Hi,
On Thu, Dec 05, 2024 at 05:51:11PM +0900, Masahiro Ikeda wrote:
> Hi,
>
> I recently encountered a case where having this feature would have been very
> helpful.
Oh great, thanks for the feedback!
> Thank you for developing it! I have a few questions and comments.
>
> Here are questions:
>
> After this patch is merged, are you considering adding delayed_time
> information to the logs output by log_autovacuum_min_duration?
> In the case I experienced, it would have been great to easily understand
> how much of the total execution time was spent on timed delays from the
> already executed VACUUM logs.
That's a good point. We already discussed adding some information in a dedicated
view ([1]) (and that's an idea I keep in mind). I also think your idea is worth
it and that it would make sense to start a dedicated thread once this one is
merged.
> Recently, this thread has not been active.
I think than Nathan wants to give time to others to interact on it like you
do ;-) (Nathan please correct me if I'm wrong).
> Here are minor comments on the v7 patch:
Thanks!
> Why not use the <xref> element, for example, <xref
> linkend="guc-autovacuum-vacuum-cost-delay"/>,
> as in the max_dead_tuple_bytes column?
There is multiple places where "<varname>vacuum_cost_delay</varname>" is
being used but I agree that's better to be consistent with how it is done for
this view. Done in v8 attached.
> IIUC, only the worker updates the column at a 1 Hz frequency. Would it be
> better to rephrase the following?"
> * The workers update the column no more frequently than once per second,
> so it could show slightly old values.
Yeah I like the re-wording, done that way in v8.
> + if (INSTR_TIME_GET_MILLISEC(time_since_last_report) >
> WORKER_REPORT_DELAY_INTERVAL)
> + {
> +
> pgstat_progress_parallel_incr_param(PROGRESS_VACUUM_TIME_DELAYED,
> +
> nap_time_since_last_report);
> + nap_time_since_last_report = 0;
> + last_report_time = delay_end;
> + }
>
> IIUC, unsent delayed_time will disappear when the parallel workers exit
> because they are not considered in parallel_vacuum_end(). I assume this
> is intentional behavior, as it is an acceptable error for the use cases.
Yeah, people would likely use this new field to monitor long running vacuum.
Long enough that this error should be acceptable. Do you agree?
> I didn't see any comments regarding this, so I wanted to confirm.
Added a comment to make it clear, thanks!
[1]:
https://www.postgresql.org/message-id/CAD21AoDOu%3DDZcC%2BPemYmCNGSwbgL1s-5OZkZ1Spd5pSxofWNCw%40mail.gmail.com
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
>From fc4b761a917804e6e7de46868d388a41735d8cca Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot...@gmail.com>
Date: Mon, 24 Jun 2024 08:43:26 +0000
Subject: [PATCH v8] Report the total amount of time that vacuum has been
delayed due to cost delay
This commit adds one column: time_delayed to the pg_stat_progress_vacuum system
view to show the total amount of time in milliseconds that vacuum has been
delayed.
This uses the new parallel message type for progress reporting added
by f1889729dd.
In case of parallel worker, to avoid the leader to be interrupted too frequently
(while it might be sleeping for cost delay), the report is done only if the last
report has been done more than 1 second ago.
Having a time based only approach to throttle the reporting of the parallel
workers sounds reasonable.
Indeed when deciding about the throttling:
1. The number of parallel workers should not come into play:
1.1) the more parallel workers is used, the less the impact of the leader on
the vacuum index phase duration/workload is (because the repartition is done
on more processes).
1.2) the less parallel workers is, the less the leader will be interrupted (
less parallel workers would report their delayed time).
2. The cost limit should not come into play as that value is distributed
proportionally among the parallel workers (so we're back to the previous point).
3. The cost delay does not come into play as the leader could be interrupted at
the beginning, the midle or whatever part of the wait and we are more interested
about the frequency of the interrupts.
3. A 1 second reporting "throttling" looks a reasonable threshold as:
3.1 the idea is to have a significant impact when the leader could have been
interrupted say hundred/thousand times per second.
3.2 it does not make that much sense for any tools to sample pg_stat_progress_vacuum
multiple times per second (so a one second reporting granularity seems ok).
Would need to bump catversion because this changes the definition of
pg_stat_progress_vacuum.
---
doc/src/sgml/monitoring.sgml | 13 +++++++
src/backend/catalog/system_views.sql | 2 +-
src/backend/commands/vacuum.c | 53 ++++++++++++++++++++++++++++
src/include/commands/progress.h | 1 +
src/test/regress/expected/rules.out | 3 +-
5 files changed, 70 insertions(+), 2 deletions(-)
22.8% doc/src/sgml/
4.0% src/backend/catalog/
67.6% src/backend/commands/
3.8% src/test/regress/expected/
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 840d7f8161..7386f7333d 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -6428,6 +6428,19 @@ FROM pg_stat_get_backend_idset() AS backendid;
<literal>cleaning up indexes</literal>.
</para></entry>
</row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>time_delayed</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Total amount of time spent in milliseconds waiting due to <xref linkend="guc-vacuum-cost-delay"/>
+ or <xref linkend="guc-autovacuum-vacuum-cost-delay"/>. In case of parallel
+ vacuum the reported time is across all the workers and the leader. The
+ workers update the column no more frequently than once per second, so it
+ could show slightly old values.
+ </para></entry>
+ </row>
</tbody>
</tgroup>
</table>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index da9a8fe99f..013bd06222 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1222,7 +1222,7 @@ CREATE VIEW pg_stat_progress_vacuum AS
S.param4 AS heap_blks_vacuumed, S.param5 AS index_vacuum_count,
S.param6 AS max_dead_tuple_bytes, S.param7 AS dead_tuple_bytes,
S.param8 AS num_dead_item_ids, S.param9 AS indexes_total,
- S.param10 AS indexes_processed
+ S.param10 AS indexes_processed, S.param11 AS time_delayed
FROM pg_stat_get_progress_info('VACUUM') AS S
LEFT JOIN pg_database D ON S.datid = D.oid;
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index bb639ef51f..6f9e515f56 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -39,6 +39,7 @@
#include "catalog/pg_inherits.h"
#include "commands/cluster.h"
#include "commands/defrem.h"
+#include "commands/progress.h"
#include "commands/vacuum.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
@@ -59,6 +60,16 @@
#include "utils/snapmgr.h"
#include "utils/syscache.h"
+/*
+ * Minimum amount of time (in ms) between two reports of the delayed time from a
+ * parallel worker to the leader. The goal is to avoid the leader to be
+ * interrupted too frequently while it might be sleeping for cost delay.
+ *
+ * Note that unsent delayed_time will disappear when the parallel workers exit
+ * because they are not considered in parallel_vacuum_end(). That's an acceptable
+ * error for the use cases.
+ */
+#define WORKER_REPORT_DELAY_INTERVAL 1000
/*
* GUC parameters
@@ -102,6 +113,16 @@ pg_atomic_uint32 *VacuumSharedCostBalance = NULL;
pg_atomic_uint32 *VacuumActiveNWorkers = NULL;
int VacuumCostBalanceLocal = 0;
+/*
+ * In case of parallel workers, the last time the delay has been reported to
+ * the leader.
+ * We assume this initializes to zero.
+ */
+static instr_time last_report_time;
+
+/* total nap time between two reports */
+static double nap_time_since_last_report = 0;
+
/* non-export function prototypes */
static List *expand_vacuum_rel(VacuumRelation *vrel,
MemoryContext vac_context, int options);
@@ -2402,13 +2423,45 @@ vacuum_delay_point(void)
/* Nap if appropriate */
if (msec > 0)
{
+ instr_time delay_start;
+ instr_time delay_end;
+ instr_time delayed_time;
+
if (msec > vacuum_cost_delay * 4)
msec = vacuum_cost_delay * 4;
pgstat_report_wait_start(WAIT_EVENT_VACUUM_DELAY);
+ INSTR_TIME_SET_CURRENT(delay_start);
pg_usleep(msec * 1000);
+ INSTR_TIME_SET_CURRENT(delay_end);
pgstat_report_wait_end();
+ /* Report the amount of time we slept */
+ INSTR_TIME_SET_ZERO(delayed_time);
+ INSTR_TIME_ACCUM_DIFF(delayed_time, delay_end, delay_start);
+
+ /* Parallel worker */
+ if (IsParallelWorker())
+ {
+ instr_time time_since_last_report;
+
+ INSTR_TIME_SET_ZERO(time_since_last_report);
+ INSTR_TIME_ACCUM_DIFF(time_since_last_report, delay_end,
+ last_report_time);
+ nap_time_since_last_report += INSTR_TIME_GET_MILLISEC(delayed_time);
+
+ if (INSTR_TIME_GET_MILLISEC(time_since_last_report) > WORKER_REPORT_DELAY_INTERVAL)
+ {
+ pgstat_progress_parallel_incr_param(PROGRESS_VACUUM_TIME_DELAYED,
+ nap_time_since_last_report);
+ nap_time_since_last_report = 0;
+ last_report_time = delay_end;
+ }
+ }
+ else
+ pgstat_progress_incr_param(PROGRESS_VACUUM_TIME_DELAYED,
+ INSTR_TIME_GET_MILLISEC(delayed_time));
+
/*
* We don't want to ignore postmaster death during very long vacuums
* with vacuum_cost_delay configured. We can't use the usual
diff --git a/src/include/commands/progress.h b/src/include/commands/progress.h
index 5616d64523..9a0c2358c6 100644
--- a/src/include/commands/progress.h
+++ b/src/include/commands/progress.h
@@ -28,6 +28,7 @@
#define PROGRESS_VACUUM_NUM_DEAD_ITEM_IDS 7
#define PROGRESS_VACUUM_INDEXES_TOTAL 8
#define PROGRESS_VACUUM_INDEXES_PROCESSED 9
+#define PROGRESS_VACUUM_TIME_DELAYED 10
/* Phases of vacuum (as advertised via PROGRESS_VACUUM_PHASE) */
#define PROGRESS_VACUUM_PHASE_SCAN_HEAP 1
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 3014d047fe..8b1154efac 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2056,7 +2056,8 @@ pg_stat_progress_vacuum| SELECT s.pid,
s.param7 AS dead_tuple_bytes,
s.param8 AS num_dead_item_ids,
s.param9 AS indexes_total,
- s.param10 AS indexes_processed
+ s.param10 AS indexes_processed,
+ s.param11 AS time_delayed
FROM (pg_stat_get_progress_info('VACUUM'::text) s(pid, datid, relid, param1, param2, param3, param4, param5, param6, param7, param8, param9, param10, param11, param12, param13, param14, param15, param16, param17, param18, param19, param20)
LEFT JOIN pg_database d ON ((s.datid = d.oid)));
pg_stat_recovery_prefetch| SELECT stats_reset,
--
2.34.1
