Thread

1. Re: [HACKERS] How To free resources used by large object Relations?

   Maurice Gittens <mgittens@gits.nl> — 1998-02-22T11:51:55Z

   -----Original Message-----
   From: Vadim B. Mikheev <vadim@sable.krasnoyarsk.su>
   To: Maurice Gittens <mgittens@gits.nl>
   Cc: pgsql-hackers@postgreSQL.org <pgsql-hackers@postgreSQL.org>
   Date: zondag 22 februari 1998 17:47
   Subject: Re: [HACKERS] How To free resources used by large object Relations?
   
   
   >>
   >> Somehow I have to free the relation from the cache in the following
   >> situations:
   >> 1. In a transaction I must free the stuff when the transaction is
   >> commited/aborted.
   >
   >Backend does it, don't worry.
   I don't really understand all of the code so please bear with me.
   Could it be that large objects don't use the right  memorycontext/portals so
   that memory isn't freed automagically?
   >
   >> 2. Otherwise it must happen when lo_close is called.
   >
   >It seems that you can't remove relation from cache untill
   >commit/abort, currently: backend uses local cache to unlink
   >files of relations created in transaction if abort...
   >We could change relcache.c:RelationPurgeLocalRelation()
   >to read from pg_class directly...
   Is there a way to to tell the cache manager to free resources?
   The relations concerned are know how to properly free them is not
   however.
   >
   >But how many LO do you create in single xact ?
   Only one (in my real application).
   >Is memory allocated for cache so big ?
   Not really except that the leak accumulates as long as the connection
   with the backend is not closed.
   >
   >Vadim
   
   I have a simple test program which goes like this:
   
   (this is C-like psuedo code)
   
   main()
   {
       connection = createConnection();
   
       for(;;)
       {
           lo_create(connection,READ|WRITE);
       }
   
       destroyConnection(connection);
   }
   
   This program will leak memory each time it goes through the for loop.
   It doesn't matter if the statements in the for loop are in a transaction or
   not.
   
   When I give each large object it's own memory context (so that memory
   is freed per large object) it seems to leak memory more slowly, but it leaks
   anyway.
   
   I've tried calling a number of the functions (like
   RelationPurgeLocalRelation)
   in relcache.c to try to free up the memory myself but the backend doesn't
   like
   this (== closed connection).
   
   It looks like there is some assumption about which memorycontext/portal is
   used during transactions and that largeobjects don't obey this
   assumption.
   
   Can you make these assumptions explicite? Maybe I can then let
   large object respect these rules.
   
   Now I have the following understanding of these matters:
   1. In transactions
   All memory should be freed automatically at commit/abort.
   How do I tell the system to do it for me?
   
   2. In autocommit mode
   All resources used by large object should be freed at lo_close.
   Can I have this delayed and done automatically in the CommitTransaction
   function?
   
   3. Somehow atomic functions like lo_create should not leak memory either.
   This is the case however.
   
   Thanks for any help,
   Maurice
   
   
   

2. Re: [HACKERS] How To free resources used by large object Relations?

   Vadim Mikheev <vadim@sable.krasnoyarsk.su> — 1998-02-24T03:01:57Z

   I'm sorry, Maurice, but I haven't time to deal with this now.
   Let's 6.3 be out first...
   
   Vadim