Обсуждение: help bug and comment char.
Hi all In looking for how to do table constraints psql help says: software=> \h create table Command: create table Description: create a new table Syntax: CREATE TABLE class_name (attr1 type1 [DEFAULT expression] [NOT NULL], ...attrN) [INHERITS (class_name1,...class_nameN) [[CONSTRAINT name] CHECK condition1, ...conditionN] ] ; But this both does not work, and does not agree with "The Practical SQL Handbook", the examples of which do work. Should the syntax not be more like: (constraint inside the main parens) Command: create table Description: create a new table Syntax: CREATE TABLE class_name (attr1 type1 [DEFAULT expression] [NOT NULL][, ...attrN] [,[CONSTRAINTname] CHECK condition1, ...conditionN] ]); I'm not sure where to put: [INHERITS (class_name1, ...class_nameN) as I've never used it. But I suspect it may need inside the '()' as well, no? OH, also, what is / is there, a comment character to use in SQL scripts feed into psql? Have a great day Terry Mackintosh <terry@terrym.com> http://www.terrym.com sysadmin/owner I'm excited about life! How about YOU!? Proudly powered by R H Linux 4.2, Apache 1.3.x, PHP 3.x, PostgreSQL 6.x ----------------------------------------------------------------------- Only if you know where you're going can you get there.
> In looking for how to do table constraints psql help says:
> software=> \h create table
> Command: create table
> Description: create a new table
> Syntax:
> CREATE TABLE class_name
> (attr1 type1 [DEFAULT expression] [NOT NULL], ...attrN)
> [INHERITS (class_name1, ...class_nameN)
> [[CONSTRAINT name] CHECK condition1, ...conditionN]]
This syntax help is out of date. The syntax for v6.4 (and perhaps
v6.3.2) became compatible with SQL92, except of course for the INHERITS
clause. That still must appear outside of the column-definition parens.
- Tom
> Hi all
>
> In looking for how to do table constraints psql help says:
>
> software=> \h create table
> Command: create table
> Description: create a new table
> Syntax:
> CREATE TABLE class_name
> (attr1 type1 [DEFAULT expression] [NOT NULL], ...attrN)
> [INHERITS (class_name1, ...class_nameN)
> [[CONSTRAINT name] CHECK condition1, ...conditionN] ]
> ;
>
>
> But this both does not work, and does not agree with "The Practical SQL
> Handbook", the examples of which do work.
>
> Should the syntax not be more like: (constraint inside the main parens)
>
> Command: create table
> Description: create a new table
> Syntax:
> CREATE TABLE class_name
> (attr1 type1 [DEFAULT expression] [NOT NULL][, ...attrN]
> [,[CONSTRAINT name] CHECK condition1, ...conditionN] ]);
Fixed.
>
> I'm not sure where to put:
> [INHERITS (class_name1, ...class_nameN)
> as I've never used it. But I suspect it may need inside the '()' as well,
> no?
>
> OH, also, what is / is there, a comment character to use in SQL scripts
> feed into psql?
-- is the comment character. Man sql says:
---------------------------------------------------------------------------
Comments A comment is an arbitrary sequence of characters following double dashes up to the end of the line.
Wealso support double-slashes as comments, e.g.: -- This is a standard SQL comment // And this is
anothersupported comment style, like C++
We also support C-style comments, e.g.: /* multi line comment */
-- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
> > In looking for how to do table constraints psql help says: > > software=> \h create table > > Command: create table > > Description: create a new table > > Syntax: > > CREATE TABLE class_name > > (attr1 type1 [DEFAULT expression] [NOT NULL], ...attrN) > > [INHERITS (class_name1, ...class_nameN) > > [[CONSTRAINT name] CHECK condition1, ...conditionN]] > > This syntax help is out of date. The syntax for v6.4 (and perhaps > v6.3.2) became compatible with SQL92, except of course for the INHERITS > clause. That still must appear outside of the column-definition parens. Fixed. -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Hi PostgreSQL hackers As we are again approaching the beta (feature freeze), I will ask my ordinary question ;) Is the patch by Jan that eliminated the duplicate sort node in case it was redundant included in 6.5 ? --------------- Hannu
>
> Hi PostgreSQL hackers
>
> As we are again approaching the beta (feature freeze),
> I will ask my ordinary question ;)
>
> Is the patch by Jan that eliminated the duplicate sort node in case it
> was redundant included in 6.5 ?
