Обсуждение: Table Partitioning is in 8.1
Table Partitioning is in 8.1 I've just read Peter Eisentraut's presentation to the Dutch gov (very good BTW). On the last page I read that Table Partitioning is a future for PostgreSQL....which is strange because Constraint Exclusion is an 8.1 feature. I've had five other people ask about it too in the last 2 weeks, and all have been surprised that this has now been accepted for 8.1 Is it possible that the Release Notes do not fully explain the Constraint Exclusion feature? Or is it the consensus that it works but not quite well enough to make a song and dance about yet? Certainly, my docs submission is overdue... Best Regards, Simon Riggs
On Wed, Sep 21, 2005 at 06:10:15PM +0100, Simon Riggs wrote: > Table Partitioning is in 8.1 > > I've just read Peter Eisentraut's presentation to the Dutch gov (very > good BTW). On the last page I read that Table Partitioning is a future > for PostgreSQL....which is strange because Constraint Exclusion is an > 8.1 feature. I think it depends on how closely you relate "Table Partitioning" and "Constraint Exclusion". While you can use the latter to implement the former, I think people expect a database that supports "Table Partitioning" to have a CREATE PARTITION command (or something similar). > Is it possible that the Release Notes do not fully explain the > Constraint Exclusion feature? Or is it the consensus that it works but > not quite well enough to make a song and dance about yet? IMHO, I think Constraint Exclusion is more useful in general and once it is in and tested future releases will have a partitioning system based upon it. Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
Simon Riggs <simon@2ndquadrant.com> writes:
> Is it possible that the Release Notes do not fully explain the
> Constraint Exclusion feature? Or is it the consensus that it works but
> not quite well enough to make a song and dance about yet?
I hardly think that the existing constraint-exclusion code is enough for
us to claim we "support table partitioning". There's too much grunt
work that the DBA still has to do to set up a partitioning arrangement.
regards, tom lane
On K, 2005-09-21 at 18:10 +0100, Simon Riggs wrote: > Table Partitioning is in 8.1 > > I've just read Peter Eisentraut's presentation to the Dutch gov (very > good BTW). On the last page I read that Table Partitioning is a future > for PostgreSQL....which is strange because Constraint Exclusion is an > 8.1 feature. > > I've had five other people ask about it too in the last 2 weeks, and all > have been surprised that this has now been accepted for 8.1 > > Is it possible that the Release Notes do not fully explain the > Constraint Exclusion feature? Or is it the consensus that it works but > not quite well enough to make a song and dance about yet? It sure makes implementing Table Partitioning using inheritance much simpler and efficient, and should be documented as such. The release notes should certainly mention the words "Table Partitioning" together with Constraint Exclusion so that people looking (grepping) for partitioning will find it. > Certainly, my docs submission is overdue... This could be one of the reasons CE is not recognised as a feature supporting table partitioning. ;) -- Hannu Krosing <hannu@skype.net>
On K, 2005-09-21 at 15:39 -0400, Tom Lane wrote: > Simon Riggs <simon@2ndquadrant.com> writes: > > Is it possible that the Release Notes do not fully explain the > > Constraint Exclusion feature? Or is it the consensus that it works but > > not quite well enough to make a song and dance about yet? > > I hardly think that the existing constraint-exclusion code is enough for > us to claim we "support table partitioning". There's too much grunt > work that the DBA still has to do to set up a partitioning arrangement. We can probably claim that : "Postgres has *low-level* support for table partitioning using and Inheritance, Rules/Triggers and Constraint Exclusion , enabling DBAs to set up complex partitioning schemes" There certainly is much grunt work, but then we can get a better CE performance than just "PARTITION TABLE TTT BY XXX" would give by having constraints on multiple fields in some/all partitions, both overlapping and not, possibly resulting in a better overall system. That is what "low-level" in the above statement means. -- Hannu Krosing <hannu@skype.net>
