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* [PATCH v49 5/7] Doc part of shared-memory based stats collector.
@ 2020-03-19 06:11 Kyotaro Horiguchi <[email protected]>
0 siblings, 0 replies; 5+ messages in thread
From: Kyotaro Horiguchi @ 2020-03-19 06:11 UTC (permalink / raw)
---
doc/src/sgml/catalogs.sgml | 6 +-
doc/src/sgml/config.sgml | 27 +++---
doc/src/sgml/high-availability.sgml | 13 +--
doc/src/sgml/monitoring.sgml | 127 +++++++++++++---------------
doc/src/sgml/ref/pg_dump.sgml | 9 +-
5 files changed, 86 insertions(+), 96 deletions(-)
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b1de6d0674..0ef684d4d0 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -9261,9 +9261,9 @@ SCRAM-SHA-256$<replaceable><iteration count></replaceable>:<replaceable>&l
<para>
<xref linkend="view-table"/> lists the system views described here.
More detailed documentation of each view follows below.
- There are some additional views that provide access to the results of
- the statistics collector; they are described in <xref
- linkend="monitoring-stats-views-table"/>.
+ There are some additional views that provide access to the activity
+ statistics; they are described in
+ <xref linkend="monitoring-stats-views-table"/>.
</para>
<para>
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 967de73596..753b1ab6f9 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -7375,11 +7375,11 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
<title>Run-time Statistics</title>
<sect2 id="runtime-config-statistics-collector">
- <title>Query and Index Statistics Collector</title>
+ <title>Query and Index Activity Statistics</title>
<para>
- These parameters control server-wide statistics collection features.
- When statistics collection is enabled, the data that is produced can be
+ These parameters control server-wide activity statistics features.
+ When activity statistics is enabled, the data that is produced can be
accessed via the <structname>pg_stat</structname> and
<structname>pg_statio</structname> family of system views.
Refer to <xref linkend="monitoring"/> for more information.
@@ -7395,14 +7395,13 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</term>
<listitem>
<para>
- Enables the collection of information on the currently
- executing command of each session, along with the time when
- that command began execution. This parameter is on by
- default. Note that even when enabled, this information is not
- visible to all users, only to superusers and the user owning
- the session being reported on, so it should not represent a
- security risk.
- Only superusers can change this setting.
+ Enables activity tracking on the currently executing command of
+ each session, along with the time when that command began
+ execution. This parameter is on by default. Note that even when
+ enabled, this information is not visible to all users, only to
+ superusers and the user owning the session being reported on, so it
+ should not represent a security risk. Only superusers can change this
+ setting.
</para>
</listitem>
</varlistentry>
@@ -7433,9 +7432,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</term>
<listitem>
<para>
- Enables collection of statistics on database activity.
+ Enables tracking of database activity.
This parameter is on by default, because the autovacuum
- daemon needs the collected information.
+ daemon needs the activity information.
Only superusers can change this setting.
</para>
</listitem>
@@ -8533,7 +8532,7 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
<listitem>
<para>
Specifies the fraction of the total number of heap tuples counted in
- the previous statistics collection that can be inserted without
+ the previously collected statistics that can be inserted without
incurring an index scan at the <command>VACUUM</command> cleanup stage.
This setting currently applies to B-tree indexes only.
</para>
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index f49f5c0108..45095857eb 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -2217,12 +2217,13 @@ HINT: You can then restart the server after making the necessary configuration
</para>
<para>
- The statistics collector is active during recovery. All scans, reads, blocks,
- index usage, etc., will be recorded normally on the standby. Replayed
- actions will not duplicate their effects on primary, so replaying an
- insert will not increment the Inserts column of pg_stat_user_tables.
- The stats file is deleted at the start of recovery, so stats from primary
- and standby will differ; this is considered a feature, not a bug.
+ The activity statistics is collected during recovery. All scans, reads,
+ blocks, index usage, etc., will be recorded normally on the
+ standby. Replayed actions will not duplicate their effects on primary, so
+ replaying an insert will not increment the Inserts column of
+ pg_stat_user_tables. The activity statistics is reset at the start of
+ recovery, so stats from primary and standby will differ; this is
+ considered a feature, not a bug.
