help bug and comment char.

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This syntax help is out of date.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. We also support
double-slashes as comments, e.g.:
-- This is a standard SQL comment
// And this is another supported 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, Pennsylvania 19026

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, Pennsylvania 19026

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, Pennsylvania 19026

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, Pennsylvania 19026

Why don't you regress test it on the CURRENT tree and if it doesn't
break anything submit it? I thought that's what Beta was for (to get
the bugs worked out of the new features), but I'll trust your judgement
on what you think it'll break.
-DEJ

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, Pennsylvania 19026

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, Pennsylvania 19026

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, Pennsylvania 19026

-----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

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) #

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