On Wed, 2005-09-21 at 15:39 -0400, Tom Lane wrote: > Simon Riggs <simon@2ndquadrant.com> writes: > > Is it possible that the Release Notes do not fully explain the > > Constraint Exclusion feature? Or is it the consensus that it works but > > not quite well enough to make a song and dance about yet? > > I hardly think that the existing constraint-exclusion code is enough for > us to claim we "support table partitioning". There's too much grunt > work that the DBA still has to do to set up a partitioning arrangement. So you think the DBA can do partitioning? Good. Setting up partitioning in Oracle or SQLServer2005 requires lots of syntax and multiple commands. There are fewer commands with PostgreSQL and they are ISO/ANSI compliant also. I think there is much still left to do with partitioning, so I would be the first to say that this is only the beginning. I know you are wary of overstating capabilities; so am I, but it looks like we differ slightly on where to draw the line. On reflection, the only changes I suggest are: 1) the phrase "This allows for a type of table partitioning" have the word "basic" inserted within it to become: "This allows for a basic type of table partitioning" 2) placing CE as a major feature of 8.1 - many people regard it at least as highly as other optimizations, though this is subjective based upon their application requirements Suggestion (2) might be seen as some kind of vanity, so having raised the issue I'll leave the floor open to others to agree or not. Best Regards, Simon Riggs
On Thu, Sep 22, 2005 at 10:11:50AM +0100, Simon Riggs wrote: > On Wed, 2005-09-21 at 15:39 -0400, Tom Lane wrote: > > Simon Riggs <simon@2ndquadrant.com> writes: > > > Is it possible that the Release Notes do not fully explain the > > > Constraint Exclusion feature? Or is it the consensus that it works but > > > not quite well enough to make a song and dance about yet? > > > > I hardly think that the existing constraint-exclusion code is enough for > > us to claim we "support table partitioning". There's too much grunt > > work that the DBA still has to do to set up a partitioning arrangement. > > So you think the DBA can do partitioning? Good. > > Setting up partitioning in Oracle or SQLServer2005 requires lots of > syntax and multiple commands. There are fewer commands with PostgreSQL > and they are ISO/ANSI compliant also. Actually, IIRC it takes 2 commands; one to initially setup the partitioning and one to create new partitions as needed. 3 commands if you count DROP PARTITON. It's been a while since I looked at what you've done, but I seem to recall needing to manually maintain rules every time you create a new partition. -- Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
> > On reflection, the only changes I suggest are: > > 1) the phrase "This allows for a type of table partitioning" have the > word "basic" inserted within it to become: "This allows for a basic type > of table partitioning" How about just: Initial support for table partitioning. Yes it is non-committal but that is a good thing since nobody 100% agrees anyway. Sincerely, Joshua D. Drake > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: Have you checked our extensive FAQ? > > http://www.postgresql.org/docs/faq -- Your PostgreSQL solutions company - Command Prompt, Inc. 1.800.492.2240 PostgreSQL Replication, Consulting, Custom Programming, 24x7 support Managed Services, Shared and Dedicated Hosting Co-Authors: plPHP, plPerlNG - http://www.commandprompt.com/
Word "basic" added. --------------------------------------------------------------------------- Joshua D. Drake wrote: > > > > On reflection, the only changes I suggest are: > > > > 1) the phrase "This allows for a type of table partitioning" have the > > word "basic" inserted within it to become: "This allows for a basic type > > of table partitioning" > > How about just: Initial support for table partitioning. Yes it is > non-committal but that is a good thing since nobody 100% agrees anyway. > > Sincerely, > > Joshua D. Drake > > > > > > > ---------------------------(end of broadcast)--------------------------- > > TIP 3: Have you checked our extensive FAQ? > > > > http://www.postgresql.org/docs/faq > > > -- > Your PostgreSQL solutions company - Command Prompt, Inc. 1.800.492.2240 > PostgreSQL Replication, Consulting, Custom Programming, 24x7 support > Managed Services, Shared and Dedicated Hosting > Co-Authors: plPHP, plPerlNG - http://www.commandprompt.com/ > > ---------------------------(end of broadcast)--------------------------- > TIP 5: don't forget to increase your free space map settings > -- 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
Simon Riggs wrote:
> On Wed, 2005-09-21 at 15:39 -0400, Tom Lane wrote:
> > Simon Riggs <simon@2ndquadrant.com> writes:
> > > Is it possible that the Release Notes do not fully explain the
> > > Constraint Exclusion feature? Or is it the consensus that it works but
> > > not quite well enough to make a song and dance about yet?
