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Improve documentation for default_tablespace on partitioned tables
- adbcd3e6634a 12.7 landed
- 94b9cb722552 14.0 landed
- 896cedc7d578 13.3 landed
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Fix tablespace inheritance for partitioned rels
- 87259588d0ab 12.0 cited
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default_tablespace doc and partitioned rels
Justin Pryzby <pryzby@telsasoft.com> — 2021-04-16T14:31:35Z
commit 87259588d0ab0b8e742e30596afa7ae25caadb18 Author: Alvaro Herrera <alvherre@alvh.no-ip.org> Date: Thu Apr 25 10:20:23 2019 -0400 Fix tablespace inheritance for partitioned rels This doc change doesn't make sense to me: +++ b/doc/src/sgml/config.sgml @@ -7356,7 +7356,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; <para> This variable specifies the default tablespace in which to create objects (tables and indexes) when a <command>CREATE</command> command does - not explicitly specify a tablespace. + not explicitly specify a tablespace. It also determines the tablespace + that a partitioned relation will direct future partitions to. </para> default_tablespace is a global GUC, so if a partitioned relation "directs" partitions anywhere, it's not to the fallback value of the GUC, but to its reltablespace, as this patch wrote in doc/src/sgml/ref/create_table.sgml: + the tablespace specified overrides <literal>default_tablespace</literal> + as the default tablespace to use for any newly created partitions when no + other tablespace is explicitly specified. Maybe I'm misreading config.sgml somehow ? I thought it would be more like this (but actually I think <default_tablespace> shouldn't say anything at all): + ... It also determines the tablespace where new partitions are created, + if the parent, partitioned relation doesn't have a tablespace set. -- Justin -
Re: default_tablespace doc and partitioned rels
Alvaro Herrera <alvherre@alvh.no-ip.org> — 2021-04-16T20:19:18Z
On 2021-Apr-16, Justin Pryzby wrote: > +++ b/doc/src/sgml/config.sgml > @@ -7356,7 +7356,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; > <para> > This variable specifies the default tablespace in which to create > objects (tables and indexes) when a <command>CREATE</command> command does > - not explicitly specify a tablespace. > + not explicitly specify a tablespace. It also determines the tablespace > + that a partitioned relation will direct future partitions to. > </para> > > default_tablespace is a global GUC, so if a partitioned relation "directs" > partitions anywhere, it's not to the fallback value of the GUC, but to its > reltablespace, as this patch wrote in doc/src/sgml/ref/create_table.sgml: Yes, but also the partitioned table's reltablespace is going to be set to default_tablespace, if no tablespace is explicitly specified in the partitioned table creation. A partitioned table is not created anywhere itself; the only thing it can do, is direct where are future partitions created. I don't think it's 100% obvious that default_tablespace will become the partitioned table's tablespace, which is why I added that phrase. I understand that the language might be unclear, but I don't think either of your suggestions make this any clearer. Removing it just hides the behavior, and this one: > + ... It also determines the tablespace where new partitions are created, > + if the parent, partitioned relation doesn't have a tablespace set. just documents that default_tablespace will be in effect at partition CREATE time, but it fails to remind the user that the partitioned table will acquire default_tablespace as its own tablespace. Maybe we can reword it in some other way. "If this parameter is set when a partitioned table is created, it will become the default tablespace for future partitions too, even if default_tablespace itself is reset later" ...?? -- Álvaro Herrera 39°49'30"S 73°17'W "En las profundidades de nuestro inconsciente hay una obsesiva necesidad de un universo lógico y coherente. Pero el universo real se halla siempre un paso más allá de la lógica" (Irulan)
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Re: default_tablespace doc and partitioned rels
Justin Pryzby <pryzby@telsasoft.com> — 2021-04-16T21:02:01Z
On Fri, Apr 16, 2021 at 04:19:18PM -0400, Alvaro Herrera wrote: > Maybe we can reword it in some other way. "If this parameter is set > when a partitioned table is created, it will become the default > tablespace for future partitions too, even if default_tablespace itself > is reset later" ...?? +1 I'd say: If this parameter is set when a partitioned table is created, the partitioned table's tablespace will be set to the given tablespace, and which will be the default tablespace for partitions create in the future, even if default_tablespace itself has since been changed. -- Justin
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Re: default_tablespace doc and partitioned rels
Alvaro Herrera <alvherre@alvh.no-ip.org> — 2021-04-29T15:39:11Z
On 2021-Apr-16, Justin Pryzby wrote: > If this parameter is set when a partitioned table is created, the partitioned > table's tablespace will be set to the given tablespace, and which will be the > default tablespace for partitions create in the future, even if > default_tablespace itself has since been changed. Pushed with very similar wording: + <para> + If this parameter is set to a value other than the empty string + when a partitioned table is created, the partitioned table's + tablespace will be set to that value, which will be used as + the default tablespace for partitions created in the future, + even if <varname>default_tablespace</varname> has changed since then. + </para> I made it a separate paragraph at the end, because I noticed that I had added the note in an inappropriate place in the earlier commit; the second paragraph in particular is more general than this one. Also looking at that one I realized that we need to talk about the value being "not the empty string". I hope it's clear enough now, but if you or anybody have further suggestion on improving this, I'm listening. Thanks -- Álvaro Herrera Valdivia, Chile "If you have nothing to say, maybe you need just the right tool to help you not say it." (New York Times, about Microsoft PowerPoint)