Обсуждение: Delete rule does not prevent truncate

Hi,

I very much hope this is an accidental bug rather than a deliberate feature !

PostgreSQL 9.4.4

create rule no_auditupd as on update to app_security.app_audit do
instead nothing;
create rule no_auditdel as on delete to app_security.app_audit do
instead nothing;

\d+  app_security.app_audit
<snip>
Rules:
    no_auditdel AS
    ON DELETE TO app_security.app_audit DO INSTEAD NOTHING
    no_auditupd AS
    ON UPDATE TO app_security.app_audit DO INSTEAD NOTHING

The truncate trashes the whole table  ;-(

According to the FabulousManual(TM) :
event : The event is one of SELECT, INSERT, UPDATE, or DELETE.

Thus I can't create a rule to "do nothing" on truncates, thus I am stuck !

On 07/22/2015 06:13 AM, Tim Smith wrote:
> Melvin,
>
> May I point out that the manual states :
> "TRUNCATE quickly removes all rows from a set of tables. It has the same
> effect as an unqualified DELETE on each table"
>
> Thus, if you are telling me to effectively think of TRUNCATE as an alias
> to DELETE, then I would think its not entirely unreasonable of me to
> expect a rule preventing DELETE to also cover truncate, since the rule
> would no doubt prevent an unqualified DELETE, would it not ?!?

If  you go further down into the Notes section you find:

"TRUNCATE will not fire any ON DELETE triggers that might exist for the
tables. But it will fire ON TRUNCATE triggers. If ON TRUNCATE triggers
are defined for any of the tables, then all BEFORE TRUNCATE triggers are
fired before any truncation happens, and all AFTER TRUNCATE triggers are
fired after the last truncation is performed and any sequences are
reset. The triggers will fire in the order that the tables are to be
processed (first those listed in the command, and then any that were
added due to cascading).
Warning

TRUNCATE is not MVCC-safe (see Chapter 13 for general information about
MVCC). After truncation, the table will appear empty to all concurrent
transactions, even if they are using a snapshot taken before the
truncation occurred. This will only be an issue for a transaction that
did not access the truncated table before the truncation happened — any
transaction that has done so would hold at least an ACCESS SHARE lock,
which would block TRUNCATE until that transaction completes. So
truncation will not cause any apparent inconsistency in the table
contents for successive queries on the same table, but it could cause
visible inconsistency between the contents of the truncated table and
other tables in the database.

"


TRUNCATE is when you want fast over safety.

>
> On 22 July 2015 at 14:03, Melvin Davidson <melvin6925@gmail.com
> <mailto:melvin6925@gmail.com>> wrote:
>
>     Actually, if you use a TRIGGER instead of rule, you can handle this.
>     The manual states event can be:
>
>     INSERT
>     UPDATE [ OFcolumn_name  [, ... ] ]
>     DELETE
>     *TRUNCATE <-----*
>
>     http://www.postgresql.org/docs/9.4/interactive/sql-createtrigger.html
>
>     I suggest you review carefully.
>
>     On Wed, Jul 22, 2015 at 8:53 AM, Tim Smith
>     <randomdev4+postgres@gmail.com
>     <mailto:randomdev4+postgres@gmail.com>> wrote:
>
>         Hi,
>
>         I very much hope this is an accidental bug rather than a
>         deliberate feature !
>
>         PostgreSQL 9.4.4
>
>         create rule no_auditupd as on update to app_security.app_audit do
>         instead nothing;
>         create rule no_auditdel as on delete to app_security.app_audit do
>         instead nothing;
>
>         \d+  app_security.app_audit
>         <snip>
>         Rules:
>              no_auditdel AS
>              ON DELETE TO app_security.app_audit DO INSTEAD NOTHING
>              no_auditupd AS
>              ON UPDATE TO app_security.app_audit DO INSTEAD NOTHING
>
>         The truncate trashes the whole table  ;-(
>
>         According to the FabulousManual(TM) :
>         event : The event is one of SELECT, INSERT, UPDATE, or DELETE.
>
>         Thus I can't create a rule to "do nothing" on truncates, thus I
>         am stuck !
>
>
>         --
>         Sent via pgsql-general mailing list
>         (pgsql-general@postgresql.org <mailto:pgsql-general@postgresql.org>)
>         To make changes to your subscription:
>         http://www.postgresql.org/mailpref/pgsql-general
>
>
>
>
>     --
>     *Melvin Davidson*
>     I reserve the right to fantasize.  Whether or not you
>     wish to share my fantasy is entirely up to you.
>
>


--
Adrian Klaver
adrian.klaver@aklaver.com

Adrian,

It still doesn't make much sense, especially as given the rather
obscure and questionable design decision of allowing triggers to refer
to truncate ops, but not allowing rules to refer to truncate ops !!!

