Обсуждение: Re: Indexes mysteriously change to ON ONLY

Rumpi Gravenstein <rgravens@gmail.com> writes:
>> We have recently discovered that on some of our partitioned tables indexes
>> that were created as:
>> 
>> CREATE UNIQUE INDEX chapter_u01 USING btree (dur_uk, catalog_id)
>> 
>> somehow changed to include the ON ONLY option:
>> 
>> CREATE UNIQUE INDEX chapter_u01 *ON ONLY *chapter USING btree (dur_uk,
>> catalog_id)

What do you mean "somehow changed"?  There is nothing in the system
catalogs that stores that exact string, so I suppose what you mean
is that some tool is presenting the indexes to you that way.

If that tool is pg_dump, this is its normal behavior.  There will
be other commands in its output that build the rest of the
partitioned index set.

            regards, tom lane

> On Jan 27, 2023, at 13:01, Rumpi Gravenstein <rgravens@gmail.com> wrote:
>
> We are using the pg_indexes view (indexdef) to retrieve the index definition.

This is as expected.  Once the index is created on the partitioned set of tables, the index on the *root* table will be
ONONLY that table; the child tables appear separately: 

xof=# create table t (i bigint) partition by range(i);
CREATE TABLE
xof=# create table t001 partition of t for values from (1) to (2);
CREATE TABLE
xof=# create index on t(i);
CREATE INDEX
xof=# select * from pg_indexes where tablename = 't';
 schemaname | tablename | indexname | tablespace |                       indexdef
------------+-----------+-----------+------------+-------------------------------------------------------
 public     | t         | t_i_idx   |            | CREATE INDEX t_i_idx ON ONLY public.t USING btree (i)
(1 row)

xof=# select * from pg_indexes where tablename = 't001';
 schemaname | tablename | indexname  | tablespace |                        indexdef
------------+-----------+------------+------------+--------------------------------------------------------
 public     | t001      | t001_i_idx |            | CREATE INDEX t001_i_idx ON public.t001 USING btree (i)
(1 row)

Rumpi Gravenstein <rgravens@gmail.com> writes:
> We are using the pg_indexes view (indexdef) to retrieve the index
> definition.

Ah.

> Are you saying that as a normal part of building an index, there are short
> periods of time where the pg_indexes view will show the index with ON ONLY
> specified?

No, there's no "short periods", this is what it shows.  That's partly
because the output is designed for pg_dump to use.  But there's
a reasonably good argument for it anyway, which is that if you just
say "create index" then that's effectively a macro for building the
whole partitioned index set.  That pg_indexes entry is only about the
top-level "virtual" index, and there are other entries for the leaf
indexes.  For example,

regression=# create table foo (f1 int primary key) partition by list (f1);
CREATE TABLE
regression=# create table foo_1 partition of foo for values in (1);
CREATE TABLE
regression=# create table foo_2 partition of foo for values in (2);
CREATE TABLE
regression=# select tablename,indexname,indexdef from pg_indexes where indexname like 'foo%';
 tablename | indexname  |                             indexdef
-----------+------------+------------------------------------------------------------------
 foo       | foo_pkey   | CREATE UNIQUE INDEX foo_pkey ON ONLY public.foo USING btree (f1)
 foo_1     | foo_1_pkey | CREATE UNIQUE INDEX foo_1_pkey ON public.foo_1 USING btree (f1)
 foo_2     | foo_2_pkey | CREATE UNIQUE INDEX foo_2_pkey ON public.foo_2 USING btree (f1)
(3 rows)

If you wanted to reconstruct this from individual parts, as pg_dump does,
you'd issue those commands and then connect them together with ATTACH
PARTITION commands.

            regards, tom lane

Tom/Christophe  I now understand.  Thanks for the clear explanation.

On Fri, Jan 27, 2023 at 4:16 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

Rumpi Gravenstein <rgravens@gmail.com> writes:
> We are using the pg_indexes view (indexdef) to retrieve the index
> definition.

Ah.

> Are you saying that as a normal part of building an index, there are short
> periods of time where the pg_indexes view will show the index with ON ONLY
> specified?

No, there's no "short periods", this is what it shows.  That's partly
because the output is designed for pg_dump to use.  But there's
a reasonably good argument for it anyway, which is that if you just
say "create index" then that's effectively a macro for building the
whole partitioned index set.  That pg_indexes entry is only about the
top-level "virtual" index, and there are other entries for the leaf
indexes.  For example,

regression=# create table foo (f1 int primary key) partition by list (f1);
CREATE TABLE
regression=# create table foo_1 partition of foo for values in (1);
CREATE TABLE
regression=# create table foo_2 partition of foo for values in (2);
CREATE TABLE
regression=# select tablename,indexname,indexdef from pg_indexes where indexname like 'foo%';
 tablename | indexname  |                             indexdef                             
-----------+------------+------------------------------------------------------------------
 foo       | foo_pkey   | CREATE UNIQUE INDEX foo_pkey ON ONLY public.foo USING btree (f1)
 foo_1     | foo_1_pkey | CREATE UNIQUE INDEX foo_1_pkey ON public.foo_1 USING btree (f1)
 foo_2     | foo_2_pkey | CREATE UNIQUE INDEX foo_2_pkey ON public.foo_2 USING btree (f1)
(3 rows)

If you wanted to reconstruct this from individual parts, as pg_dump does,
you'd issue those commands and then connect them together with ATTACH
PARTITION commands.

                        regards, tom lane

--

Rumpi Gravenstein