From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>, Jan Wieck <wieck(at)debis(dot)com>, pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] LONG |
Date: | 1999-12-13 03:25:54 |
Message-ID: | 199912130325.WAA14266@candle.pha.pa.us |
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Lists: | pgsql-hackers |
> "Hiroshi Inoue" <Inoue(at)tpf(dot)co(dot)jp> writes:
> > There are so many mails for me to follow about this issue.
> > For example,what's the conclusion about the following ?
>
> I don't think it's concluded yet...
>
> > Why is CTID needed ? Is it necessary to know "primary" tuples from
> > out-of-lines values ?
>
> It seems to me that the primary tuple should store CTIDs of the
> out-of-line segment(s) it's using. That way, we need no index at
> all on the expansion relation, which would clearly be a win.
That could be bad. Vacuum moving expired entries in long_ tables would
need to update the ctids in the primary relation, which would be a mess.
Also, I can see an 16MB relation using 8k of stored ctids. Entries over
16MB would be overflow, causing problems. I think an index and
tradition access will be just fine.
>
> My thought was that if the expansion tuples stored CTIDs of their
> primary tuples, then it would be practical to have VACUUM consult
> the primary tuples' xact status while vacuuming the expansion.
> That way, we'd have no need to update expansion tuples when changing
> xact status of primary tuples. But I think Jan has something else
> in mind for that.
Then you need to have a way to point back to the primary table from the
long_ table. Doesn't seem worth it.
Also, I am questioning the use of compressed for long tuples. I often
don't want some compression happening behind the scenes.
--
Bruce Momjian | http://www.op.net/~candle
maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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