</para>
<para>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 53692c0020..d4af6079aa 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -22,7 +22,7 @@
<para>
Several tools are available for monitoring database activity and
analyzing performance. Most of this chapter is devoted to describing
- <productname>PostgreSQL</productname>'s statistics collector,
+ <productname>PostgreSQL</productname>'s activity statistics,
but one should not neglect regular Unix monitoring programs such as
<command>ps</command>, <command>top</command>, <command>iostat</command>, and <command>vmstat</command>.
Also, once one has identified a
@@ -53,7 +53,6 @@ postgres 15554 0.0 0.0 57536 1184 ? Ss 18:02 0:00 postgres: back
postgres 15555 0.0 0.0 57536 916 ? Ss 18:02 0:00 postgres: checkpointer
postgres 15556 0.0 0.0 57536 916 ? Ss 18:02 0:00 postgres: walwriter
postgres 15557 0.0 0.0 58504 2244 ? Ss 18:02 0:00 postgres: autovacuum launcher
-postgres 15558 0.0 0.0 17512 1068 ? Ss 18:02 0:00 postgres: stats collector
postgres 15582 0.0 0.0 58772 3080 ? Ss 18:04 0:00 postgres: joe runbug 127.0.0.1 idle
postgres 15606 0.0 0.0 58772 3052 ? Ss 18:07 0:00 postgres: tgl regression [local] SELECT waiting
postgres 15610 0.0 0.0 58772 3056 ? Ss 18:07 0:00 postgres: tgl regression [local] idle in transaction
@@ -65,9 +64,8 @@ postgres 15610 0.0 0.0 58772 3056 ? Ss 18:07 0:00 postgres: tgl
primary server process. The command arguments
shown for it are the same ones used when it was launched. The next five
processes are background worker processes automatically launched by the
- primary process. (The <quote>stats collector</quote> process will not be present
- if you have set the system not to start the statistics collector; likewise
- the <quote>autovacuum launcher</quote> process can be disabled.)
+ primary process. (The <quote>autovacuum launcher</quote> process will not
+ be present if you have set the system not to start it.)
Each of the remaining
processes is a server process handling one client connection. Each such
process sets its command line display in the form
@@ -130,20 +128,21 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
</sect1>
<sect1 id="monitoring-stats">
- <title>The Statistics Collector</title>
+ <title>The Activity Statistics</title>
<indexterm zone="monitoring-stats">
<primary>statistics</primary>
</indexterm>
<para>
- <productname>PostgreSQL</productname>'s <firstterm>statistics collector</firstterm>
- is a subsystem that supports collection and reporting of information about
- server activity. Presently, the collector can count accesses to tables
- and indexes in both disk-block and individual-row terms. It also tracks
- the total number of rows in each table, and information about vacuum and
- analyze actions for each table. It can also count calls to user-defined
- functions and the total time spent in each one.
+ <productname>PostgreSQL</productname>'s <firstterm>activity
+ statistics</firstterm> is a subsystem that supports tracking and reporting
+ of information about server activity. Presently, the activity statistics
+ tracks the count of accesses to tables and indexes in both disk-block and
+ individual-row terms. It also tracks the total number of rows in each
+ table, and information about vacuum and analyze actions for each table. It
+ can also track calls to user-defined functions and the total time spent in
+ each one.
</para>
<para>
@@ -151,15 +150,15 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
information about exactly what is going on in the system right now, such as
the exact command currently being executed by other server processes, and
which other connections exist in the system. This facility is independent
- of the collector process.
+ of the activity statistics.
</para>
<sect2 id="monitoring-stats-setup">
- <title>Statistics Collection Configuration</title>
+ <title>Activity Statistics Configuration</title>
<para>
- Since collection of statistics adds some overhead to query execution,
- the system can be configured to collect or not collect information.
+ Since tracking for the activity statistics adds some overhead to query
+ execution, the system can be configured to track or not track activity.
This is controlled by configuration parameters that are normally set in
<filename>postgresql.conf</filename>. (See <xref linkend="runtime-config"/> for
details about setting configuration parameters.)
@@ -172,7 +171,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<para>
The parameter <xref linkend="guc-track-counts"/> controls whether
- statistics are collected about table and index accesses.
+ to track activity about table and index accesses.
