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Hi list.

I've mostly used Oracle in the past, but for a web-project I took the
opportunity to try Postgres.

When a select is done in Oracle, it first checks if the select is cached
(ie parsed tree, optimizer choices & such). It does this by
[functionality equal to] a byte to byte compare with the other sql strings.

select a from b where c = 1
select a from b where c = 2

....will thus force a hard parse on the second select. But if using bind
variables it wont as the string stored is something like

select a from b where c = ?

Which will be the same as the second call. There is quite a big
difference in performance using bind variables.

Does Postgres work the same? Where can I go for more info?

Oracle recently gave some money to Zend to make proper Oracle support
for PHP. In that interface they use bind variables. Apart from greater
speed, sqlinjection becomes history as well.

Best regards,
Marcus


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Marcus Engene <mengpg@engene.se> writes:

> Which will be the same as the second call. There is quite a big
> difference in performance using bind variables.
>
> Does Postgres work the same? Where can I go for more info?

You can do this (or close to it) but you need to explicitly PREPARE
the query (or use the protocol-level prepare, which some client
libraries will do for you). See the SQL documentation for PREPARE.

-Doug

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PostgreSQL combines both parses into one, so every new query is
effectively a hard parse (unless it's prepared, then there is no parse
or optimization at all).

On Tue, Nov 15, 2005 at 07:33:46PM +0100, Marcus Engene wrote:
> Hi list.
>
> I've mostly used Oracle in the past, but for a web-project I took the
> opportunity to try Postgres.
>
> When a select is done in Oracle, it first checks if the select is cached
> (ie parsed tree, optimizer choices & such). It does this by
> [functionality equal to] a byte to byte compare with the other sql strings.
>
> select a from b where c = 1
> select a from b where c = 2
>
> ...will thus force a hard parse on the second select. But if using bind
> variables it wont as the string stored is something like
>
> select a from b where c = ?
>
> Which will be the same as the second call. There is quite a big
> difference in performance using bind variables.
>
> Does Postgres work the same? Where can I go for more info?
>
> Oracle recently gave some money to Zend to make proper Oracle support
> for PHP. In that interface they use bind variables. Apart from greater
> speed, sqlinjection becomes history as well.
>
> Best regards,
> Marcus
>
>
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> TIP 6: explain analyze is your friend
>

--
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

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In some cases, Oracle will also replace literals with bind variables so that
it can perform a sort-of-bind-value soft parse later.

On 11/15/05, Jim C. Nasby <jnasby@pervasive.com> wrote:
>
> PostgreSQL combines both parses into one, so every new query is
> effectively a hard parse (unless it's prepared, then there is no parse
> or optimization at all).
>
> On Tue, Nov 15, 2005 at 07:33:46PM +0100, Marcus Engene wrote:
> > Hi list.
> >
> > I've mostly used Oracle in the past, but for a web-project I took the
> > opportunity to try Postgres.
> >
> > When a select is done in Oracle, it first checks if the select is cached
> > (ie parsed tree, optimizer choices & such). It does this by
> > [functionality equal to] a byte to byte compare with the other sql
> strings.
> >
> > select a from b where c = 1
> > select a from b where c = 2
> >
> > ...will thus force a hard parse on the second select. But if using bind
> > variables it wont as the string stored is something like
> >
> > select a from b where c = ?
> >
> > Which will be the same as the second call. There is quite a big
> > difference in performance using bind variables.
> >
> > Does Postgres work the same? Where can I go for more info?
> >
> > Oracle recently gave some money to Zend to make proper Oracle support
> > for PHP. In that interface they use bind variables. Apart from greater
> > speed, sqlinjection becomes history as well.
> >
> > Best regards,
> > Marcus
> >
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 6: explain analyze is your friend
> >
>
> --
> 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
>
> ---------------------------(end of broadcast)---------------------------
> TIP 3: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faq
>

> > Oracle recently gave some money to Zend to make proper Oracle support
> > for PHP. In that interface they use bind variables. Apart from
> greater
> > speed, sqlinjection becomes history as well.