Surely either you say "look, truncate is truncate, its there for one
purpose and one purpose only".    Or otherwise, you should handle it
consistently across the database, i.e. if you're going to allow
triggers interact with truncates, then you should allow rules to
interact with truncates.    It really doesn't make much sense to adopt
a pick and choose mentality !

On 22 July 2015 at 14:19, Adrian Klaver <adrian.klaver@aklaver.com> wrote:
> On 07/22/2015 06:13 AM, Tim Smith wrote:
>>
>> Melvin,
>>
>> May I point out that the manual states :
>> "TRUNCATE quickly removes all rows from a set of tables. It has the same
>> effect as an unqualified DELETE on each table"
>>
>> Thus, if you are telling me to effectively think of TRUNCATE as an alias
>> to DELETE, then I would think its not entirely unreasonable of me to
>> expect a rule preventing DELETE to also cover truncate, since the rule
>> would no doubt prevent an unqualified DELETE, would it not ?!?
>
>
> If  you go further down into the Notes section you find:
>
> "TRUNCATE will not fire any ON DELETE triggers that might exist for the
> tables. But it will fire ON TRUNCATE triggers. If ON TRUNCATE triggers are
> defined for any of the tables, then all BEFORE TRUNCATE triggers are fired
> before any truncation happens, and all AFTER TRUNCATE triggers are fired
> after the last truncation is performed and any sequences are reset. The
> triggers will fire in the order that the tables are to be processed (first
> those listed in the command, and then any that were added due to cascading).
> Warning
>
> TRUNCATE is not MVCC-safe (see Chapter 13 for general information about
> MVCC). After truncation, the table will appear empty to all concurrent
> transactions, even if they are using a snapshot taken before the truncation
> occurred. This will only be an issue for a transaction that did not access
> the truncated table before the truncation happened — any transaction that
> has done so would hold at least an ACCESS SHARE lock, which would block
> TRUNCATE until that transaction completes. So truncation will not cause any
> apparent inconsistency in the table contents for successive queries on the
> same table, but it could cause visible inconsistency between the contents of
> the truncated table and other tables in the database.
>
> "
>
>
> TRUNCATE is when you want fast over safety.
>
>>
>> On 22 July 2015 at 14:03, Melvin Davidson <melvin6925@gmail.com
>> <mailto:melvin6925@gmail.com>> wrote:
>>
>>     Actually, if you use a TRIGGER instead of rule, you can handle this.
>>     The manual states event can be:
>>
>>     INSERT
>>     UPDATE [ OFcolumn_name  [, ... ] ]
>>     DELETE
>>     *TRUNCATE <-----*
>>
>>     http://www.postgresql.org/docs/9.4/interactive/sql-createtrigger.html
>>
>>     I suggest you review carefully.
>>
>>     On Wed, Jul 22, 2015 at 8:53 AM, Tim Smith
>>     <randomdev4+postgres@gmail.com
>>     <mailto:randomdev4+postgres@gmail.com>> wrote:
>>
>>         Hi,
>>
>>         I very much hope this is an accidental bug rather than a
>>         deliberate feature !
>>
>>         PostgreSQL 9.4.4
>>
>>         create rule no_auditupd as on update to app_security.app_audit do
>>         instead nothing;
>>         create rule no_auditdel as on delete to app_security.app_audit do
>>         instead nothing;
>>
>>         \d+  app_security.app_audit
>>         <snip>
>>         Rules:
>>              no_auditdel AS
>>              ON DELETE TO app_security.app_audit DO INSTEAD NOTHING
>>              no_auditupd AS
>>              ON UPDATE TO app_security.app_audit DO INSTEAD NOTHING
>>
>>         The truncate trashes the whole table  ;-(
>>
>>         According to the FabulousManual(TM) :
>>         event : The event is one of SELECT, INSERT, UPDATE, or DELETE.
>>
>>         Thus I can't create a rule to "do nothing" on truncates, thus I
>>         am stuck !
>>
>>
>>         --
>>         Sent via pgsql-general mailing list
>>         (pgsql-general@postgresql.org
>> <mailto:pgsql-general@postgresql.org>)
>>         To make changes to your subscription:
>>         http://www.postgresql.org/mailpref/pgsql-general
>>
>>
>>
>>
>>     --
>>     *Melvin Davidson*
>>     I reserve the right to fantasize.  Whether or not you
>>     wish to share my fantasy is entirely up to you.
>>
>>
>
>
> --
> Adrian Klaver
> adrian.klaver@aklaver.com

On 07/22/2015 06:24 AM, Tim Smith wrote:
> Adrian,
>
> It still doesn't make much sense, especially as given the rather
> obscure and questionable design decision of allowing triggers to refer
> to truncate ops, but not allowing rules to refer to truncate ops !!!
>
> Surely either you say "look, truncate is truncate, its there for one
> purpose and one purpose only".    Or otherwise, you should handle it
> consistently across the database, i.e. if you're going to allow
> triggers interact with truncates, then you should allow rules to
> interact with truncates.    It really doesn't make much sense to adopt
> a pick and choose mentality !

