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Bruce Momjian
26 years ago
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From owner-pgsql-hackers@hub.org Thu Sep 23 11:01:06 1999 |
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Thu, 23 Sep 1999 10:18:02 -0400 (EDT) |
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To: wieck@debis.com (Jan Wieck) |
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cc: pgsql-hackers@postgreSQL.org |
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Subject: Re: [HACKERS] Progress report: buffer refcount bugs and SQL functions |
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In-reply-to: Your message of Thu, 23 Sep 1999 03:19:39 +0200 (MET DST) |
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<m11TxXw-0003kLC@orion.SAPserv.Hamburg.dsh.de> |
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Date: Thu, 23 Sep 1999 10:18:01 -0400 |
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Message-ID: <13251.938096281@sss.pgh.pa.us> |
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From: Tom Lane <tgl@sss.pgh.pa.us> |
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Sender: owner-pgsql-hackers@postgreSQL.org |
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wieck@debis.com (Jan Wieck) writes: |
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> Tom Lane wrote: |
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>> What I am wondering, though, is whether this addition is actually |
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>> necessary, or is it a bug that the functions aren't run to completion |
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>> in the first place? |
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> I've said some time (maybe too long) ago, that SQL functions |
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> returning tuple sets are broken in general. |
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Indeed they are. Try this on for size (using the regression database): |
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SELECT p.name, p.hobbies.equipment.name FROM person p; |
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SELECT p.hobbies.equipment.name, p.name FROM person p; |
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You get different result sets!? |
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The problem in this example is that ExecTargetList returns the isDone |
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flag from the last targetlist entry, regardless of whether there are |
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incomplete iterations in previous entries. More generally, the buffer |
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leak problem that I started with only occurs if some Iter nodes are not |
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run to completion --- but execQual.c has no mechanism to make sure that |
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they have all reached completion simultaneously. |
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What we really need to make functions-returning-sets work properly is |
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an implementation somewhat like aggregate functions. We need to make |
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a list of all the Iter nodes present in a targetlist and cycle through |
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the values returned by each in a methodical fashion (run the rightmost |
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through its full cycle, then advance the next-to-rightmost one value, |
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run the rightmost through its cycle again, etc etc). Also there needs |
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to be an understanding of the hierarchy when an Iter appears in the |
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arguments of another Iter's function. (You cycle the upper one for |
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*each* set of arguments created by cycling its sub-Iters.) |
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I am not particularly interested in working on this feature right now, |
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since AFAIK it's a Berkeleyism not found in SQL92. What I've done |
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is to hack ExecTargetList so that it behaves semi-sanely when there's |
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more than one Iter at the top level of the target list --- it still |
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doesn't really give the right answer, but at least it will keep |
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generating tuples until all the Iters are done at the same time. |
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It happens that that's enough to give correct answers for the examples |
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shown in the misc regress test. Even when it fails to generate all |
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the possible combinations, there will be no buffer leaks. |
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So, I'm going to declare victory and go home ;-). We ought to add a |
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TODO item along the lines of |
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* Functions returning sets don't really work right |
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in hopes that someone will feel like tackling this someday. |
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regards, tom lane |
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************ |
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@ -0,0 +1,119 @@ |
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From owner-pgsql-general@hub.org Fri Oct 9 18:22:09 1998 |
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Date: Fri, 9 Oct 1998 18:18:00 -0400 (EDT) |
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From: Steve Doliov <statsol@statsol.com> |
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To: pgsql-general@postgreSQL.org |
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Subject: Re: [GENERAL] Making NULLs visible. |
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On Fri, 9 Oct 1998, Bruce Momjian wrote: |
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> [Charset iso-8859-1 unsupported, filtering to ASCII...] |
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> > > Yes, \ always outputs as \\, excepts someone changed it last week, and I |
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> > > am requesting a reversal. Do you like the \N if it is unique? |
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> > |
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> > Well, it's certainly clear, but could be confused with \n (newline). Can we |
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> > have \0 instead? |
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> |
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> Yes, but it is uppercase. \0 looks like an octal number to me, and I |
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> think we even output octals sometimes, don't we? |
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> |
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my first suggestion may have been hare-brained, but why not just make the |
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specifics of the output user-configurable. So if the user chooses \0, so |
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be it, if the user chooses \N so be it, if the user likes NULL so be it. |
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but the option would only have one value per database at any given point |
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in time. so database x could use \N on tuesday and NULL on wednesday, but |
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database x could never have two references to the characters(s) used to |
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represent a null value. |
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steve |
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From owner-pgsql-general@hub.org Sun Oct 11 17:31:08 1998 |
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Date: Sun, 11 Oct 1998 16:28:41 -0400 (EDT) |
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From: Thomas Good <tomg@admin.nrnet.org> |
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To: pgsql-general@postgreSQL.org |
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Subject: Re: [GENERAL] Making NULLs visible. |
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|
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Watching all this go by...as a guy who has to move alot of data |
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from legacy dbs to postgres, I've gotten used to \N being a null. |
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My vote, if I were allowed to cast one, would be to have one null |
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and that would be the COPY command null. I have no difficulty |
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distinguishing a null from a newline... |
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At the pgsql command prompt I would find seeing \N rather reassuring. |
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I've seen alot of these little guys. |
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---------- Sisters of Charity Medical Center ---------- |
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Department of Psychiatry |
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---- |
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Thomas Good <tomg@q8.nrnet.org> |
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Coordinator, North Richmond C.M.H.C. Information Systems |
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75 Vanderbilt Ave, Quarters 8 Phone: 718-354-5528 |
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Staten Island, NY 10304 Fax: 718-354-5056 |
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