I did the same for PostgreSQL for PHP 5.1.

http://au3.php.net/manual/en/functio...ery-params.php

Chris


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Douglas McNaught wrote:
>>Which will be the same as the second call. There is quite a big
>>difference in performance using bind variables.
>>
>>Does Postgres work the same? Where can I go for more info?
>
> You can do this (or close to it) but you need to explicitly PREPARE
> the query (or use the protocol-level prepare, which some client
> libraries will do for you). See the SQL documentation for PREPARE.
>
> -Doug

Hi,

But this is of no use in a web-context. According to the docs, this
prepare is per session.

This sql cache I think is a really good thing. Is there a reason
Postgres hasn't got it? Would it be very hard to implement? From
a naive perspective; make a hashvalue from the sql-string to
quickly find the cached one, a "last used"-list for keeping
track of which to delete when cache full etc seems close to
trivial. Does the architecture/internal flow make it hard
actually reuse the query data structure?

Thanks for the answer.

Best regards,
Marcus

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On Wed, Nov 16, 2005 at 09:56:44AM +0100, Marcus Engene wrote:
> Douglas McNaught wrote:
> >You can do this (or close to it) but you need to explicitly PREPARE
> >the query (or use the protocol-level prepare, which some client
> >libraries will do for you). See the SQL documentation for PREPARE.
>
> But this is of no use in a web-context. According to the docs, this
> prepare is per session.

Unless you use something like pgpool, in which case a single session
may include multiple requests.

> This sql cache I think is a really good thing. Is there a reason
> Postgres hasn't got it? Would it be very hard to implement? From
> a naive perspective; make a hashvalue from the sql-string to
> quickly find the cached one, a "last used"-list for keeping
> track of which to delete when cache full etc seems close to
> trivial. Does the architecture/internal flow make it hard
> actually reuse the query data structure?

It's hard to reuse the structure. Also, things like search_path mean
that the same query text can mean completely different things in
different backends. Most of the time it's planning that dominates, not
parsing so storing just the parser output seems somewhat useless.

Unless you've thought of a new way to do 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.

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Christopher Kings-Lynne wrote:
>> > Oracle recently gave some money to Zend to make proper Oracle
>> support
>> > for PHP. In that interface they use bind variables. Apart from
>> greater
>> > speed, sqlinjection becomes history as well.
>
>
> I did the same for PostgreSQL for PHP 5.1.
>
> http://au3.php.net/manual/en/functio...ery-params.php
>
> Chris

Brilliant! I'll upgrade to 5.1 for this reason alone!

Best regards,
Marcus


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Martijn van Oosterhout wrote:
>>But this is of no use in a web-context. According to the docs, this
>>prepare is per session.
>
> Unless you use something like pgpool, in which case a single session
> may include multiple requests.

ok. Good point.

>>This sql cache I think is a really good thing. Is there a reason
>>Postgres hasn't got it? Would it be very hard to implement? From
>>a naive perspective; make a hashvalue from the sql-string to
>>quickly find the cached one, a "last used"-list for keeping
>>track of which to delete when cache full etc seems close to
>>trivial. Does the architecture/internal flow make it hard
>>actually reuse the query data structure?
>
> It's hard to reuse the structure. Also, things like search_path mean
> that the same query text can mean completely different things in
> different backends. Most of the time it's planning that dominates, not
> parsing so storing just the parser output seems somewhat useless.

Of course I didn't mean only the parse was to be saved. The planning
goes there too.

Thanks for the explanation.

> Have a nice day,

The same!

Marcus

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Martijn van Oosterhout <kleptog@svana.org> writes:
> Unless you use something like pgpool, in which case a single session
> may include multiple requests.

Actually, I've found pgpool to be no better when it comes to using
real prepared queries---there's no guarantee that any given request is
going to connect to the same pgpool process as before, so it won't
have the prepared request.

Mike

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