All I know is that TRUNCATE is a shortcut and RULEs do not understand it
and TRIGGERs do. My guess is the answer somewhere in here:

http://www.postgresql.org/docs/9.4/interactive/rules.html

Word of advice, take two aspirin before reading above.

At any rate,  I have personally found using triggers results in less
surprises then using rules.

>
> On 22 July 2015 at 14:19, Adrian Klaver <adrian.klaver@aklaver.com> wrote:
>> On 07/22/2015 06:13 AM, Tim Smith wrote:
>>>
>>> Melvin,
>>>
>>> May I point out that the manual states :
>>> "TRUNCATE quickly removes all rows from a set of tables. It has the same
>>> effect as an unqualified DELETE on each table"
>>>
>>> Thus, if you are telling me to effectively think of TRUNCATE as an alias
>>> to DELETE, then I would think its not entirely unreasonable of me to
>>> expect a rule preventing DELETE to also cover truncate, since the rule
>>> would no doubt prevent an unqualified DELETE, would it not ?!?
>>
>>
>> If  you go further down into the Notes section you find:
>>
>> "TRUNCATE will not fire any ON DELETE triggers that might exist for the
>> tables. But it will fire ON TRUNCATE triggers. If ON TRUNCATE triggers are
>> defined for any of the tables, then all BEFORE TRUNCATE triggers are fired
>> before any truncation happens, and all AFTER TRUNCATE triggers are fired
>> after the last truncation is performed and any sequences are reset. The
>> triggers will fire in the order that the tables are to be processed (first
>> those listed in the command, and then any that were added due to cascading).
>> Warning
>>
>> TRUNCATE is not MVCC-safe (see Chapter 13 for general information about
>> MVCC). After truncation, the table will appear empty to all concurrent
>> transactions, even if they are using a snapshot taken before the truncation
>> occurred. This will only be an issue for a transaction that did not access
>> the truncated table before the truncation happened — any transaction that
>> has done so would hold at least an ACCESS SHARE lock, which would block
>> TRUNCATE until that transaction completes. So truncation will not cause any
>> apparent inconsistency in the table contents for successive queries on the
>> same table, but it could cause visible inconsistency between the contents of
>> the truncated table and other tables in the database.
>>
>> "
>>
>>
>> TRUNCATE is when you want fast over safety.
>>
>>>
>>> On 22 July 2015 at 14:03, Melvin Davidson <melvin6925@gmail.com
>>> <mailto:melvin6925@gmail.com>> wrote:
>>>
>>>      Actually, if you use a TRIGGER instead of rule, you can handle this.
>>>      The manual states event can be:
>>>
>>>      INSERT
>>>      UPDATE [ OFcolumn_name  [, ... ] ]
>>>      DELETE
>>>      *TRUNCATE <-----*
>>>
>>>      http://www.postgresql.org/docs/9.4/interactive/sql-createtrigger.html
>>>
>>>      I suggest you review carefully.
>>>
>>>      On Wed, Jul 22, 2015 at 8:53 AM, Tim Smith
>>>      <randomdev4+postgres@gmail.com
>>>      <mailto:randomdev4+postgres@gmail.com>> wrote:
>>>
>>>          Hi,
>>>
>>>          I very much hope this is an accidental bug rather than a
>>>          deliberate feature !
>>>
>>>          PostgreSQL 9.4.4
>>>
>>>          create rule no_auditupd as on update to app_security.app_audit do
>>>          instead nothing;
>>>          create rule no_auditdel as on delete to app_security.app_audit do
>>>          instead nothing;
>>>
>>>          \d+  app_security.app_audit
>>>          <snip>
>>>          Rules:
>>>               no_auditdel AS
>>>               ON DELETE TO app_security.app_audit DO INSTEAD NOTHING
>>>               no_auditupd AS
>>>               ON UPDATE TO app_security.app_audit DO INSTEAD NOTHING
>>>
>>>          The truncate trashes the whole table  ;-(
>>>
>>>          According to the FabulousManual(TM) :
>>>          event : The event is one of SELECT, INSERT, UPDATE, or DELETE.
>>>
>>>          Thus I can't create a rule to "do nothing" on truncates, thus I
>>>          am stuck !
>>>
>>>
>>>          --
>>>          Sent via pgsql-general mailing list
>>>          (pgsql-general@postgresql.org
>>> <mailto:pgsql-general@postgresql.org>)
>>>          To make changes to your subscription:
>>>          http://www.postgresql.org/mailpref/pgsql-general
>>>
>>>
>>>
>>>
>>>      --
>>>      *Melvin Davidson*
>>>      I reserve the right to fantasize.  Whether or not you
>>>      wish to share my fantasy is entirely up to you.
>>>
>>>
>>
>>
>> --
>> Adrian Klaver
>> adrian.klaver@aklaver.com
>
>