Sorry,
I missed to put it into after v6.4 release. And since it
wasn't there during v6.5 development, I would not put it in
now.
Note that it wasn't in the v6.4 feature patches either, so it
isn't tested enough to get released.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
> > > > Hi PostgreSQL hackers > > > > As we are again approaching the beta (feature freeze), > > I will ask my ordinary question ;) > > > > Is the patch by Jan that eliminated the duplicate sort node in case it > > was redundant included in 6.5 ? > > Sorry, > > I missed to put it into after v6.4 release. And since it > wasn't there during v6.5 development, I would not put it in > now. > > Note that it wasn't in the v6.4 feature patches either, so it > isn't tested enough to get released. We haven't started beta yet. Anything on LIMIT? -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
>
> > >
> > > Hi PostgreSQL hackers
> > >
> > > As we are again approaching the beta (feature freeze),
> > > I will ask my ordinary question ;)
> > >
> > > Is the patch by Jan that eliminated the duplicate sort node in case it
> > > was redundant included in 6.5 ?
> >
> > Sorry,
> >
> > I missed to put it into after v6.4 release. And since it
> > wasn't there during v6.5 development, I would not put it in
> > now.
> >
> > Note that it wasn't in the v6.4 feature patches either, so it
> > isn't tested enough to get released.
>
> We haven't started beta yet. Anything on LIMIT?
LIMIT is in there and was during entire v6.5 development.
But ORDER BY suppressing sort using index wasn't.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
> > We haven't started beta yet. Anything on LIMIT? > > LIMIT is in there and was during entire v6.5 development. > But ORDER BY suppressing sort using index wasn't. > Great. -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
Jan Wieck wrote: > > > > > Hi PostgreSQL hackers > > > > As we are again approaching the beta (feature freeze), > > I will ask my ordinary question ;) > > > > Is the patch by Jan that eliminated the duplicate sort node in case it > > was redundant included in 6.5 ? > > Sorry, > > I missed to put it into after v6.4 release. And since it > wasn't there during v6.5 development, I would not put it in > now. > > Note that it wasn't in the v6.4 feature patches either, so it > isn't tested enough to get released. But if it is not relesed it will _never_ be tested enough ... As we are just going into beta, not relese, I would suggest to put it in now, and back out if it relly breaks anything. I have been using it with 6.4 almost since the relese an have seen no problems - in fact it solved a big problem and provided about 1000X speedup for certain queries (a fraction of second instead of 6 minutes) , not to mention avoiding backend crashes due to disk space exhaustion. And it did not break anything in regression tests either, the only argument then was that there is nothing in regression tests that could possibly be broken by it ;) I greatly prefer it over my previous method of doing the same on the client side (issuing an EXPLAIN, parsing it to see if it is SORT on INDEX SCAN, and omitting the ORDER BY if it is) Also, not having it greatly diminishes the value of LIMIT. I agree that it is a hack and only a partial solution and that in ideal world the optimiser would also know about sort nodes. But it is a very useful hack, and for some (like me) it is much bigger improvement than some 10% due to better memory allocation (which is of course great too). ---------------- Hannu
Hannu Krosing wrote: > > Jan Wieck wrote: > > > > > > Is the patch by Jan that eliminated the duplicate sort node in case it > > > was redundant included in 6.5 ? > > > > Sorry, > > > > I missed to put it into after v6.4 release. And since it > > wasn't there during v6.5 development, I would not put it in ... > But if it is not relesed it will _never_ be tested enough ... > > As we are just going into beta, not relese, I would suggest to put > it in now, and back out if it relly breaks anything. I will download the latest snapshot tonight and test the patch there. Does anyone know if something introduced in 6.5 can break by omitting the top sort node ? Perhaps any of the following: * MVCC * temp tables * Some exotic use of rules * SELECT FOR UPDATE I myself can't see how it could break, as the only thing the patch does is omitting a top sort node if the query is already in the right order. So it should be equivalent of just not including the ORDER BY in the SELECT in the first place. Jan - I often feel the same about some of my code that are part of some larger complex project (ie. if it aint broke, don't fix it), but this time I think the patch is quite safe, and very very useful for at least two occasions: getting the start of some table out to users web and for processing huge tables in predictable/repeatable order. I somewhat understand your hesitation, because I can't either think of any test in regression that could be broken by the patch, but instead of making me uneasy it makes me happy ;) ----------------- Hannu
Hannu Krosing wrote:
>
> Jan Wieck wrote:
> >
> > >
> > > Hi PostgreSQL hackers
> > >
> > > As we are again approaching the beta (feature freeze),
> > > I will ask my ordinary question ;)
> > >
> > > Is the patch by Jan that eliminated the duplicate sort node in case it
> > > was redundant included in 6.5 ?