</para>
<para>
@@ -196,18 +195,11 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
</para>
<para>
- The statistics collector transmits the collected information to other
- <productname>PostgreSQL</productname> processes through temporary files.
- These files are stored in the directory named by the
- <xref linkend="guc-stats-temp-directory"/> parameter,
- <filename>pg_stat_tmp</filename> by default.
- For better performance, <varname>stats_temp_directory</varname> can be
- pointed at a RAM-based file system, decreasing physical I/O requirements.
- When the server shuts down cleanly, a permanent copy of the statistics
- data is stored in the <filename>pg_stat</filename> subdirectory, so that
- statistics can be retained across server restarts. When recovery is
- performed at server start (e.g., after immediate shutdown, server crash,
- and point-in-time recovery), all statistics counters are reset.
+ down cleanly, a permanent copy of the statistics data is stored in
+ the <filename>pg_stat</filename> subdirectory, so that statistics can be
+ retained across server restarts. When recovery is performed at server
+ start (e.g. after immediate shutdown, server crash, and point-in-time
+ recovery), all statistics counters are reset.
</para>
</sect2>
@@ -220,48 +212,46 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
linkend="monitoring-stats-dynamic-views-table"/>, are available to show
the current state of the system. There are also several other
views, listed in <xref
- linkend="monitoring-stats-views-table"/>, available to show the results
- of statistics collection. Alternatively, one can
- build custom views using the underlying statistics functions, as discussed
- in <xref linkend="monitoring-stats-functions"/>.
+ linkend="monitoring-stats-views-table"/>, available to show the activity
+ statistics. Alternatively, one can build custom views using the underlying
+ statistics functions, as discussed in
+ <xref linkend="monitoring-stats-functions"/>.
</para>
<para>
- When using the statistics to monitor collected data, it is important
- to realize that the information does not update instantaneously.
- Each individual server process transmits new statistical counts to
- the collector just before going idle; so a query or transaction still in
- progress does not affect the displayed totals. Also, the collector itself
- emits a new report at most once per <varname>PGSTAT_STAT_INTERVAL</varname>
- milliseconds (500 ms unless altered while building the server). So the
- displayed information lags behind actual activity. However, current-query
- information collected by <varname>track_activities</varname> is
- always up-to-date.
+ When using the activity statistics, it is important to realize that the
+ information does not update instantaneously. Each individual server writes
+ out new statistical counts just before going idle, not frequent than once
+ per <varname>PGSTAT_STAT_INTERVAL</varname> milliseconds (1 second unless
+ altered while building the server); so a query or transaction still in
+ progress does not affect the displayed totals. However, current-query
+ information tracked by <varname>track_activities</varname> is always
+ up-to-date.
</para>
<para>
Another important point is that when a server process is asked to display
- any of these statistics, it first fetches the most recent report emitted by
- the collector process and then continues to use this snapshot for all
- statistical views and functions until the end of its current transaction.
- So the statistics will show static information as long as you continue the
- current transaction. Similarly, information about the current queries of
- all sessions is collected when any such information is first requested
- within a transaction, and the same information will be displayed throughout
- the transaction.
- This is a feature, not a bug, because it allows you to perform several
- queries on the statistics and correlate the results without worrying that
- the numbers are changing underneath you. But if you want to see new
- results with each query, be sure to do the queries outside any transaction
- block. Alternatively, you can invoke
+ any of these statistics, it first reads the current statistics and then
+ continues to use this snapshot for all statistical views and functions
+ until the end of its current transaction. So the statistics will show
+ static information as long as you continue the current transaction.
+ Similarly, information about the current queries of all sessions is tracked
+ when any such information is first requested within a transaction, and the
+ same information will be displayed throughout the transaction. This is a
+ feature, not a bug, because it allows you to perform several queries on the
+ statistics and correlate the results without worrying that the numbers are
+ changing underneath you. But if you want to see new results with each
+ query, be sure to do the queries outside any transaction block.
+ Alternatively, you can invoke
<function>pg_stat_clear_snapshot</function>(), which will discard the
current transaction's statistics snapshot (if any). The next use of
statistical information will cause a new snapshot to be fetched.