--
Adrian Klaver
adrian.klaver@aklaver.com

On 07/22/2015 06:13 AM, Tim Smith wrote:
> Melvin,
>
> May I point out that the manual states :
> "TRUNCATE quickly removes all rows from a set of tables. It has the same
> effect as an unqualified DELETE on each table"

This is actually wrong. The end result is the same but it does not in
any way have the same effect. And I will submit a patch.

TRUNCATE is NOT DELETE.

Sincerely,

JD

--
Command Prompt, Inc. - http://www.commandprompt.com/  503-667-4564
PostgreSQL Centered full stack support, consulting and development.
Announcing "I'm offended" is basically telling the world you can't
control your own emotions, so everyone else should do it for you.

On 07/22/2015 06:24 AM, Tim Smith wrote:
>
> Adrian,
>
> It still doesn't make much sense, especially as given the rather
> obscure and questionable design decision of allowing triggers to refer
> to truncate ops, but not allowing rules to refer to truncate ops !!!

Actually it makes perfect sense because rules are a feature for
compatibility (at this point) more than anything else. They are slower
than triggers, less flexible and widely considered something you only
use in very rare circumstances.

That and of course, patches are accepted if you feel it is a feature
worth having.

JD




--
Command Prompt, Inc. - http://www.commandprompt.com/  503-667-4564
PostgreSQL Centered full stack support, consulting and development.
Announcing "I'm offended" is basically telling the world you can't
control your own emotions, so everyone else should do it for you.

On 07/22/2015 08:42 AM, Geoff Winkless wrote:
> On 22 July 2015 at 16:32, Joshua D. Drake <jd@commandprompt.com
> <mailto:jd@commandprompt.com>>wrote:
>
>     This is actually wrong. The end result is the same but it does not
>     in any way have the same effect.
>
> ​
> "in any way"? ​
> ​I'd say in the primary way it has the same effect: all rows are removed
> from the table.

Thus the end result is the same as I said but the in practice effect is
quite different from a visibility, maintenance and programmability
perspective.

>
>     TRUNCATE is NOT DELETE.
>
>
> ​I don't think anyone is suggesting that it is.​

Except Tim Smith who started this thread.

JD

--
Command Prompt, Inc. - http://www.commandprompt.com/  503-667-4564
PostgreSQL Centered full stack support, consulting and development.
Announcing "I'm offended" is basically telling the world you can't
control your own emotions, so everyone else should do it for you.

So tell me guys, instead of bashing away at the fact I only quoted
half a sentence or whatever, how about you answer the following :

What exactly is was the design decision that lead to TRUNCATE being
supported by triggers but not by rules ?

I suspect that TRUNCATE was added to triggers because some dev thought
it would be a neat idea, and it was never implemented in rules as a
result of an accidental omission for <whatever reason> rather than a
deliberate design constraint.

On Thu, Jul 23, 2015 at 08:06:19AM +0100, Tim Smith wrote:
> What exactly is was the design decision that lead to TRUNCATE being
> supported by triggers but not by rules ?

There are two things.  First, probably the design decision was, "I
care about triggers."  TRUNCATE was added (I believe) in version 7.0,
and even then there was some caution indicated about the use of rules.
See for instance
http://www.postgresql.org/docs/7.0/static/rules19784.htm.  So you
might be partly right.

But second, it isn't clear what it would mean for TRUNCATE to be
supported by rules.  Rules do query parse tree rewriting.  That is,
they rewrite the query on the way through the system before they can
possibly have any effect, changing one SQL statement into
(effectively) a different one by the time it executes.  There is only
one possible effect from TRUNCATE, and that is to eliminate all the
data in the table.  I don't know what rewriting such a query would
mean.