> >
> > Sorry,
> >
> > I missed to put it into after v6.4 release. And since it
> > wasn't there during v6.5 development, I would not put it in
> > now.
> >
> > Note that it wasn't in the v6.4 feature patches either, so it
> > isn't tested enough to get released.
>
> But if it is not relesed it will _never_ be tested enough ...
>
> As we are just going into beta, not relese, I would suggest to put
> it in now, and back out if it relly breaks anything.
>
> I have been using it with 6.4 almost since the relese an have
> seen no problems - in fact it solved a big problem and provided about
> 1000X speedup for certain queries (a fraction of second instead of
> 6 minutes) , not to mention avoiding backend crashes due to disk space
> exhaustion.
>
> And it did not break anything in regression tests either, the only
> argument then was that there is nothing in regression tests that
> could possibly be broken by it ;)
>
> I greatly prefer it over my previous method of doing the same on the
> client side (issuing an EXPLAIN, parsing it to see if it is SORT on
> INDEX SCAN, and omitting the ORDER BY if it is)
>
> Also, not having it greatly diminishes the value of LIMIT.
Ok ok ok - OK. You got me, I'll go ahead and put it in.
>
> I agree that it is a hack and only a partial solution and that in
> ideal world the optimiser would also know about sort nodes.
First the executor must know better how to handle LIMIT's
OFFSET. For now it processes the query until OFFSET is
reached, simply suppressing the in fact produced result
tuples in the output. The it stops sending if the LIMIT count
is reached. For joins or other complex things, it has no
chance to do something different. But for an indexed single
table scan, where ALL the qualifications are done on the
index, it should handle the OFFSET by skipping index tuples
only.
Second the optimizer must take LIMIT into account and
depending on the known number of tuples, LIMIT and OFFSET
produce an index scan even if the query isn't qualified at
all but has an ORDER BY clause matched by the index.
These two features would finally solve your huge table
problems.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
On Wed, 3 Feb 1999, Jan Wieck wrote:
> >
> > > >
> > > > Hi PostgreSQL hackers
> > > >
> > > > As we are again approaching the beta (feature freeze),
> > > > I will ask my ordinary question ;)
> > > >
> > > > Is the patch by Jan that eliminated the duplicate sort node in case it
> > > > was redundant included in 6.5 ?
> > >
> > > Sorry,
> > >
> > > I missed to put it into after v6.4 release. And since it
> > > wasn't there during v6.5 development, I would not put it in
> > > now.
> > >
> > > Note that it wasn't in the v6.4 feature patches either, so it
> > > isn't tested enough to get released.
> >
> > We haven't started beta yet. Anything on LIMIT?
>
> LIMIT is in there and was during entire v6.5 development.
> But ORDER BY suppressing sort using index wasn't.
Sinc we haven't started BETA yet, why not throw it in? Once beta, we stil
lhave another month of testing before release, so lots of time...