</para>
-
+
<para>
- A transaction can also see its own statistics (as yet untransmitted to the
- collector) in the views <structname>pg_stat_xact_all_tables</structname>,
+ A transaction can also see its own statistics (as yet unwritten to the
+ server-wide activity statistics) in the
+ views <structname>pg_stat_xact_all_tables</structname>,
<structname>pg_stat_xact_sys_tables</structname>,
<structname>pg_stat_xact_user_tables</structname>, and
<structname>pg_stat_xact_user_functions</structname>. These numbers do not act as
@@ -643,7 +633,7 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
kernel's I/O cache, and might therefore still be fetched without
requiring a physical read. Users interested in obtaining more
detailed information on <productname>PostgreSQL</productname> I/O behavior are
- advised to use the <productname>PostgreSQL</productname> statistics collector
+ advised to use the <productname>PostgreSQL</productname> activity statistics
in combination with operating system utilities that allow insight
into the kernel's handling of I/O.
</para>
@@ -1080,10 +1070,6 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>LogicalLauncherMain</literal></entry>
<entry>Waiting in main loop of logical replication launcher process.</entry>
</row>
- <row>
- <entry><literal>PgStatMain</literal></entry>
- <entry>Waiting in main loop of statistics collector process.</entry>
- </row>
<row>
<entry><literal>RecoveryWalStream</literal></entry>
<entry>Waiting in main loop of startup process for WAL to arrive, during
@@ -1838,6 +1824,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
</thead>
<tbody>
+ <row>
+ <entry><literal>ActivityStatistics</literal></entry>
+ <entry>Waiting to write out activity statistics to shared memory.</entry>
+ </row>
<row>
<entry><literal>AddinShmemInit</literal></entry>
<entry>Waiting to manage an extension's space allocation in shared
@@ -6061,9 +6051,10 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
<entry><literal>performing final cleanup</literal></entry>
<entry>
<command>VACUUM</command> is performing final cleanup. During this phase,
- <command>VACUUM</command> will vacuum the free space map, update statistics
- in <literal>pg_class</literal>, and report statistics to the statistics
- collector. When this phase is completed, <command>VACUUM</command> will end.
+ <command>VACUUM</command> will vacuum the free space map, update
+ statistics in <literal>pg_class</literal>, and system-wide activity
+ statistics. When this phase is completed, <command>VACUUM</command>
+ will end.
</entry>
</row>
</tbody>
diff --git a/doc/src/sgml/ref/pg_dump.sgml b/doc/src/sgml/ref/pg_dump.sgml
index bcbb7a25fb..1fa59a2fdf 100644
--- a/doc/src/sgml/ref/pg_dump.sgml
+++ b/doc/src/sgml/ref/pg_dump.sgml
@@ -1280,11 +1280,10 @@ PostgreSQL documentation
</para>
<para>
- The database activity of <application>pg_dump</application> is
- normally collected by the statistics collector. If this is
- undesirable, you can set parameter <varname>track_counts</varname>
- to false via <envar>PGOPTIONS</envar> or the <literal>ALTER
- USER</literal> command.
+ The database activity of <application>pg_dump</application> is normally
+ collected. If this is undesirable, you can set
+ parameter <varname>track_counts</varname> to false
+ via <envar>PGOPTIONS</envar> or the <literal>ALTER USER</literal> command.
</para>
</refsect1>
--
2.27.0
----Next_Part(Tue_Mar__9_16_53_11_2021_575)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
filename="v49-0006-Remove-the-GUC-stats_temp_directory.patch"
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Query execution in Perl TAP tests needs work
@ 2023-08-28 13:23 Andrew Dunstan <[email protected]>
0 siblings, 2 replies; 5+ messages in thread
From: Andrew Dunstan @ 2023-08-28 13:23 UTC (permalink / raw)
To: Thomas Munro <[email protected]>; pgsql-hackers
On 2023-08-28 Mo 01:29, Thomas Munro wrote:
> Hi,
>
> Every time we run a SQL query, we fork a new psql process and a new
> cold backend process. It's not free on Unix, and quite a lot worse on
> Windows, at around 70ms per query. Take amcheck/001_verify_heapam for
> example. It runs 272 subtests firing off a stream of queries, and
> completes in ~51s on Windows (!), and ~6-9s on the various Unixen, on
> CI.
