From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
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To: | PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org> |
Subject: | New setval() call |
Date: | 2001-02-10 17:23:52 |
Message-ID: | 200102101723.MAA04962@candle.pha.pa.us |
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Lists: | pgsql-hackers |
I am inclinded to remove this open item:
New SQL function setval(seq,val,bool) for use in pg_dump (Philip)
The use of the 3rd parameter, 'iscalled', while used by pg_dump, is not
of general use, so we probably don't need to document it. Is this valid?
Info on the new param is:
---------------------------------------------------------------------------
IRC the point of the nextval() is to ensure that the internal state of
the sequence is correct. There's a bool "is_called" in the sequence
that means something like "I've been nextval()'d at least once", and the
only clean way to make that become set is to issue a nextval. You can
watch the behavior by doing "select * from sequenceobject" between
sequence commands --- it looks like the first nextval() simply sets
is_called without changing last_value, and then subsequent nextval()s
increment last_value. (This peculiar arrangement makes it possible
to have a starting value equal to MININT, should you want to do so.)
So pg_dump needs to make sure it restores the correct setting of both
fields.
This is pretty grotty because it looks like there's no way to clear
is_called again, short of dropping and recreating the sequence.
So unless you want to do that always, a data-only restore couldn't
guarantee to restore the state of a virgin sequence.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
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