Marc G. Fournier
Systems Administrator @ hub.org
primary: scrappy@hub.org secondary: scrappy@{freebsd|postgresql}.org
Jan Wieck wrote: > > > Ok ok ok - OK. You got me, I'll go ahead and put it in. Thanks ;) > > I agree that it is a hack and only a partial solution and that in > > ideal world the optimiser would also know about sort nodes. > > First the executor must know better how to handle LIMIT's > OFFSET. For now it processes the query until OFFSET is > reached, simply suppressing the in fact produced result > tuples in the output. The it stops sending if the LIMIT count > is reached. For joins or other complex things, it has no > chance to do something different. But for an indexed single > table scan, where ALL the qualifications are done on the > index, it should handle the OFFSET by skipping index tuples > only. And we must also tie this kind of scan to triggers (my quess is that currently the triggers are fired by accessing the data in the actual relation data). It probably does not affect rules as much, though it would be cool to define rules for index scans or sort nodes. > Second the optimizer must take LIMIT into account and > depending on the known number of tuples, LIMIT and OFFSET > produce an index scan even if the query isn't qualified at > all but has an ORDER BY clause matched by the index. > > These two features would finally solve your huge table > problems. Yes, it seems so. Next thing to attack then would be aggregates, so that they too can benefit from indexes, I can immediately think of MIN, MAX and COUNT on simple scans. But as the aggregates are user-defined, we probably need a flag that tells the optimiser if said aggregate can in fact use indexes (and what type of index) Maybe we can even cache some data (for example tuple count) in backend, so that COUNT(*) can be made real fast ? After that the reverse index scans, so that the index that are backwards can also be used for sorting. BTW, can this be easily implemented/effective in PostgreSQL or are our btree indexes optimised for forward scans ? Also, how do indexes interact with TRX manager (is there some docs on it). --------------------- Hannu
> Next thing to attack then would be aggregates, so that they too can > benefit from indexes, I can immediately think of MIN, MAX and COUNT > on simple scans. But as the aggregates are user-defined, we probably > need a flag that tells the optimiser if said aggregate can in fact > use indexes (and what type of index) > > Maybe we can even cache some data (for example tuple count) in > backend, so that COUNT(*) can be made real fast ? > > After that the reverse index scans, so that the index that are > backwards can also be used for sorting. > BTW, can this be easily implemented/effective in PostgreSQL or are > our btree indexes optimised for forward scans ? Jan, I have kept the postings on optimizing LIMIT for joins. Let me know if/when you want to see them. -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
> Jan, I have kept the postings on optimizing LIMIT for joins. Let me
> know if/when you want to see them.
Are they patches ready to go in or just suggestions how to
do?
ORDER BY patch is now in CURRENT.
Jan
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
Hello all, > -----Original Message----- > From: owner-pgsql-hackers@postgreSQL.org > [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Hannu Krosing > Sent: Thursday, February 04, 1999 3:43 AM > To: Jan Wieck > Cc: hackers@postgreSQL.org > Subject: Re: [HACKERS] 6.5 beta and ORDER BY patch > [snip] > > After that the reverse index scans, so that the index that are > backwards can also be used for sorting. > BTW, can this be easily implemented/effective in PostgreSQL or are > our btree indexes optimised for forward scans ? > PostgreSQL seems to have the ability to scan Index backward because we can execute "fetch backward" command. IMHO _bt_first() fucntion used to find first item in a scan should be changed to work well in case of backward positioning. I think this change also gives the partial solution for the problem [ [HACKERS] Cursor Movement - Past the End ] reported by David Hartwig. I have a sample code for this change. I can send it if someone want to check or test it. Thanks. Hiroshi Inoue Inoue@tpf.co.jp
Jan, is this implemented in 6.5 beta? > > > > As we are again approaching the beta (feature freeze), > > > > I will ask my ordinary question ;) > > > > > > > > Is the patch by Jan that eliminated the duplicate sort node in case it > > > > was redundant included in 6.5 ? > > > > > > Sorry, > > > > > > I missed to put it into after v6.4 release. And since it > > > wasn't there during v6.5 development, I would not put it in > > > now. > > > > > > Note that it wasn't in the v6.4 feature patches either, so it > > > isn't tested enough to get released. > > > > But if it is not relesed it will _never_ be tested enough ... > > > > As we are just going into beta, not relese, I would suggest to put > > it in now, and back out if it relly breaks anything. > > > > I have been using it with 6.4 