Best regards,

A

--
Andrew Sullivan
ajs@crankycanuck.ca

On Thu, Jul 23, 2015 at 12:57:20PM +0100, Tim Smith wrote:
> It is important to realize that a rule is really a command transformation
> mechanism, or command macro. The transformation happens before the
> execution of the command starts. If you actually want an operation that
> fires independently for each physical row, you probably want to use a
> trigger, not a rule

Well, yes, but the discussion of the rules system in earlier manuals
was actually, I thought, somewhat more detailed; and it outlined what
rules really did, which was alter the command at the parse tree.
That's what I think the above is saying also, but it may not be quite
as plain.  So it's rather more like a statement-level trigger.

> Thus, I should not have to use a trigger for TRUNCATE because the "each
> row" concept does not apply.     Plus it makes perfect sense to want to
> transform the truncate command and transform into ignore

Well, yes, but really in this case you want a per-statement trigger,
and there's not the same distinction in rules, either.

I can't believe that people would reject a patch (though you should
ask on -hackers, not here); but you asked what was behind the design
decision and I told you.  But in general, the experience seems to be
that triggers are easier to get right (novice or no, _pace_ section
38.7).

Best regards,

A

--
Andrew Sullivan
ajs@crankycanuck.ca

On 2015-07-23 12:57:20 +0100, Tim Smith wrote:
> Thus, I should not have to use a trigger for TRUNCATE because the "each
> row" concept does not apply.     Plus it makes perfect sense to want to
> transform the truncate command and transform into ignore

That'd entirely defeat the point of TRUNCATE being fast.


Either way, this isn't going to change, so it seems a bit pointless to
continue arguing around it circles.

On 07/23/2015 04:57 AM, Tim Smith wrote:
> Andrew,
>
>  From the manual:
>
> It is important to realize that a rule is really a command
> transformation mechanism, or command macro. The transformation happens
> before the execution of the command starts. If you actually want an
> operation that fires independently for each physical row, you probably
> want to use a trigger, not a rule
>
>
> Thus, I should not have to use a trigger for TRUNCATE because the "each
> row" concept does not apply.     Plus it makes perfect sense to want to
> transform the truncate command and transform into ignore
>

Just in case it has not been made obvious yet, rules are silently
deprecated. They still exist because views depend on them, but it is
generally considered best practices to not use them outside that realm.
So if you want the rule behavior to change for TRUNCATE(if that is even
possible) you are fighting an uphill battle. You may pursue that fight
of course, but I would think you will get a quicker return on your time
if you just forget about using a RULE and stick to a TRIGGER instead.

--
Adrian Klaver
adrian.klaver@aklaver.com

On 07/23/2015 04:57 AM, Tim Smith wrote:

Andrew,

 From the manual:

It is important to realize that a rule is really a command
transformation mechanism, or command macro. The transformation happens
before the execution of the command starts. If you actually want an
operation that fires independently for each physical row, you probably
want to use a trigger, not a rule


Thus, I should not have to use a trigger for TRUNCATE because the "each
row" concept does not apply.     Plus it makes perfect sense to want to
transform the truncate command and transform into ignore

Just in case it has not been made obvious yet, rules are silently deprecated. They still exist because views depend on them, but it is generally considered best practices to not use them outside that realm. So if you want the rule behavior to change for TRUNCATE(if that is even possible) you are fighting an uphill battle. You may pursue that fight of course, but I would think you will get a quicker return on your time if you just forget about using a RULE and stick to a TRIGGER instead.

On 07/23/2015 11:15 AM, Rob Sargent wrote:
> On 07/23/2015 12:09 PM, Adrian Klaver wrote:
>> On 07/23/2015 04:57 AM, Tim Smith wrote:
>>> Andrew,
>>>
>>>  From the manual:
>>>
>>> It is important to realize that a rule is really a command
>>> transformation mechanism, or command macro. The transformation happens
>>> before the execution of the command starts. If you actually want an
>>> operation that fires independently for each physical row, you probably
>>> want to use a trigger, not a rule
>>>
>>>
>>> Thus, I should not have to use a trigger for TRUNCATE because the "each
>>> row" concept does not apply.     Plus it makes perfect sense to want to
>>> transform the truncate command and transform into ignore
>>>
>>
>> Just in case it has not been made obvious yet, rules are silently
>> deprecated. They still exist because views depend on them, but it is
>> generally considered best practices to not use them outside that
>> realm. So if you want the rule behavior to change for TRUNCATE(if that
>> is even possible) you are fighting an uphill battle. You may pursue
>> that fight of course, but I would think you will get a quicker return
>> on your time if you just forget about using a RULE and stick to a
>> TRIGGER instead.
>>
> Or change to using delete instead of truncate?
>

Well Tim has an ON DELETE rule:

http://www.postgresql.org/message-id/CA+HuS5G2bZYYOGTJrw+VosjUPO298swxuU=JOrFAv54UT7vniQ@mail.gmail.com

His expectation was that would also catch a TRUNCATE based on this:

"... It has the same effect as an unqualified DELETE on each table, ..."

from here:

http://www.postgresql.org/docs/9.4/interactive/sql-truncate.html

It was then explained that while TRUNCATE had the same end result as
'DELETE FROM some_table' it was actually a separate command and action.
Tim wants to catch a TRUNCATE and turn it into an ignore.