>
> Here are some timestamps I captured from CI by instrumenting various
> Perl and C bits:
>
> 0.000s: IPC::Run starts
> 0.023s: postmaster socket sees connection
> 0.025s: postmaster has created child process
> 0.033s: backend starts running main()
> 0.039s: backend has reattached to shared memory
> 0.043s: backend connection authorized message
> 0.046s: backend has executed and logged query
> 0.070s: IPC::Run returns
>
> I expected process creation to be slow on that OS, but it seems like
> something happening at the end is even slower. CI shows Windows
> consuming 4 CPUs at 100% for a full 10 minutes to run a test suite
> that finishes in 2-3 minutes everywhere else with the same number of
> CPUs. Could there be an event handling snafu in IPC::Run or elsewhere
> nearby? It seems like there must be either a busy loop or a busted
> sleep/wakeup... somewhere? But even if there's a weird bug here
> waiting to be discovered and fixed, I guess it'll always be too slow
> at ~10ms per process spawned, with two processes to spawn, and it's
> bad enough on Unix.
>
> As an experiment, I hacked up a not-good-enough-to-share experiment
> where $node->safe_psql() would automatically cache a BackgroundPsql
> object and reuse it, and the times for that test dropped ~51 -> ~9s on
> Windows, and ~7 -> ~2s on the Unixen. But even that seems non-ideal
> (well it's certainly non-ideal the way I hacked it up anyway...). I
> suppose there are quite a few ways we could do better:
>
> 1. Don't fork anything at all: open (and cache) a connection directly
> from Perl.
> 1a. Write xsub or ffi bindings for libpq. Or vendor (parts) of the
> popular Perl xsub library?
> 1b. Write our own mini pure-perl pq client module. Or vendor (parts)
> of some existing one.
> 2. Use long-lived psql sessions.
> 2a. Something building on BackgroundPsql.
> 2b. Maybe give psql or a new libpq-wrapper a new low level stdio/pipe
> protocol that is more fun to talk to from Perl/machines?
>
> In some other languages one can do FFI pretty easily so we could use
> the in-tree libpq without extra dependencies:
>
>>>> import ctypes
>>>> libpq = ctypes.cdll.LoadLibrary("/path/to/libpq.so")
>>>> libpq.PQlibVersion()
> 170000
>
> ... but it seems you can't do either static C bindings or runtime FFI
> from Perl without adding a new library/package dependency. I'm not
> much of a Perl hacker so I don't have any particular feeling. What
> would be best?
>
> This message brought to you by the Lorax.
Thanks for raising this. Windows test times have bothered me for ages.
The standard perl DBI library has a connect_cached method. Of course we
don't want to be dependent on it, especially if we might have changed
libpq in what we're testing, and it would place a substantial new burden
on testers like buildfarm owners.
I like the idea of using a pure perl pq implementation, not least
because it could expand our ability to test things at the protocol
level. Not sure how much work it would be. I'm willing to help if we
want to go that way.
Yes you need an external library to use FFI in perl, but there's one
that's pretty tiny. See <https://metacpan.org/pod/FFI::Library;. There
is also FFI::Platypus, but it involves building a library. OTOH, that's
the one that's available standard on my Fedora and Ubuntu systems. I
haven't tried using either Maybe we could use some logic that would use
the FFI interface if it's available, and fall back on current usage.
cheers
andrew
--
Andrew Dunstan
EDB:https://www.enterprisedb.com
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Query execution in Perl TAP tests needs work
@ 2023-08-29 04:33 Thomas Munro <[email protected]>
parent: Andrew Dunstan <[email protected]>
1 sibling, 0 replies; 5+ messages in thread
From: Thomas Munro @ 2023-08-29 04:33 UTC (permalink / raw)
To: Andrew Dunstan <[email protected]>; +Cc: pgsql-hackers
On Tue, Aug 29, 2023 at 1:23 AM Andrew Dunstan <[email protected]> wrote:
> I like the idea of using a pure perl pq implementation, not least because it could expand our ability to test things at the protocol level. Not sure how much work it would be. I'm willing to help if we want to go that way.
Cool. Let's see what others think.
