Обсуждение: integer ceiling in LIMIT and OFFSET
Hi guys, What is the limit on the number of rows in a PostgreSQL table? If it's more than MAXINT, we have a problem: phppgadmin# select * from test limit 2147483648; ERROR: integer out of range Same problem with OFFSET. Chris
On Wed, 2003-10-22 at 04:01, Christopher Kings-Lynne wrote: > Hi guys, > > What is the limit on the number of rows in a PostgreSQL table? If it's > more than MAXINT, we have a problem: > > phppgadmin# select * from test limit 2147483648; > ERROR: integer out of range > > Same problem with OFFSET. I see you're point, but nobody is going to be interested in the first 2 billion rows of a table without using a cursor and having some other process do the math in the background. That said, perhaps the TODO for changing LIMIT / OFFSET to be expression based should also mention bumping them to int8.
Rod Taylor <rbt@rbt.ca> writes:
> That said, perhaps the TODO for changing LIMIT / OFFSET to be expression
> based should also mention bumping them to int8.
Can't get excited about it ... this would slow down the normal use of
the facility for what seems a completely hypothetical need.
regards, tom lane
> I see you're point, but nobody is going to be interested in the first 2 > billion rows of a table without using a cursor and having some other > process do the math in the background. You have the same problem: test=# begin; BEGIN test=# declare c cursor for select * from a; DECLARE CURSOR test=# move 2147483647 in c; MOVE 0 test=# move 2147483648 in c; ERROR: syntax error at or near "2147483648" at character 6 test=# test=# fetch absolute 2147483648 in c; ERROR: syntax error at or near "2147483648" at character 16 test=# fetch relative 2147483648 in c; ERROR: syntax error at or near "2147483648" at character 16 > That said, perhaps the TODO for changing LIMIT / OFFSET to be expression > based should also mention bumping them to int8. It is fairly hypothetical, but there are some people starting to put some rather large databases in Postgres these days. Shouldn't it at least be an unsigned integer? Chris
On Wed, 22 Oct 2003, Christopher Kings-Lynne wrote: > > I see you're point, but nobody is going to be interested in the first 2 > > billion rows of a table without using a cursor and having some other > > process do the math in the background. > > You have the same problem: > > test=# begin; > BEGIN > test=# declare c cursor for select * from a; > DECLARE CURSOR > test=# move 2147483647 in c; > MOVE 0 > test=# move 2147483648 in c; > ERROR: syntax error at or near "2147483648" at character 6 > > That said, perhaps the TODO for changing LIMIT / OFFSET to be expression > > based should also mention bumping them to int8. > > It is fairly hypothetical, but there are some people starting to put > some rather large databases in Postgres these days. Shouldn't it at > least be an unsigned integer? It can't be for move/fetch since negative numbers are meaningful, and imho it'd be fairly unintuitive for limit/offset to allow unsigned range but move/fetch to only allow signed, although at least with move/fetch multiple statements should work to get the position/count you want (breaking it up into portions of no more than maxint).
On Wed, 2003-10-22 at 10:22, Christopher Kings-Lynne wrote: > > I see you're point, but nobody is going to be interested in the first 2 > > billion rows of a table without using a cursor and having some other > > process do the math in the background. > > You have the same problem: > test=# move 2147483648 in c; > ERROR: syntax error at or near "2147483648" at character 6 You're simply not going to be interested in doing this. Fetching rows in blocks of 1 million for processing is probably the highest sane maximum. Now, if we have a problem with a cursor doing 1 million loops pulling 1 million rows each iteration then we have a problem.
On Wed, 22 Oct 2003, Tom Lane wrote: > Rod Taylor <rbt@rbt.ca> writes: > > That said, perhaps the TODO for changing LIMIT / OFFSET to be expression > > based should also mention bumping them to int8. > > Can't get excited about it ... this would slow down the normal use of > the facility for what seems a completely hypothetical need. While I'm pretty sure select * from sometable limit 2147483648 isn't gonna be common, maybe someone would be likely to do something like: select * from sometable limit 10 offset 2147483648 I wouldn't do it, but who knows what shadows lurk in men's minds?
On Wed, 2003-10-22 at 12:08, scott.marlowe wrote: > On Wed, 22 Oct 2003, Tom Lane wrote: > > > Rod Taylor <rbt@rbt.ca> writes: > > > That said, perhaps the TODO for changing LIMIT / OFFSET to be expression > > > based should also mention bumping them to int8. > > > > Can't get excited about it ... this would slow down the normal use of > > the facility for what seems a completely hypothetical need. > > While I'm pretty sure > > select * from sometable limit 2147483648 > > isn't gonna be common, maybe someone would be likely to do something like: > > select * from sometable limit 10 offset 2147483648 > I wouldn't do it, but who knows what shadows lurk in men's minds? The overhead in simply getting to that offset is going to be significant and I would place my bets against anyone attempting that. A cursor pulling small chunks of a multi-billion tuple set is probably much more common, so we should ensure those work.
Rod Taylor <rbt@rbt.ca> writes:
> A cursor pulling small chunks of a multi-billion tuple set is probably
> much more common, so we should ensure those work.
This should work ... but I haven't personally had the patience to test
it ...
regards, tom lane
On Wed, 22 Oct 2003, scott.marlowe wrote: > > > That said, perhaps the TODO for changing LIMIT / OFFSET to be expression > > > based should also mention bumping them to int8. > > > > Can't get excited about it ... this would slow down the normal use of > > the facility for what seems a completely hypothetical need. > > While I'm pretty sure > > select * from sometable limit 2147483648 > > isn't gonna be common, maybe someone would be likely to do something like: > > select * from sometable limit 10 offset 2147483648 > > I wouldn't do it, but who knows what shadows lurk in men's minds? Yeah, the thing is that it may never enter "men's minds" -- an application would be written that grabs, say, 10 rows at random from the whole table, and ends up plugging in big numbers as in your example. Rarely do people think ahead to what happens when the tables get really big. Of course I don't imagine it'll be common either. :) Jon
Rod Taylor wrote: -- Start of PGP signed section. > On Wed, 2003-10-22 at 04:01, Christopher Kings-Lynne wrote: > > Hi guys, > > > > What is the limit on the number of rows in a PostgreSQL table? If it's > > more than MAXINT, we have a problem: > > > > phppgadmin# select * from test limit 2147483648; > > ERROR: integer out of range > > > > Same problem with OFFSET. > > I see you're point, but nobody is going to be interested in the first 2 > billion rows of a table without using a cursor and having some other > process do the math in the background. > > That said, perhaps the TODO for changing LIMIT / OFFSET to be expression > based should also mention bumping them to int8. Added to TODO: * Change LIMIT/OFFSET to use int8 -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073