setting per-database/role parameters checks them against wrong context

Example:

create temporary table foo (a int);
insert into foo values (1);
alter role peter set temp_buffers = 120;
ERROR: 22023: invalid value for parameter "temp_buffers": 120
DETAIL: "temp_buffers" cannot be changed after any temporary tables
have been accessed in the session.

Another example:

set log_statement_stats = on;
alter role peter set log_parser_stats = on;
ERROR: 22023: invalid value for parameter "log_parser_stats": 1
DETAIL: Cannot enable parameter when "log_statement_stats" is true.

Another example is that in <=9.1, ALTER DATABASE ... SET search_path
would check the existence of the schema in the current database, but
that was done away with in 9.2.

The first example could probably be fixed if check_temp_buffers() paid
attention to the GucSource, but in the second case and in general there
doesn't seem to be a way to distinguish "assigning per-database setting"
and "enacting per-database setting" as a source.

Ideas?

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> Example:
> create temporary table foo (a int);
> insert into foo values (1);
> alter role peter set temp_buffers = 120;
> ERROR: 22023: invalid value for parameter "temp_buffers": 120
> DETAIL: "temp_buffers" cannot be changed after any temporary tables
> have been accessed in the session.

> Another example:

> set log_statement_stats = on;
> alter role peter set log_parser_stats = on;
> ERROR: 22023: invalid value for parameter "log_parser_stats": 1
> DETAIL: Cannot enable parameter when "log_statement_stats" is true.

> Another example is that in <=9.1, ALTER DATABASE ... SET search_path
> would check the existence of the schema in the current database, but
> that was done away with in 9.2.

> The first example could probably be fixed if check_temp_buffers() paid
> attention to the GucSource, but in the second case and in general there
> doesn't seem to be a way to distinguish "assigning per-database setting"
> and "enacting per-database setting" as a source.

> Ideas?

Perhaps instead of trying to solve the problem as stated, it would be
more useful to put the effort into getting rid of context-sensitive
restrictions on GUC settings. Neither of the examples above seem
particularly essential - they are just protecting incomplete
implementations.

regards, tom lane

On Fri, Sep 28, 2012 at 7:10 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>> Example:
>> create temporary table foo (a int);
>> insert into foo values (1);
>> alter role peter set temp_buffers = 120;
>> ERROR: 22023: invalid value for parameter "temp_buffers": 120
>> DETAIL: "temp_buffers" cannot be changed after any temporary tables
>> have been accessed in the session.
>
>> Another example:
>
>> set log_statement_stats = on;
>> alter role peter set log_parser_stats = on;
>> ERROR: 22023: invalid value for parameter "log_parser_stats": 1
>> DETAIL: Cannot enable parameter when "log_statement_stats" is true.
>
>> Another example is that in <=9.1, ALTER DATABASE ... SET search_path
>> would check the existence of the schema in the current database, but
>> that was done away with in 9.2.
>
>> The first example could probably be fixed if check_temp_buffers() paid
>> attention to the GucSource, but in the second case and in general there
>> doesn't seem to be a way to distinguish "assigning per-database setting"
>> and "enacting per-database setting" as a source.
>
>> Ideas?
>
> Perhaps instead of trying to solve the problem as stated, it would be
> more useful to put the effort into getting rid of context-sensitive
> restrictions on GUC settings. Neither of the examples above seem
> particularly essential - they are just protecting incomplete
> implementations.

The check_temp_buffers() problem seems like a regression and blocks us
from upgrading to 9.2. The use case are functions that set
temp_buffers and occasionally are called in a series from a parent
session. The work around is... a lot of work.

I'd appreciate it if we could fix the temp_buffers issue, and I
support getting rid of context-sensitive restrictions. :)

-selena

--
http://chesnok.com

Selena Deckelmann <selena(at)chesnok(dot)com> writes:
> The check_temp_buffers() problem seems like a regression and blocks us
> from upgrading to 9.2. The use case are functions that set
> temp_buffers and occasionally are called in a series from a parent
> session. The work around is... a lot of work.

Uh ... how is that a regression? AFAIK it's been that way right along.

regards, tom lane

> Uh ... how is that a regression? AFAIK it's been that way right along.

No, it hasn't. I currently have an application whose functions, each of
which sets temp_buffers, works fine under 9.0 and ERRORs out under 9.2.
It's blocking an upgrade.