> >
> > I hardly think that the existing constraint-exclusion code is enough for
> > us to claim we "support table partitioning". There's too much grunt
> > work that the DBA still has to do to set up a partitioning arrangement.
>
> So you think the DBA can do partitioning? Good.
>
> Setting up partitioning in Oracle or SQLServer2005 requires lots of
> syntax and multiple commands. There are fewer commands with PostgreSQL
> and they are ISO/ANSI compliant also.
>
> I think there is much still left to do with partitioning, so I would be
> the first to say that this is only the beginning. I know you are wary of
> overstating capabilities; so am I, but it looks like we differ slightly
> on where to draw the line.
>
> On reflection, the only changes I suggest are:
>
> 1) the phrase "This allows for a type of table partitioning" have the
> word "basic" inserted within it to become: "This allows for a basic type
> of table partitioning"
>
> 2) placing CE as a major feature of 8.1 - many people regard it at least
> as highly as other optimizations, though this is subjective based upon
> their application requirements
>
> Suggestion (2) might be seen as some kind of vanity, so having raised
> the issue I'll leave the floor open to others to agree or not.
Having heard no comments, I have moved this item up into the main
features section of the release notes, and reworded it:
Improve performance for partitioned tables (Simon)
The new constraint_exclusion configuration parameter avoids lookups on child tables where constraints
indicate that no matching rows exist in the child table.
This allows for a basic type of table partitioning. If child tables store separate key ranges and this
is enforced using appropriate "CHECK" constraints, the optimizer will skip child table accesses when the
constraint guarantees no matching rows exist in the child table.
-- 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
On Thu, 2005-09-22 at 14:37 -0500, Jim C. Nasby wrote: > On Thu, Sep 22, 2005 at 10:11:50AM +0100, Simon Riggs wrote: > > On Wed, 2005-09-21 at 15:39 -0400, Tom Lane wrote: > > > Simon Riggs <simon@2ndquadrant.com> writes: > > > > Is it possible that the Release Notes do not fully explain the > > > > Constraint Exclusion feature? Or is it the consensus that it works but > > > > not quite well enough to make a song and dance about yet? > > > > > > I hardly think that the existing constraint-exclusion code is enough for > > > us to claim we "support table partitioning". There's too much grunt > > > work that the DBA still has to do to set up a partitioning arrangement. > > > > So you think the DBA can do partitioning? Good. > > > > Setting up partitioning in Oracle or SQLServer2005 requires lots of > > syntax and multiple commands. There are fewer commands with PostgreSQL > > and they are ISO/ANSI compliant also. > > Actually, IIRC it takes 2 commands; one to initially setup the > partitioning and one to create new partitions as needed. 3 commands if > you count DROP PARTITON. Which is what it takes in PostgreSQL. > It's been a while since I looked at what you've done, but I seem to > recall needing to manually maintain rules every time you create a new > partition. All current implementations I am aware of require Declarative statements each time a new partition is started. But there is no *need* to create RULEs. You would need to do that if you wanted automatic routing of INSERT statements. The current PostgreSQL implementation does not do this, and yes, this would require creating a set of Rule statements to do this - though possible to do this automatically with a simple script. My experience with Oracle has been that one loads into specifically identified partitions, so the loading case for PostgreSQL is essentially identical to the common case for Oracle. My experience may not be everybody's, so I may be off-base on this, but I've not put a priority on solving that issue. Do people consider that aspect essential to the wider use of partitioning? I don't consider CE to be complete, any more than any newly introduced major feature set, but IMHO the important first order functionality is now available in PostgreSQL. I'm looking at probably Tuesday to submit first draft docs. Best Regards, Simon Riggs