almost since the relese an have > > seen no problems - in fact it solved a big problem and provided about > > 1000X speedup for certain queries (a fraction of second instead of > > 6 minutes) , not to mention avoiding backend crashes due to disk space > > exhaustion. > > > > And it did not break anything in regression tests either, the only > > argument then was that there is nothing in regression tests that > > could possibly be broken by it ;) > > > > I greatly prefer it over my previous method of doing the same on the > > client side (issuing an EXPLAIN, parsing it to see if it is SORT on > > INDEX SCAN, and omitting the ORDER BY if it is) > > > > Also, not having it greatly diminishes the value of LIMIT. > > Ok ok ok - OK. You got me, I'll go ahead and put it in. > > > > > I agree that it is a hack and only a partial solution and that in > > ideal world the optimiser would also know about sort nodes. > > First the executor must know better how to handle LIMIT's > OFFSET. For now it processes the query until OFFSET is > reached, simply suppressing the in fact produced result > tuples in the output. The it stops sending if the LIMIT count > is reached. For joins or other complex things, it has no > chance to do something different. But for an indexed single > table scan, where ALL the qualifications are done on the > index, it should handle the OFFSET by skipping index tuples > only. > > Second the optimizer must take LIMIT into account and > depending on the known number of tuples, LIMIT and OFFSET > produce an index scan even if the query isn't qualified at > all but has an ORDER BY clause matched by the index. > > These two features would finally solve your huge table > problems. > -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
It is my assumption this has been applied to 6.5 beta, right? [Charset iso-8859-1 unsupported, filtering to ASCII...] > Hello all, > > > -----Original Message----- > > From: owner-pgsql-hackers@postgreSQL.org > > [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Hannu Krosing > > Sent: Thursday, February 04, 1999 3:43 AM > > To: Jan Wieck > > Cc: hackers@postgreSQL.org > > Subject: Re: [HACKERS] 6.5 beta and ORDER BY patch > > > > [snip] > > > > > After that the reverse index scans, so that the index that are > > backwards can also be used for sorting. > > BTW, can this be easily implemented/effective in PostgreSQL or are > > our btree indexes optimised for forward scans ? > > > > PostgreSQL seems to have the ability to scan Index backward > because we can execute "fetch backward" command. > IMHO _bt_first() fucntion used to find first item in a scan should > be changed to work well in case of backward positioning. > > I think this change also gives the partial solution for the problem > [ [HACKERS] Cursor Movement - Past the End ] reported by > David Hartwig. > > I have a sample code for this change. > I can send it if someone want to check or test it. > > Thanks. > > Hiroshi Inoue > Inoue@tpf.co.jp > > -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026
> -----Original Message----- > From: Bruce Momjian [mailto:maillist@candle.pha.pa.us] > Sent: Sunday, May 09, 1999 8:56 PM > To: Hiroshi Inoue > Cc: Hannu Krosing; David Hartwig; Jan Wieck; pgsql-hackers > Subject: Re: [HACKERS] 6.5 beta and ORDER BY patch > > > It is my assumption this has been applied to 6.5 beta, right? > It has been applied with subject [Index backward scan patch]. However it doesn't include a change to omit sorting in all descending ORDER BY cases. Thanks. Hiroshi Inoue Inoue@tpf.co.jp > [Charset iso-8859-1 unsupported, filtering to ASCII...] > > Hello all, > > > > > -----Original Message----- > > > From: owner-pgsql-hackers@postgreSQL.org > > > [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Hannu Krosing > > > Sent: Thursday, February 04, 1999 3:43 AM > > > To: Jan Wieck > > > Cc: hackers@postgreSQL.org > > > Subject: Re: [HACKERS] 6.5 beta and ORDER BY patch > > > > > > > [snip] > > > > > > > > After that the reverse index scans, so that the index that are > > > backwards can also be used for sorting. > > > BTW, can this be easily implemented/effective in PostgreSQL or are > > > our btree indexes optimised for forward scans ? > > > > > > > PostgreSQL seems to have the ability to scan Index backward > > because we can execute "fetch backward" command. > > IMHO _bt_first() fucntion used to find first item in a scan should > > be changed to work well in case of backward positioning. > > > > I think this change also gives the partial solution for the problem > > [ [HACKERS] Cursor Movement - Past the End ] reported by > > David Hartwig. > > > > I have a sample code for this change. > > I can send it if someone want to check or test it. > > > > Thanks. > > > > Hiroshi Inoue > > Inoue@tpf.co.jp > > > > > > > -- > Bruce Momjian | http://www.op.net/~candle > maillist@candle.pha.pa.us | (610) 853-3000 > + If your life is a hard drive, | 830 Blythe Avenue > + Christ can be your backup. | Drexel Hill, Pennsylvania 19026 >
>
>
> Jan, is this implemented in 6.5 beta?