This is new.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com

On Mon, Oct 1, 2012 at 1:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Selena Deckelmann <selena(at)chesnok(dot)com> writes:
>> The check_temp_buffers() problem seems like a regression and blocks us
>> from upgrading to 9.2. The use case are functions that set
>> temp_buffers and occasionally are called in a series from a parent
>> session. The work around is... a lot of work.
>
> Uh ... how is that a regression? AFAIK it's been that way right along.

We're running 9.0 - looks like it changed in 9.1, last revision to the
relevant line was 6/2011. The group decided not to upgrade to 9.1 last
year, but was going to just go directly to 9.2 in the next few weeks.

-selena

--
http://chesnok.com

On Mon, Oct 1, 2012 at 1:37 PM, Selena Deckelmann <selena(at)chesnok(dot)com> wrote:
> On Mon, Oct 1, 2012 at 1:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Selena Deckelmann <selena(at)chesnok(dot)com> writes:
>>> The check_temp_buffers() problem seems like a regression and blocks us
>>> from upgrading to 9.2. The use case are functions that set
>>> temp_buffers and occasionally are called in a series from a parent
>>> session. The work around is... a lot of work.
>>
>> Uh ... how is that a regression? AFAIK it's been that way right along.
>
> We're running 9.0 - looks like it changed in 9.1, last revision to the
> relevant line was 6/2011. The group decided not to upgrade to 9.1 last
> year, but was going to just go directly to 9.2 in the next few weeks.

And, I was basing the regression comment on the documentation for
temp_buffers: "The setting can be changed within individual sessions,
but only before the first use of temporary tables within the session;
subsequent attempts to change the value will have no effect on that
session." This statement has been there since at least 8.1.

A warning, and then not failing seems more appropriate than an error,
given the documented behavior.

-selena

--
http://chesnok.com

On Mon, Oct 1, 2012 at 2:28 PM, Selena Deckelmann <selena(at)chesnok(dot)com> wrote:
> On Mon, Oct 1, 2012 at 1:37 PM, Selena Deckelmann <selena(at)chesnok(dot)com> wrote:
>> On Mon, Oct 1, 2012 at 1:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Selena Deckelmann <selena(at)chesnok(dot)com> writes:
>>>> The check_temp_buffers() problem seems like a regression and blocks us
>>>> from upgrading to 9.2. The use case are functions that set
>>>> temp_buffers and occasionally are called in a series from a parent
>>>> session. The work around is... a lot of work.
>>>
>>> Uh ... how is that a regression? AFAIK it's been that way right along.
>>
>> We're running 9.0 - looks like it changed in 9.1, last revision to the
>> relevant line was 6/2011. The group decided not to upgrade to 9.1 last
>> year, but was going to just go directly to 9.2 in the next few weeks.
>
> And, I was basing the regression comment on the documentation for
> temp_buffers: "The setting can be changed within individual sessions,
> but only before the first use of temporary tables within the session;
> subsequent attempts to change the value will have no effect on that
> session." This statement has been there since at least 8.1.
>
> A warning, and then not failing seems more appropriate than an error,
> given the documented behavior.

I tried out a few things, and then realized that perhaps just adding
PGC_S_SESSION to the list of sources that are at elevel WARNING
partially fixes this.

This doesn't fix the issue with log_statement_stats, but it makes the
behavior of temp_buffers the documented behavior (no longer errors
out in a transaction), while still warning the user.