--
Adrian Klaver
adrian.klaver@aklaver.com

On Thu, Jul 23, 2015 at 12:09 PM, Adrian Klaver
<adrian.klaver@aklaver.com> wrote:
> On 07/23/2015 04:57 AM, Tim Smith wrote:
>>
>> Andrew,
>>
>>  From the manual:
>>
>> It is important to realize that a rule is really a command
>> transformation mechanism, or command macro. The transformation happens
>> before the execution of the command starts. If you actually want an
>> operation that fires independently for each physical row, you probably
>> want to use a trigger, not a rule
>>
>>
>> Thus, I should not have to use a trigger for TRUNCATE because the "each
>> row" concept does not apply.     Plus it makes perfect sense to want to
>> transform the truncate command and transform into ignore
>>
>
> Just in case it has not been made obvious yet, rules are silently
> deprecated. They still exist because views depend on them, but it is
> generally considered best practices to not use them outside that realm. So
> if you want the rule behavior to change for TRUNCATE(if that is even
> possible) you are fighting an uphill battle. You may pursue that fight of
> course, but I would think you will get a quicker return on your time if you
> just forget about using a RULE and stick to a TRIGGER instead.
>


Also OP needs to know that COPY commands are ignored by rules as well.
I agree, stick to triggers, they're faster and less error prone.

On 07/23/2015 11:15 AM, Rob Sargent wrote:

On 07/23/2015 12:09 PM, Adrian Klaver wrote:

On 07/23/2015 04:57 AM, Tim Smith wrote:

Andrew,

 From the manual:

It is important to realize that a rule is really a command
transformation mechanism, or command macro. The transformation happens
before the execution of the command starts. If you actually want an
operation that fires independently for each physical row, you probably
want to use a trigger, not a rule


Thus, I should not have to use a trigger for TRUNCATE because the "each
row" concept does not apply.     Plus it makes perfect sense to want to
transform the truncate command and transform into ignore

Just in case it has not been made obvious yet, rules are silently
deprecated. They still exist because views depend on them, but it is
generally considered best practices to not use them outside that
realm. So if you want the rule behavior to change for TRUNCATE(if that
is even possible) you are fighting an uphill battle. You may pursue
that fight of course, but I would think you will get a quicker return
on your time if you just forget about using a RULE and stick to a
TRIGGER instead.

Or change to using delete instead of truncate?

Well Tim has an ON DELETE rule:

http://www.postgresql.org/message-id/CA+HuS5G2bZYYOGTJrw+VosjUPO298swxuU=JOrFAv54UT7vniQ@mail.gmail.com

His expectation was that would also catch a TRUNCATE based on this:

"... It has the same effect as an unqualified DELETE on each table, ..."

from here:

http://www.postgresql.org/docs/9.4/interactive/sql-truncate.html

It was then explained that while TRUNCATE had the same end result as 'DELETE FROM some_table' it was actually a separate command and action. Tim wants to catch a TRUNCATE and turn it into an ignore.

On Thu, Jul 23, 2015 at 12:28:32PM -0600, Rob Sargent wrote:

> I'm suggesting OP might find changing truncate statements to deletes
> (without a where clause) a simpler solution. Something has to change.

Well, OP isn't looking for a solution to "delete all rows"
but rather to _prevent_ deletion.

Tim can't go forth and tell Blackhats to "please use DELETE
rather than TRUNCATE", right ?

AFAICT it'd be more useful to advise OP to revoke TRUNCATE
rights on tables.

Karsten
--
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E167 67FD A291 2BEA 73BD  4537 78B9 A9F9 E407 1346

On Thu, Jul 23, 2015 at 12:28:32PM -0600, Rob Sargent wrote:

I'm suggesting OP might find changing truncate statements to deletes
(without a where clause) a simpler solution. Something has to change.

Well, OP isn't looking for a solution to "delete all rows"
but rather to _prevent_ deletion.

Tim can't go forth and tell Blackhats to "please use DELETE
rather than TRUNCATE", right ?

