Thread: Trigger behaviour not as stated
The following documentation comment has been logged on the website: Page: https://www.postgresql.org/docs/10/static/sql-createtrigger.html Description: URL: https://www.postgresql.org/docs/current/static/sql-createtrigger.html Statement: "In contrast, row-level triggers are fired for all affected partitions or child tables." Row-level triggers are not fired on child tables where the trigger ON BEFORE UPDATE | DELETE is on the parent table. Only works on BEFORE INSERT.
On Wed, Nov 29, 2017 at 07:39:34PM +0000, ian@thepathcentral.com wrote: > The following documentation comment has been logged on the website: > > Page: https://www.postgresql.org/docs/10/static/sql-createtrigger.html > Description: > > URL: https://www.postgresql.org/docs/current/static/sql-createtrigger.html > > Statement: "In contrast, row-level triggers are fired for all affected > partitions or child tables." > > Row-level triggers are not fired on child tables where the trigger ON BEFORE > UPDATE | DELETE is on the parent table. Only works on BEFORE INSERT. Uh, can you email us an example of the failure so we can research it? Thanks. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
On Wed, Jan 24, 2018 at 01:10:08PM -0500, Bruce Momjian wrote: > On Wed, Nov 29, 2017 at 07:39:34PM +0000, ian@thepathcentral.com wrote: > > The following documentation comment has been logged on the website: > > > > Page: https://www.postgresql.org/docs/10/static/sql-createtrigger.html > > Description: > > > > URL: https://www.postgresql.org/docs/current/static/sql-createtrigger.html > > > > Statement: "In contrast, row-level triggers are fired for all affected > > partitions or child tables." > > > > Row-level triggers are not fired on child tables where the trigger ON BEFORE > > UPDATE | DELETE is on the parent table. Only works on BEFORE INSERT. > > Uh, can you email us an example of the failure so we can research it? > Thanks. OK, I have some more details on this. First there is the Stackoverflow report: https://stackoverflow.com/questions/47557665/postgresql-on-before-delete-trigger-not-firing-on-a-parent-table-in-an-inheritan The report confirms that row-level triggers are fired _only_ on affected tables (meaning the table that had a row change), not on any table mentioned _or_ affected. The current wording, added in this commit: commit 501ed02cf6f4f60c3357775eb07578aebc912d3a Author: Andrew Gierth <rhodiumtoad@postgresql.org> Date: Wed Jun 28 18:55:03 2017 +0100 Fix transition tables for partition/inheritance. We disallow row-level triggers with transition tables on child tables. Transition tables for triggers on the parent table contain only those columns present in the parent. (We can't mix tuple formats in a single transition table.) Patch by Thomas Munro Discussion: https://postgr.es/m/CA%2BTgmoZzTBBAsEUh4MazAN7ga%3D8SsMC-Knp-6cetts9yNZUCcg%40mail.gmail.com should be improved. The attached patch updates the docs to say statement-level triggers fire on the "referenced" table, while row-level triggers fire only on the "affected" table, (vs. all affected tables) even if they are not referenced in the query. I would backpatch this to PG 10. The second attachment is an SQL query script that illustrates the behavior. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
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On Thu, Jan 25, 2018 at 11:07 AM, Bruce Momjian <bruce@momjian.us> wrote: > On Wed, Jan 24, 2018 at 01:10:08PM -0500, Bruce Momjian wrote: >> On Wed, Nov 29, 2017 at 07:39:34PM +0000, ian@thepathcentral.com wrote: >> > The following documentation comment has been logged on the website: >> > >> > Page: https://www.postgresql.org/docs/10/static/sql-createtrigger.html >> > Description: >> > >> > URL: https://www.postgresql.org/docs/current/static/sql-createtrigger.html >> > >> > Statement: "In contrast, row-level triggers are fired for all affected >> > partitions or child tables." >> > >> > Row-level triggers are not fired on child tables where the trigger ON BEFORE >> > UPDATE | DELETE is on the parent table. Only works on BEFORE INSERT. > > OK, I have some more details on this. First there is the Stackoverflow > report: > > https://stackoverflow.com/questions/47557665/postgresql-on-before-delete-trigger-not-firing-on-a-parent-table-in-an-inheritan > > The report confirms that row-level triggers are fired _only_ on affected > tables (meaning the table that had a row change), not on any table > mentioned _or_ affected. The current wording, added in this commit: > > commit 501ed02cf6f4f60c3357775eb07578aebc912d3a > Author: Andrew Gierth <rhodiumtoad@postgresql.org> > Date: Wed Jun 28 18:55:03 2017 +0100 > > Fix transition tables for partition/inheritance. > > We disallow row-level triggers with transition tables on child tables. > Transition tables for triggers on the parent table contain only those > columns present in the parent. (We can't mix tuple formats in a > single transition table.) > > Patch by Thomas Munro > > Discussion: https://postgr.es/m/CA%2BTgmoZzTBBAsEUh4MazAN7ga%3D8SsMC-Knp-6cetts9yNZUCcg%40mail.gmail.com > > should be improved. The attached patch updates the docs to say > statement-level triggers fire on the "referenced" table, while row-level > triggers fire only on the "affected" table, (vs. all affected tables) > even if they are not referenced in the query. I would backpatch this to > PG 10. +1 I was trying to convey that, but it does seem a little terse and cryptic. Your addition of "referenced" and "only" make it clearer. -- Thomas Munro http://www.enterprisedb.com
Thomas Munro <thomas.munro@enterprisedb.com> writes:
> On Thu, Jan 25, 2018 at 11:07 AM, Bruce Momjian <bruce@momjian.us> wrote:
>> ... The attached patch updates the docs to say
>> statement-level triggers fire on the "referenced" table, while row-level
>> triggers fire only on the "affected" table, (vs. all affected tables)
>> even if they are not referenced in the query. I would backpatch this to
>> PG 10.
> I was trying to convey that, but it does seem a little terse and
> cryptic. Your addition of "referenced" and "only" make it clearer.
Hm, the first part of Bruce's change seems fine, but I think this wording:
... In contrast,
! row-level triggers are fired only on affected partitions or child tables,
! even if they are not referenced in the query.
is still confusing. How about something like
In contrast, row-level triggers are fired for each actual row change,
including changes in partitions or child tables that are not directly
named in the query.
Possibly "row operation" would be better than "row change".
regards, tom lane
On Sun, Jan 28, 2018 at 02:18:38PM -0500, Tom Lane wrote: > Thomas Munro <thomas.munro@enterprisedb.com> writes: > > On Thu, Jan 25, 2018 at 11:07 AM, Bruce Momjian <bruce@momjian.us> wrote: > >> ... The attached patch updates the docs to say > >> statement-level triggers fire on the "referenced" table, while row-level > >> triggers fire only on the "affected" table, (vs. all affected tables) > >> even if they are not referenced in the query. I would backpatch this to > >> PG 10. > > > I was trying to convey that, but it does seem a little terse and > > cryptic. Your addition of "referenced" and "only" make it clearer. > > Hm, the first part of Bruce's change seems fine, but I think this wording: > > ... In contrast, > ! row-level triggers are fired only on affected partitions or child tables, > ! even if they are not referenced in the query. > > is still confusing. How about something like > > In contrast, row-level triggers are fired for each actual row change, > including changes in partitions or child tables that are not directly > named in the query. > > Possibly "row operation" would be better than "row change". Uh, I don't think we want to highlight the statement vs row difference here but the fact that statement triggers fire on the referenced object and not on the effected rows. I have attached an updated patch which I think is an improvement. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
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Bruce Momjian <bruce@momjian.us> writes:
> Uh, I don't think we want to highlight the statement vs row difference
> here but the fact that statement triggers fire on the referenced object
> and not on the effected rows. I have attached an updated patch which I
> think is an improvement
statement-level triggers for its partitions or child tables. In contrast,
! row-level triggers are fired on the rows in effected partitions or
! child tables, even if they are not referenced in the query.
I still think that that's not well written. A large part of the confusion
here is over what "referenced" means. To my mind, child tables/partitions
are referenced by an inherited query, just not explicitly. So that's why
I'd prefer wording like "directly named in the query" (or "explicitly
named"). If you insist on using "referenced" you could write "explicitly
referenced", but IMO that's longer and no clearer.
A lesser complaint is that this reads like the antecedent of "they" is the
rows, not the tables containing them, making the meaning of "referenced"
even less clear.
