i int,j int);
> > > CREATE
> > > template1=> create view view1 as select * from table1;
> > > CREATE
> > > template1=> drop view view1;
> > > DROP
> > > template1=> create view view1 as select * from table1;
> > > ERROR:  cannot create view1
> > 
> > "drop view" couldn't unlink the base file of target view because
> > it is doubly opened and so "create view" coundn't create the view. 
> >
[snip]

> > 
> > *** utils/cache/relcache.c.orig    Wed May 26 16:05:38 1999
> > --- utils/cache/relcache.c    Wed Jul 28 13:23:49 1999
> > ***************
> > *** 1282,1287 ****
> > --- 1282,1288 ----
> >           oldcxt = MemoryContextSwitchTo((MemoryContext) CacheCxt);
> >   
> >           RelationCacheDelete(relation);
> > +         smgrclose(DEFAULT_SMGR, relation);
> >   
> >           FreeTupleDesc(relation->rd_att);
> >           SystemCacheRelationFlushed(RelationGetRelid(relation));
> > 
> > 
> > 
> 
> Basically, I thought the close was done already in the drop table code. 
> Is it strange to do the close inside the cache?  The cache does the
> opens, right?
>

No,relcache stuff doesn't do the opens.

First,my patch is not only for "drop view"  case.
It's for cases such that  A backend registers an information to invalidate a relcache   entry and another backend
removesthe relcache entry trig-  gered by the information.
 

"drop view" plays both of the part alone and doubly opens
as follows.

RemoveView() RemoveRewriteRule()   prs2_deleteFromRelation()      heap_open(relid of view) ----  opens a new file
descriptor            for the base file of the view        setRelhasrulesInRelations()          heap_replace(tuple of
"pg_class")---- registers an informat-                ion to invalidate the view's                 relcache entry.
heap_close()---- doesn't close the file descriptor CommandCounterIncrement()      .................
RelationFlushRelation()--- removes the relcache entry                   of the view heap_destroy_with_catalog()
heap_openr(viewName)--- opens another file descriptor                for the same view because
heap_openr()couldn't find the                relcache entry
 

Regards.

Hiroshi Inoue
Inoue@tpf.co.jp