AFAICT it'd be more useful to advise OP to revoke TRUNCATE
rights on tables.

Karsten

On 07/23/2015 05:08 PM, Rob Sargent wrote:
> On 07/23/2015 04:15 PM, Karsten Hilbert wrote:
>> On Thu, Jul 23, 2015 at 12:28:32PM -0600, Rob Sargent wrote:
>>
>>> I'm suggesting OP might find changing truncate statements to deletes
>>> (without a where clause) a simpler solution. Something has to change.
>> Well, OP isn't looking for a solution to "delete all rows"
>> but rather to _prevent_ deletion.
>>
>> Tim can't go forth and tell Blackhats to "please use DELETE
>> rather than TRUNCATE", right ?
>>
>> AFAICT it'd be more useful to advise OP to revoke TRUNCATE
>> rights on tables.
>>
>> Karsten
> Not sure about Tim and the Blackhats (there's a band name in there
> somewhere) but Wouldn't OP have exact same code to fix, one way or another?
>

I think the point was, the OP(Tim) might not have access to the code
that is trying to TRUNCATE. This could be because it is coming from
authorized users who are writing their own code or unauthorized
users(Blackhats) who are trying to sneak code in.


--
Adrian Klaver
adrian.klaver@aklaver.com

On 07/23/2015 05:08 PM, Rob Sargent wrote:

On 07/23/2015 04:15 PM, Karsten Hilbert wrote:

On Thu, Jul 23, 2015 at 12:28:32PM -0600, Rob Sargent wrote:

I'm suggesting OP might find changing truncate statements to deletes
(without a where clause) a simpler solution. Something has to change.

Well, OP isn't looking for a solution to "delete all rows"
but rather to _prevent_ deletion.

Tim can't go forth and tell Blackhats to "please use DELETE
rather than TRUNCATE", right ?

AFAICT it'd be more useful to advise OP to revoke TRUNCATE
rights on tables.

Karsten

Not sure about Tim and the Blackhats (there's a band name in there
somewhere) but Wouldn't OP have exact same code to fix, one way or another?

I think the point was, the OP(Tim) might not have access to the code that is trying to TRUNCATE. This could be because it is coming from authorized users who are writing their own code or unauthorized users(Blackhats) who are trying to sneak code in.

On 07/23/2015 05:37 PM, Rob Sargent wrote:
> On 07/23/2015 06:27 PM, Adrian Klaver wrote:
>> On 07/23/2015 05:08 PM, Rob Sargent wrote:
>>> On 07/23/2015 04:15 PM, Karsten Hilbert wrote:
>>>> On Thu, Jul 23, 2015 at 12:28:32PM -0600, Rob Sargent wrote:
>>>>
>>>>> I'm suggesting OP might find changing truncate statements to deletes
>>>>> (without a where clause) a simpler solution. Something has to change.
>>>> Well, OP isn't looking for a solution to "delete all rows"
>>>> but rather to _prevent_ deletion.
>>>>
>>>> Tim can't go forth and tell Blackhats to "please use DELETE
>>>> rather than TRUNCATE", right ?
>>>>
>>>> AFAICT it'd be more useful to advise OP to revoke TRUNCATE
>>>> rights on tables.
>>>>
>>>> Karsten
>>> Not sure about Tim and the Blackhats (there's a band name in there
>>> somewhere) but Wouldn't OP have exact same code to fix, one way or
>>> another?
>>>
>>
>> I think the point was, the OP(Tim) might not have access to the code
>> that is trying to TRUNCATE. This could be because it is coming from
>> authorized users who are writing their own code or unauthorized
>> users(Blackhats) who are trying to sneak code in.
>>
>>
> Fair enough but both blackhats and the authorized are just as likely to
> drop the database as truncate something (intentionally or not) and
> backups stashed everywhere is the first order of business.

Well that is a different crisis and not covered by rules or triggers:)


--
Adrian Klaver
adrian.klaver@aklaver.com

On 24 July 2015 at 01:37, Rob Sargent <robjsargent@gmail.com> wrote:

> Fair enough but both blackhats and the authorized are just as likely to drop
> the database as truncate something (intentionally or not) and backups
> stashed everywhere is the first order of business.


That's not the point.  Backups are important, but so is the concept of
various layers of anti-fat-finger protection.   Restoring off backups
should be last resort, not first.

On 2015-07-24 10:29:21 +0100, Tim Smith wrote:
> That's not the point.  Backups are important, but so is the concept of
> various layers of anti-fat-finger protection.   Restoring off backups
> should be last resort, not first.

Oh, comeon. Install a TRUNCATE trigger and let this thread die.