And assuming we can pick *something* vaguely efficient and find a Perl
hacker to implement it, a related question is how to expose it to our
test suites.
Should we figure out how to leave all our tests unchanged, by teaching
$node->psql() et al to do caching implicitly? Or should we make it
explicit, with $conn = $node->connect(), and $conn->do_stuff()? And
if the latter, should do_stuff be DBI style or something that suits us
better?
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Query execution in Perl TAP tests needs work
@ 2023-08-30 22:32 Andrew Dunstan <[email protected]>
parent: Andrew Dunstan <[email protected]>
1 sibling, 1 reply; 5+ messages in thread
From: Andrew Dunstan @ 2023-08-30 22:32 UTC (permalink / raw)
To: Thomas Munro <[email protected]>; pgsql-hackers
On 2023-08-28 Mo 09:23, Andrew Dunstan wrote:
>
>
> On 2023-08-28 Mo 01:29, Thomas Munro wrote:
>> Hi,
>>
>> Every time we run a SQL query, we fork a new psql process and a new
>> cold backend process. It's not free on Unix, and quite a lot worse on
>> Windows, at around 70ms per query. Take amcheck/001_verify_heapam for
>> example. It runs 272 subtests firing off a stream of queries, and
>> completes in ~51s on Windows (!), and ~6-9s on the various Unixen, on
>> CI.
>>
>> Here are some timestamps I captured from CI by instrumenting various
>> Perl and C bits:
>>
>> 0.000s: IPC::Run starts
>> 0.023s: postmaster socket sees connection
>> 0.025s: postmaster has created child process
>> 0.033s: backend starts running main()
>> 0.039s: backend has reattached to shared memory
>> 0.043s: backend connection authorized message
>> 0.046s: backend has executed and logged query
>> 0.070s: IPC::Run returns
>>
>> I expected process creation to be slow on that OS, but it seems like
>> something happening at the end is even slower. CI shows Windows
>> consuming 4 CPUs at 100% for a full 10 minutes to run a test suite
>> that finishes in 2-3 minutes everywhere else with the same number of
>> CPUs. Could there be an event handling snafu in IPC::Run or elsewhere
>> nearby? It seems like there must be either a busy loop or a busted
>> sleep/wakeup... somewhere? But even if there's a weird bug here
>> waiting to be discovered and fixed, I guess it'll always be too slow
>> at ~10ms per process spawned, with two processes to spawn, and it's
>> bad enough on Unix.
>>
>> As an experiment, I hacked up a not-good-enough-to-share experiment
>> where $node->safe_psql() would automatically cache a BackgroundPsql
>> object and reuse it, and the times for that test dropped ~51 -> ~9s on
>> Windows, and ~7 -> ~2s on the Unixen. But even that seems non-ideal
>> (well it's certainly non-ideal the way I hacked it up anyway...). I
>> suppose there are quite a few ways we could do better:
>>
>> 1. Don't fork anything at all: open (and cache) a connection directly
>> from Perl.
>> 1a. Write xsub or ffi bindings for libpq. Or vendor (parts) of the
>> popular Perl xsub library?
>> 1b. Write our own mini pure-perl pq client module. Or vendor (parts)
>> of some existing one.
>> 2. Use long-lived psql sessions.
>> 2a. Something building on BackgroundPsql.
>> 2b. Maybe give psql or a new libpq-wrapper a new low level stdio/pipe
>> protocol that is more fun to talk to from Perl/machines?
>>
>> In some other languages one can do FFI pretty easily so we could use
>> the in-tree libpq without extra dependencies:
>>
>>>>> import ctypes
>>>>> libpq = ctypes.cdll.LoadLibrary("/path/to/libpq.so")
>>>>> libpq.PQlibVersion()
>> 170000
>>
>> ... but it seems you can't do either static C bindings or runtime FFI
>> from Perl without adding a new library/package dependency. I'm not
>> much of a Perl hacker so I don't have any particular feeling. What
>> would be best?
>>
>> This message brought to you by the Lorax.
>
> Thanks for raising this. Windows test times have bothered me for ages.
>
> The standard perl DBI library has a connect_cached method. Of course
> we don't want to be dependent on it, especially if we might have
> changed libpq in what we're testing, and it would place a substantial
> new burden on testers like buildfarm owners.