Maybe something like
In contrast, row-level triggers are fired for individual row change
events, and the triggers that are fired for an event are those
attached to the specific table containing the changed row, even if
it is a partition or child table not directly named in the query.
regards, tom lane
On Sun, Jan 28, 2018 at 03:57:07PM -0500, Tom Lane wrote: > Bruce Momjian <bruce@momjian.us> writes: > > Uh, I don't think we want to highlight the statement vs row difference > > here but the fact that statement triggers fire on the referenced object > > and not on the effected rows. I have attached an updated patch which I > > think is an improvement > > statement-level triggers for its partitions or child tables. In contrast, > ! row-level triggers are fired on the rows in effected partitions or > ! child tables, even if they are not referenced in the query. > > I still think that that's not well written. A large part of the confusion > here is over what "referenced" means. To my mind, child tables/partitions > are referenced by an inherited query, just not explicitly. So that's why > I'd prefer wording like "directly named in the query" (or "explicitly > named"). If you insist on using "referenced" you could write "explicitly > referenced", but IMO that's longer and no clearer. > > A lesser complaint is that this reads like the antecedent of "they" is the > rows, not the tables containing them, making the meaning of "referenced" > even less clear. > > Maybe something like > > In contrast, row-level triggers are fired for individual row change > events, and the triggers that are fired for an event are those > attached to the specific table containing the changed row, even if > it is a partition or child table not directly named in the query. Oh, I am sorry. I was focused on the first part of the sentence and didn't notice your change to the second part. How is this attachment? -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
Attachment
Bruce Momjian <bruce@momjian.us> writes:
> Oh, I am sorry. I was focused on the first part of the sentence and
> didn't notice your change to the second part. How is this attachment?
Seems same as your previous version?
regards, tom lane
On Sun, Jan 28, 2018 at 06:12:01PM -0500, Tom Lane wrote: > Bruce Momjian <bruce@momjian.us> writes: > > Oh, I am sorry. I was focused on the first part of the sentence and > > didn't notice your change to the second part. How is this attachment? > > Seems same as your previous version? OK, new vesion that uses "explicitly named" in both modified doc lines. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
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The original confusion on this is answered in part by the following statement (taken from the answer to my SO question):
"UPDATEs and DELETEs on the parent table will affect rows in the child tables (if you don't specify ONLY), but triggers will only be fired by data modifications directed directly against the table with the trigger on it "This clearly explains that a trigger attached to a parent table will not fire if the data being modified is in a child table.
The second part of the confusion is that INSERT is not considered to be a row modification and will fire a BEFORE INSERT trigger on the parent table even when the data goes into a child (whereas UPDATE and DELETE will not fire a parent trigger).
My proposal (adapted from Tom's):
In contrast, row-level UPDATE and DELETE triggers are fired for individual row change
events only on the table to which the trigger is attached. Therefore, UPDATE and DELETE triggers on
events only on the table to which the trigger is attached. Therefore, UPDATE and DELETE triggers on
a parent table will only fire when rows in the parent table are being modified. Likewise,
UPDATE and DELETE triggers on a child table will only fire when rows in the child table are being modified.
Note that INSERT statements do not follow these update rules, so statements run on parent tables will
insert rows in child tables if the trigger function so directs.
The last line may need a bit of work, but I feel the text above it is clear.
Ian
On Mon, 29 Jan 2018 at 07:17 Bruce Momjian <bruce@momjian.us> wrote:
On Sun, Jan 28, 2018 at 06:12:01PM -0500, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > Oh, I am sorry. I was focused on the first part of the sentence and
> > didn't notice your change to the second part. How is this attachment?
>
> Seems same as your previous version?
OK, new vesion that uses "explicitly named" in both modified doc lines.
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
On Mon, Jan 29, 2018 at 11:32:34AM +0000, Ian R. Campbell wrote:
> The second part of the confusion is that INSERT is not considered to be a row
> modification and will fire a BEFORE INSERT trigger on the parent table even
> when the data goes into a child (whereas UPDATE and DELETE will not fire a
> parent trigger).
Ian, that is not true based on my testing. Running that attached script
that I already posted shows:
test=> INSERT INTO parent VALUES (1, 'one');
NOTICE: Called by parent INSERT
INSERT 0 1
test=> INSERT INTO child VALUES (2, 'two');
--> NOTICE: Called by child INSERT
INSERT 0 1
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
+ Ancient Roman grave inscription +
Attachment
On Sun, Jan 28, 2018 at 06:17:19PM -0500, Bruce Momjian wrote: > On Sun, Jan 28, 2018 at 06:12:01PM -0500, Tom Lane wrote: > > Bruce Momjian <bruce@momjian.us> writes: > > > Oh, I am sorry. I was focused on the first part of the sentence and > > > didn't notice your change to the second part. How is this attachment? > > > > Seems same as your previous version? > > OK, new vesion that uses "explicitly named" in both modified doc lines. Applied and backpatched through 10, where the text was added. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +