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Re: Largeobject Access Controls (r2460)

From: Takahiro Itagaki <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>
To: KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, KaiGai Kohei <kaigai(at)kaigai(dot)gr(dot)jp>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jaime Casanova <jcasanov(at)systemguards(dot)com(dot)ec>, Greg Smith <greg(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Largeobject Access Controls (r2460)
Date: 2010-02-09 11:16:07
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Lists: pgsql-hackers
KaiGai Kohei <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:

> > I don't think this is necessarily a good idea.  We might decide to treat
> > both things separately in the future and it having them represented
> > separately in the dump would prove useful.
> I agree. From design perspective, the single section approach is more
> simple than dual section, but its change set is larger than the dual.


When I tested a custom dump with pg_restore, --clean & --single-transaction
will fail with the new dump format because it always call lo_unlink()
even if the large object doesn't exist. It comes from dumpBlobItem:

! dumpBlobItem(Archive *AH, BlobInfo *binfo)
! 	appendPQExpBuffer(dquery, "SELECT lo_unlink(%s);\n", binfo->;

The query in DropBlobIfExists() could avoid errors -- should we use it here?
| SELECT lo_unlink(oid) FROM pg_largeobject_metadata WHERE oid = %s;

BTW, --clean option is ambiguous if combined with --data-only. Restoring
large objects fails for the above reason if previous objects don't exist,
but table data are restored *without* truncation of existing data. Will
normal users expect TRUNCATE-before-load for --clean & --data-only cases?

    Present behaviors are;
        Table data    - Appended. (--clean is ignored)
        Large objects - End with an error if object doesn't exist.
    IMO, ideal behaviors are:
        Table data    - Truncate existing data and load new ones.
        Large objects - Work like as MERGE (or REPLACE, UPSERT).


Takahiro Itagaki
NTT Open Source Software Center

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