It is still the simple suppressing of the sort if the choosen
index scan has already the requested sort order. The possible
enhancements of the optimizer (mainly taking LIMIT into
account and use index scan if sort order can be obtained from
that) aren't implemented AFAIK.
I have too less knowledge in the planner/optimizer corner to
get my hands on it at this stage! And there are things left
in the rewrite system. It might be better to leave this all
for v6.6.
Jan
>
> > > > > As we are again approaching the beta (feature freeze),
> > > > > I will ask my ordinary question ;)
> > > > >
> > > > > Is the patch by Jan that eliminated the duplicate sort node in case it
> > > > > was redundant included in 6.5 ?
> > > >
> > > > Sorry,
> > > >
> > > > I missed to put it into after v6.4 release. And since it
> > > > wasn't there during v6.5 development, I would not put it in
> > > > now.
> > > >
> > > > Note that it wasn't in the v6.4 feature patches either, so it
> > > > isn't tested enough to get released.
> > >
> > > But if it is not relesed it will _never_ be tested enough ...
> > >
> > > As we are just going into beta, not relese, I would suggest to put
> > > it in now, and back out if it relly breaks anything.
> > >
> > > I have been using it with 6.4 almost since the relese an have
> > > seen no problems - in fact it solved a big problem and provided about
> > > 1000X speedup for certain queries (a fraction of second instead of
> > > 6 minutes) , not to mention avoiding backend crashes due to disk space
> > > exhaustion.
> > >
> > > And it did not break anything in regression tests either, the only
> > > argument then was that there is nothing in regression tests that
> > > could possibly be broken by it ;)
> > >
> > > I greatly prefer it over my previous method of doing the same on the
> > > client side (issuing an EXPLAIN, parsing it to see if it is SORT on
> > > INDEX SCAN, and omitting the ORDER BY if it is)
> > >
> > > Also, not having it greatly diminishes the value of LIMIT.
> >
> > Ok ok ok - OK. You got me, I'll go ahead and put it in.
> >
> > >
> > > I agree that it is a hack and only a partial solution and that in
> > > ideal world the optimiser would also know about sort nodes.
> >
> > First the executor must know better how to handle LIMIT's
> > OFFSET. For now it processes the query until OFFSET is
> > reached, simply suppressing the in fact produced result
> > tuples in the output. The it stops sending if the LIMIT count
> > is reached. For joins or other complex things, it has no
> > chance to do something different. But for an indexed single
> > table scan, where ALL the qualifications are done on the
> > index, it should handle the OFFSET by skipping index tuples
> > only.
> >
> > Second the optimizer must take LIMIT into account and
> > depending on the known number of tuples, LIMIT and OFFSET
> > produce an index scan even if the query isn't qualified at
> > all but has an ORDER BY clause matched by the index.
> >
> > These two features would finally solve your huge table
> > problems.
> >
>
>
> --
> Bruce Momjian | http://www.op.net/~candle
> maillist@candle.pha.pa.us | (610) 853-3000
> + If your life is a hard drive, | 830 Blythe Avenue
> + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
>
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
>
> It is my assumption this has been applied to 6.5 beta, right?
Don't know. Hiroshi - do you see your code anywhere?
Jan
>
> [Charset iso-8859-1 unsupported, filtering to ASCII...]