Hi, I seem to recall that in Oracle you load into specific partitions without specifically naming them in insert statements (in other words you insert into table, the engine redirects data to the corrisponding partition), I quickly looked at postgresql partitioning and it seems to me that you need to insert into a specified derived table (unless you set up rules). It would be good to have an insert behaviour similar to Oracle by default. Also I see that the original table is always scanned, partition exclusion happens only on the derived tables, is this correct? Regards paolo > -----Messaggio originale----- > Da: pgsql-hackers-owner@postgresql.org > [mailto:pgsql-hackers-owner@postgresql.org]Per conto di Simon Riggs > Inviato: venerdì 23 settembre 2005 11.51 > A: Jim C. Nasby > Cc: Tom Lane; pgsql-hackers@postgresql.org > Oggetto: Re: [HACKERS] Table Partitioning is in 8.1 > > > On Thu, 2005-09-22 at 14:37 -0500, Jim C. Nasby wrote: > > On Thu, Sep 22, 2005 at 10:11:50AM +0100, Simon Riggs wrote: > > > On Wed, 2005-09-21 at 15:39 -0400, Tom Lane wrote: > > > > Simon Riggs <simon@2ndquadrant.com> writes: > > > > > Is it possible that the Release Notes do not fully explain the > > > > > Constraint Exclusion feature? Or is it the consensus that > it works but > > > > > not quite well enough to make a song and dance about yet? > > > > > > > > I hardly think that the existing constraint-exclusion code > is enough for > > > > us to claim we "support table partitioning". There's too much grunt > > > > work that the DBA still has to do to set up a partitioning > arrangement. > > > > > > So you think the DBA can do partitioning? Good. > > > > > > Setting up partitioning in Oracle or SQLServer2005 requires lots of > > > syntax and multiple commands. There are fewer commands with PostgreSQL > > > and they are ISO/ANSI compliant also. > > > > Actually, IIRC it takes 2 commands; one to initially setup the > > partitioning and one to create new partitions as needed. 3 commands if > > you count DROP PARTITON. > > Which is what it takes in PostgreSQL. > > > It's been a while since I looked at what you've done, but I seem to > > recall needing to manually maintain rules every time you create a new > > partition. > > All current implementations I am aware of require Declarative statements > each time a new partition is started. > > But there is no *need* to create RULEs. You would need to do that if you > wanted automatic routing of INSERT statements. The current PostgreSQL > implementation does not do this, and yes, this would require creating a > set of Rule statements to do this - though possible to do this > automatically with a simple script. My experience with Oracle has been > that one loads into specifically identified partitions, so the loading > case for PostgreSQL is essentially identical to the common case for > Oracle. My experience may not be everybody's, so I may be off-base on > this, but I've not put a priority on solving that issue. Do people > consider that aspect essential to the wider use of partitioning? > > I don't consider CE to be complete, any more than any newly introduced > major feature set, but IMHO the important first order functionality is > now available in PostgreSQL. > > I'm looking at probably Tuesday to submit first draft docs. > > Best Regards, Simon Riggs > > > > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly >
On Fri, 2005-09-23 at 12:30 +0200, Paolo Magnoli wrote: > It would be good to have an insert behaviour similar to Oracle by default. OK, thanks. > Also I see that the original table is always scanned, partition exclusion > happens only on the derived tables, is this correct? Yes, though if you avoid placing any rows in that table it is quick. I expect to remove that restriction in 8.2 by declarative SQL. Best Regards, Simon Riggs
Paolo Magnoli wrote: > Hi, I seem to recall that in Oracle you load into specific partitions > without specifically naming them in insert statements (in other words you > insert into table, the engine redirects data to the corrisponding > partition), This is correct -- _______________________________ This e-mail may be privileged and/or confidential, and the sender does not waive any related rights and obligations. Any distribution, use or copying of this e-mail or the information it contains by other than an intended recipient is unauthorized. If you received this e-mail in error, please advise me (by return e-mail or otherwise) immediately. _______________________________