Andres

On Fri, Jul 24, 2015 at 10:24:55AM +0100, Tim Smith wrote:
>
> If that's how the developers feel about rules, i.e they can't be
> bothered to make any changes to the rules code any more, no matter how
> minor (e.g. this TRUNCATE issue)

Who is this "they"?  As I think I suggested in another mail, if you
think this is trivial and easy then I think you should propose the
patch to solve it.  I understand what you're saying; I think the
solution is self-evident (add a statement trigger that captures
TRUNCATE and DO INSTEAD NOTHING), so I just wouldn't be bothered to
fix this.  But I suspect things are the way they are partly because
nobody proposed or implemented a patch for this behaviour before.

The manual is also quite clear in what statements you can
write rules about; by implication, other statements are not covered,
so I'm not actually sure why you think the manual is misleading.

Best regards,

A
--
Andrew Sullivan
ajs@crankycanuck.ca

On 07/24/2015 02:24 AM, Tim Smith wrote:
>>
>> Just in case it has not been made obvious yet, rules are silently
>> deprecated. They still exist because views depend on them, but it is
>> generally considered best practices to not use them outside that realm.
>
>
> Well, the manual doesn't seem to reflect that fact.
>
> If that's how the developers feel about rules, i.e they can't be
> bothered to make any changes to the rules code any more, no matter how
> minor (e.g. this TRUNCATE issue), then you should explicitly state in
> the manual that they are depreciated, and stop making stupid
> statements like "so if many rows are affected in one statement, a rule
> issuing one extra command is likely to be faster than a trigger" that
> encourage people to use rules !
>

Seems that section needs editing to make it clearer that this depends on
what type of trigger you use. Or as it states here:

http://www.postgresql.org/docs/9.4/interactive/sql-createtrigger.html
"
A trigger that is marked FOR EACH ROW is called once for every row that
the operation modifies. For example, a DELETE that affects 10 rows will
cause any ON DELETE triggers on the target relation to be called 10
separate times, once for each deleted row. In contrast, a trigger that
is marked FOR EACH STATEMENT only executes once for any given operation,
regardless of how many rows it modifies (in particular, an operation
that modifies zero rows will still result in the execution of any
applicable FOR EACH STATEMENT triggers).
"

At any rate you know what the situation is. Getting increasingly
belligerent is not going to help that situation and the energy would
seem to me better spent on adapting to reality and moving on.

--
Adrian Klaver
adrian.klaver@aklaver.com

On Fri, Jul 24, 2015 at 3:27 AM, Tim Smith <randomdev4@gmail.com> wrote:
> On 23 July 2015 at 19:25, Scott Marlowe <scott.marlowe@gmail.com> wrote:
>> stick to triggers, they're faster
>
>
> Erm, not according to your beloved manual !!!
>
> 38.7. Rules Versus Triggers
>
> " a rule issuing one extra command is likely to be faster than a trigger"
> "The summary is, rules will only be significantly slower than triggers
> if their actions result in large and badly qualified joins, a
> situation where the planner fails."

So, that's the sum total of what you took away from my post?
Nevermind, I'll leave you alone.

On 07/24/2015 02:32 AM, Andres Freund wrote:
>
> On 2015-07-24 10:29:21 +0100, Tim Smith wrote:
>> That's not the point.  Backups are important, but so is the concept of
>> various layers of anti-fat-finger protection.   Restoring off backups
>> should be last resort, not first.
>
> Oh, comeon. Install a TRUNCATE trigger and let this thread die.
>
> Andres
>

Please god, +1.

JD


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Announcing "I'm offended" is basically telling the world you can't
control your own emotions, so everyone else should do it for you.

>
> Just in case it has not been made obvious yet, rules are silently
> deprecated. They still exist because views depend on them, but it is
> generally considered best practices to not use them outside that realm.


Well, the manual doesn't seem to reflect that fact.

If that's how the developers feel about rules, i.e they can't be
bothered to make any changes to the rules code any more, no matter how
minor (e.g. this TRUNCATE issue), then you should explicitly state in
the manual that they are depreciated, and stop making stupid
statements like "so if many rows are affected in one statement, a rule
issuing one extra command is likely to be faster than a trigger" that
encourage people to use rules !

On 23 July 2015 at 19:25, Scott Marlowe <scott.marlowe@gmail.com> wrote:
> stick to triggers, they're faster


Erm, not according to your beloved manual !!!

38.7. Rules Versus Triggers

" a rule issuing one extra command is likely to be faster than a trigger"
"The summary is, rules will only be significantly slower than triggers
if their actions result in large and badly qualified joins, a
situation where the planner fails."