>
> I like the idea of using a pure perl pq implementation, not least
> because it could expand our ability to test things at the protocol
> level. Not sure how much work it would be. I'm willing to help if we
> want to go that way.
>
> Yes you need an external library to use FFI in perl, but there's one
> that's pretty tiny. See <https://metacpan.org/pod/FFI::Library;. There
> is also FFI::Platypus, but it involves building a library. OTOH,
> that's the one that's available standard on my Fedora and Ubuntu
> systems. I haven't tried using either Maybe we could use some logic
> that would use the FFI interface if it's available, and fall back on
> current usage.
>
>
>
I had a brief play with this. Here's how easy it was to wrap libpq in perl:
#!/usr/bin/perl
use strict; use warnings;
use FFI::Platypus;
my $ffi = FFI::Platypus->new(api=>1);
$ffi->lib("inst/lib/libpq.so");
$ffi->type('opaque' => 'PGconn');
$ffi->attach(PQconnectdb => [ 'string' ] => 'PGconn');
$ffi->attach(PQfinish => [ 'PGconn' ] => 'void');
$ffi->type('opaque' => 'PGresult');
$ffi->attach(PQexec => [ 'PGconn', 'string' ] => 'PGresult');
$ffi->attach(PQgetvalue => [ 'PGresult', 'int', 'int' ] => 'string');
my $pgconn = PQconnectdb("dbname=postgres host=/tmp");
my $res = PQexec($pgconn, "select count(*) from pg_class");
my $count = PQgetvalue( $res, 0, 0);
print "count: $count\n";
PQfinish($pgconn);
cheers
andrew
--
Andrew Dunstan
EDB:https://www.enterprisedb.com
^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: Query execution in Perl TAP tests needs work
@ 2023-08-31 01:29 Thomas Munro <[email protected]>
parent: Andrew Dunstan <[email protected]>
0 siblings, 0 replies; 5+ messages in thread
From: Thomas Munro @ 2023-08-31 01:29 UTC (permalink / raw)
To: Andrew Dunstan <[email protected]>; +Cc: pgsql-hackers
On Thu, Aug 31, 2023 at 10:32 AM Andrew Dunstan <[email protected]> wrote:
> #!/usr/bin/perl
>
> use strict; use warnings;
>
> use FFI::Platypus;
>
> my $ffi = FFI::Platypus->new(api=>1);
> $ffi->lib("inst/lib/libpq.so");
>
>
> $ffi->type('opaque' => 'PGconn');
> $ffi->attach(PQconnectdb => [ 'string' ] => 'PGconn');
> $ffi->attach(PQfinish => [ 'PGconn' ] => 'void');
>
> $ffi->type('opaque' => 'PGresult');
> $ffi->attach(PQexec => [ 'PGconn', 'string' ] => 'PGresult');
> $ffi->attach(PQgetvalue => [ 'PGresult', 'int', 'int' ] => 'string');
>
> my $pgconn = PQconnectdb("dbname=postgres host=/tmp");
> my $res = PQexec($pgconn, "select count(*) from pg_class");
> my $count = PQgetvalue( $res, 0, 0);
>
> print "count: $count\n";
>
> PQfinish($pgconn);
It looks very promising so far. How hard would it be for us to add
this dependency? Mostly pinging build farm owners?
I'm still on the fence, but the more I know about IPC::Run, the better
the various let's-connect-directly-from-Perl options sound...
^ permalink raw reply [nested|flat] 5+ messages in thread
end of thread, other threads:[~2023-08-31 01:29 UTC | newest]
Thread overview: 5+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2020-03-19 06:11 [PATCH v49 5/7] Doc part of shared-memory based stats collector. Kyotaro Horiguchi <[email protected]>
2023-08-28 13:23 Re: Query execution in Perl TAP tests needs work Andrew Dunstan <[email protected]>
2023-08-29 04:33 ` Re: Query execution in Perl TAP tests needs work Thomas Munro <[email protected]>
2023-08-30 22:32 ` Re: Query execution in Perl TAP tests needs work Andrew Dunstan <[email protected]>
2023-08-31 01:29 ` Re: Query execution in Perl TAP tests needs work Thomas Munro <[email protected]>
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