> > Hello all,
> >
> > > -----Original Message-----
> > > From: owner-pgsql-hackers@postgreSQL.org
> > > [mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Hannu Krosing
> > > Sent: Thursday, February 04, 1999 3:43 AM
> > > To: Jan Wieck
> > > Cc: hackers@postgreSQL.org
> > > Subject: Re: [HACKERS] 6.5 beta and ORDER BY patch
> > >
> >
> > [snip]
> >
> > >
> > > After that the reverse index scans, so that the index that are
> > > backwards can also be used for sorting.
> > > BTW, can this be easily implemented/effective in PostgreSQL or are
> > > our btree indexes optimised for forward scans ?
> > >
> >
> > PostgreSQL seems to have the ability to scan Index backward
> > because we can execute "fetch backward" command.
> > IMHO _bt_first() fucntion used to find first item in a scan should
> > be changed to work well in case of backward positioning.
> >
> > I think this change also gives the partial solution for the problem
> > [ [HACKERS] Cursor Movement - Past the End ] reported by
> > David Hartwig.
> >
> > I have a sample code for this change.
> > I can send it if someone want to check or test it.
> >
> > Thanks.
> >
> > Hiroshi Inoue
> > Inoue@tpf.co.jp
> >
> >
>
>
> --
> Bruce Momjian | http://www.op.net/~candle
> maillist@candle.pha.pa.us | (610) 853-3000
> + If your life is a hard drive, | 830 Blythe Avenue
> + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
>
>
--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #
Added to TODO: * Have optimizer take LIMIT into account when considering index scans > Hannu Krosing wrote: > > > > > Jan Wieck wrote: > > > > > > > > > > > Hi PostgreSQL hackers > > > > > > > > As we are again approaching the beta (feature freeze), > > > > I will ask my ordinary question ;) > > > > > > > > Is the patch by Jan that eliminated the duplicate sort node in case it > > > > was redundant included in 6.5 ? > > > > > > Sorry, > > > > > > I missed to put it into after v6.4 release. And since it > > > wasn't there during v6.5 development, I would not put it in > > > now. > > > > > > Note that it wasn't in the v6.4 feature patches either, so it > > > isn't tested enough to get released. > > > > But if it is not relesed it will _never_ be tested enough ... > > > > As we are just going into beta, not relese, I would suggest to put > > it in now, and back out if it relly breaks anything. > > > > I have been using it with 6.4 almost since the relese an have > > seen no problems - in fact it solved a big problem and provided about > > 1000X speedup for certain queries (a fraction of second instead of > > 6 minutes) , not to mention avoiding backend crashes due to disk space > > exhaustion. > > > > And it did not break anything in regression tests either, the only > > argument then was that there is nothing in regression tests that > > could possibly be broken by it ;) > > > > I greatly prefer it over my previous method of doing the same on the > > client side (issuing an EXPLAIN, parsing it to see if it is SORT on > > INDEX SCAN, and omitting the ORDER BY if it is) > > > > Also, not having it greatly diminishes the value of LIMIT. > > Ok ok ok - OK. You got me, I'll go ahead and put it in. > > > > > I agree that it is a hack and only a partial solution and that in > > ideal world the optimiser would also know about sort nodes. > > First the executor must know better how to handle LIMIT's > OFFSET. For now it processes the query until OFFSET is > reached, simply suppressing the in fact produced result > tuples in the output. The it stops sending if the LIMIT count > is reached. For joins or other complex things, it has no > chance to do something different. But for an indexed single > table scan, where ALL the qualifications are done on the > index, it should handle the OFFSET by skipping index tuples > only. > > Second the optimizer must take LIMIT into account and > depending on the known number of tuples, LIMIT and OFFSET > produce an index scan even if the query isn't qualified at > all but has an ORDER BY clause matched by the index. > > These two features would finally solve your huge table > problems. > > > Jan > > -- > > #======================================================================# > # It's easier to get forgiveness for being wrong than for being right. # > # Let's break this rule - forgive me. # > #======================================== jwieck@debis.com (Jan Wieck) # > > > > -- Bruce Momjian | http://www.op.net/~candle maillist@candle.pha.pa.us | (610) 853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania19026