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* [PATCH v27 5/5] Doc: Add Collation Versions section.
@ 2020-03-11 02:01 Thomas Munro <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Thomas Munro @ 2020-03-11 02:01 UTC (permalink / raw)
Supply a brief introduction to collation version concepts.
Author: Thomas Munro <[email protected]>
Reviewed-by: Julien Rouhaud <[email protected]>
Discussion: https://postgr.es/m/CAEepm%3D0uEQCpfq_%2BLYFBdArCe4Ot98t1aR4eYiYTe%3DyavQygiQ%40mail.gmail.com
---
doc/src/sgml/charset.sgml | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/doc/src/sgml/charset.sgml b/doc/src/sgml/charset.sgml
index 4b4563c5b9..12a82ff18c 100644
--- a/doc/src/sgml/charset.sgml
+++ b/doc/src/sgml/charset.sgml
@@ -948,6 +948,41 @@ CREATE COLLATION ignore_accents (provider = icu, locale = 'und-u-ks-level1-kc-tr
</tip>
</sect3>
</sect2>
+
+ <sect2 id="collation-versions">
+ <title>Collation Versions</title>
+
+ <para>
+ The ordering defined by a collation is not necessarily fixed over time.
+ If a collation changes for any reason, persistent data structures such as
+ b-trees that depend on a stable ordering of text might be corrupted.
+ <productname>PostgreSQL</productname> defends against this by recording
+ the current version of each referenced collation for any index that
+ depends on it in the
+ <link linkend="catalog-pg-depend"><structname>pg_depend</structname></link>
+ catalog, if the collation provider makes it available. If the provider
+ later begins to report a different version, a warning will be issued
+ when the index is accessed, until either the <xref linkend="sql-reindex"/>
+ or the <xref linkend="sql-alterindex"/> command is used to update the
+ version.
+ </para>
+ <para>
+ Version information is available for collations from the
+ <literal>icu</literal> provider on all operating systems. For the
+ <literal>libc</literal> provider, versions are currently only available
+ on systems using the GNU C library (most Linux systems).
+ </para>
+
+ <note>
+ <para>
+ When using the GNU C library for collations, the C library's version
+ is used as a proxy for the collation version. Many Linux distributions
+ change collation definitions only when upgrading the C library, but this
+ approach is imperfect as maintainers are free to back-port newer
+ collation definitions to older C library releases.
+ </para>
+ </note>
+ </sect2>
</sect1>
<sect1 id="multibyte">
--
2.20.1
--o56keubw4jpehgac--
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Add memory/disk usage for WindowAgg nodes in EXPLAIN
@ 2024-09-14 08:12 Tatsuo Ishii <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Tatsuo Ishii @ 2024-09-14 08:12 UTC (permalink / raw)
To: [email protected]; +Cc: [email protected]; [email protected]; [email protected]; pgsql-hackers
>> > or the case when the last usage fit in memory but an earlier
>> > usage spilled to disk.
>>
>> In my understanding once tuplestore changes the storage type to disk,
>> it never returns to the memory storage type in terms of
>> tuplestore_get_stats. i.e. once state->usedDisk is set to true, it
>> never goes back to false. So the test case is not necessary.
>> David, am I correct?
>
> I understand that. I am requesting a testcase to test that same logic.
Maybe something like this? In the example below there are 2
partitions. the first one has 1998 rows and the second one has 2
rows. Assuming that work_mem is 64kB, the first one does not fit the
memory and spills to disk. The second partition fits memory. However as
state->usedDisk remains true, explain shows "Storage: Disk".
test=# explain (analyze,costs off) select sum(n) over(partition by m) from (SELECT n < 3 as m, n from generate_series(1,2000) a(n));
n QUERY PLAN
--------------------------------------------------------------------------------
-------------
WindowAgg (actual time=1.958..473328.589 rows=2000 loops=1)
Storage: Disk Maximum Storage: 65kB
-> Sort (actual time=1.008..1.277 rows=2000 loops=1)
Sort Key: ((a.n < 3))
Sort Method: external merge Disk: 48kB
-> Function Scan on generate_series a (actual time=0.300..0.633 rows=2
000 loops=1)
Planning Time: 0.069 ms
Execution Time: 474515.476 ms
(8 rows)
Best reagards,
--
Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp
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2020-03-11 02:01 [PATCH v27 5/5] Doc: Add Collation Versions section. Thomas Munro <[email protected]>
2024-09-14 08:12 Re: Add memory/disk usage for WindowAgg nodes in EXPLAIN Tatsuo Ishii <[email protected]>
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