mirror of
https://github.com/postgres/postgres.git
synced 2025-06-02 00:01:40 -04:00
787514b30b
custom_query_jumble (introduced in 5ac462e2b7ac as a node field
attribute) is now assigned to the expanded reference name "eref" of
RangeTblEntry, adding in the query jumble computation the non-qualified
aliased relation name, without the list of column names. The relation
OID is removed from the query jumbling.
The effects of this change can be seen in the tests added by
3430215fe35f, where pg_stat_statements (PGSS) entries are now grouped
using the relation name, ignoring the relation search_path may point at.
For example, these two relations are different, but are now grouped in a
single PGSS entry as they are assigned the same query ID:
CREATE TABLE foo1.tab (a int);
CREATE TABLE foo2.tab (b int);
SET search_path = 'foo1';
SELECT count(*) FROM tab;
SET search_path = 'foo2';
SELECT count(*) FROM tab;
SELECT count(*) FROM foo1.tab;
SELECT count(*) FROM foo2.tab;
SELECT query, calls FROM pg_stat_statements WHERE query ~ 'FROM tab';
query | calls
--------------------------+-------
SELECT count(*) FROM tab | 4
(1 row)
It is still possible to use an alias in the FROM clause to split these.
This behavior is useful for relations re-created with the same name,
where queries based on such relations would be grouped in the same
PGSS entry. For permanent schemas, it should not really matter in
practice. The main benefit is for workloads that use a lot of temporary
relations, which are usually re-created with the same name continuously.
These can be a heavy source of bloat in PGSS depending on the workload.
Such entries can now be grouped together, improving the user experience.
The original idea from Christoph Berg used catalog lookups to find
temporary relations, something that the query jumble has never done, and
it could cause some performance regressions. The idea to use
RangeTblEntry.eref and the relation name, applying the same rules for
all relations, temporary and not temporary, has been proposed by Tom
Lane. The documentation additions have been suggested by Sami Imseih.
Author: Michael Paquier <michael@paquier.xyz>
Co-authored-by: Sami Imseih <samimseih@gmail.com>
Reviewed-by: Christoph Berg <myon@debian.org>
Reviewed-by: Lukas Fittl <lukas@fittl.com>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/Z9iWXKGwkm8RAC93@msg.df7cb.de
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.