-selena

--
http://chesnok.com

On Sat, Oct 6, 2012 at 02:20:53PM -0700, Selena Deckelmann wrote:
> On Mon, Oct 1, 2012 at 2:28 PM, Selena Deckelmann <selena(at)chesnok(dot)com> wrote:
> > On Mon, Oct 1, 2012 at 1:37 PM, Selena Deckelmann <selena(at)chesnok(dot)com> wrote:
> >> On Mon, Oct 1, 2012 at 1:00 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >>> Selena Deckelmann <selena(at)chesnok(dot)com> writes:
> >>>> The check_temp_buffers() problem seems like a regression and blocks us
> >>>> from upgrading to 9.2. The use case are functions that set
> >>>> temp_buffers and occasionally are called in a series from a parent
> >>>> session. The work around is... a lot of work.
> >>>
> >>> Uh ... how is that a regression? AFAIK it's been that way right along.
> >>
> >> We're running 9.0 - looks like it changed in 9.1, last revision to the
> >> relevant line was 6/2011. The group decided not to upgrade to 9.1 last
> >> year, but was going to just go directly to 9.2 in the next few weeks.
> >
> > And, I was basing the regression comment on the documentation for
> > temp_buffers: "The setting can be changed within individual sessions,
> > but only before the first use of temporary tables within the session;
> > subsequent attempts to change the value will have no effect on that
> > session." This statement has been there since at least 8.1.
> >
> > A warning, and then not failing seems more appropriate than an error,
> > given the documented behavior.
>
> I tried out a few things, and then realized that perhaps just adding
> PGC_S_SESSION to the list of sources that are at elevel WARNING
> partially fixes this.
>
> This doesn't fix the issue with log_statement_stats, but it makes the
> behavior of temp_buffers the documented behavior (no longer errors
> out in a transaction), while still warning the user.

> diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
> index 6b202e0..0677059 100644
> --- a/src/backend/utils/misc/guc.c
> +++ b/src/backend/utils/misc/guc.c
> @@ -5150,7 +5150,7 @@ set_config_option(const char *name, const char *value,
> elevel = IsUnderPostmaster ? DEBUG3 : LOG;
> }
> else if (source == PGC_S_DATABASE || source == PGC_S_USER ||
> - source == PGC_S_DATABASE_USER)
> + source == PGC_S_DATABASE_USER || source == PG_S_SESSION)
> elevel = WARNING;
> else
> elevel = ERROR;

Is there any opinion on whether we need this patch? It basically allows
SET from a session to issue a warning rather than an error. This is
certainly a much larger change than just fixing temp_buffers. The user
complaint was that functions were setting temp_buffers and getting
errors because temp table has already been used:

The setting can be changed within individual sessions, but only
before the first use of temporary tables within the session;
subsequent attempts to change the value will have no effect on
that session.

The full thread is here:

http://www.postgresql.org/message-id/1348802984.3584.22.camel@vanquo.pezone.net

Seems this changed in PG 9.1.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +

Bruce Momjian <bruce(at)momjian(dot)us> writes:
>> diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
>> index 6b202e0..0677059 100644
>> --- a/src/backend/utils/misc/guc.c
>> +++ b/src/backend/utils/misc/guc.c
>> @@ -5150,7 +5150,7 @@ set_config_option(const char *name, const char *value,
>> elevel = IsUnderPostmaster ? DEBUG3 : LOG;
>> }
>> else if (source == PGC_S_DATABASE || source == PGC_S_USER ||
>> - source == PGC_S_DATABASE_USER)
>> + source == PGC_S_DATABASE_USER || source == PG_S_SESSION)
>> elevel = WARNING;
>> else
>> elevel = ERROR;

> Is there any opinion on whether we need this patch? It basically allows
> SET from a session to issue a warning rather than an error.

Surely this is a completely horrid idea. It doesn't "allow" SET to
throw a warning, it changes all interactive-SET cases from ERROR to
WARNING. That's a whole lot of collateral damage to fix a very narrow
case that's not even there anymore.

regards, tom lane

On Fri, Jan 25, 2013 at 03:35:59PM -0500, Tom Lane wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
> >> diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
> >> index 6b202e0..0677059 100644
> >> --- a/src/backend/utils/misc/guc.c
> >> +++ b/src/backend/utils/misc/guc.c
> >> @@ -5150,7 +5150,7 @@ set_config_option(const char *name, const char *value,
> >> elevel = IsUnderPostmaster ? DEBUG3 : LOG;
> >> }
> >> else if (source == PGC_S_DATABASE || source == PGC_S_USER ||
> >> - source == PGC_S_DATABASE_USER)
> >> + source == PGC_S_DATABASE_USER || source == PG_S_SESSION)
> >> elevel = WARNING;
> >> else
> >> elevel = ERROR;
>
> > Is there any opinion on whether we need this patch? It basically allows
> > SET from a session to issue a warning rather than an error.
>
> Surely this is a completely horrid idea. It doesn't "allow" SET to
> throw a warning, it changes all interactive-SET cases from ERROR to
> WARNING. That's a whole lot of collateral damage to fix a very narrow
> case that's not even there anymore.

Agreed.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +