From: Andrew Longwill <andrew@busuu.com>
To: "pgsql-general@lists.postgresql.org" <pgsql-general@lists.postgresql.org>
Subject: ERROR: could not attach to dynamic shared area
Thread-Topic: ERROR: could not attach to dynamic shared area
Thread-Index: AQHax9YD36ywoG3WsEq0Jsa2UtnTuw==
Date: Wed, 26 Jun 2024 14:43:30 +0000
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Hi all,

We=92re using Postgresql 15.4 in AWS RDS. Since yesterday we have seen two =
occurrences where our PHP application becomes unable to connect to our RDS =
replicas. In the application logs we see the error "FATAL: could not attach=
 to dynamic shared area". The RDS replica remains unusable in this state un=
less it=92s rebooted.

In the Postgresql replica logs we see the following errors just before the =
above error occurs: (I=92ve made the SELECT more succinct)

2024-06-25 21:04:36 UTC::@:[28757]:FATAL: terminating background worker "pa=
rallel worker" due to administrator command
2024-06-25 21:04:36 UTC::@:[28757]:STATEMENT: SELECT col1,..,col24 FROM my_=
table WHERE =85 DESC LIMIT 1
2024-06-25 21:04:36 UTC::@:[28758]:FATAL: terminating background worker "pa=
rallel worker" due to administrator command
2024-06-25 21:04:36 UTC::@:[28758]:STATEMENT: SELECT col1,..,col24 FROM my_=
table WHERE =85 DESC LIMIT 1
2024-06-25 21:04:36 UTC::@:[389]:LOG: background worker "parallel worker" (=
PID 28757) exited with exit code 1
2024-06-25 21:04:36 UTC::@:[389]:LOG: background worker "parallel worker" (=
PID 28758) exited with exit code 1

The same query is mentioned each time, however this is a query we=92ve been=
 running in production for many years. The query plan for that query is goo=
d.

AWS have advised that we try setting max_parallel_workers=3D0 and max_paral=
lel_workers_per_gather=3D0.

Can anyone advise on why we might be seeing this error suddenly?

Many thanks

Andrew

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<p class=3D"MsoNormal">Hi all,<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">We=92re using Postgresql 15.4 in AWS RDS. Since yest=
erday we have seen two occurrences where our PHP application becomes unable=
 to connect to our RDS replicas. In the application logs we see the error &=
quot;FATAL: could not attach to dynamic shared
 area&quot;. The RDS replica remains unusable in this state unless it=92s r=
ebooted.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">In the Postgresql replica logs we see the following =
errors just before the above error occurs: (I=92ve made the SELECT more suc=
cinct)<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">2024-06-25 21:04:36 UTC::@:[28757]:FATAL: terminatin=
g background worker &quot;parallel worker&quot; due to administrator comman=
d
<o:p></o:p></p>
<p class=3D"MsoNormal">2024-06-25 21:04:36 UTC::@:[28757]:STATEMENT: SELECT=
 col1,..,col24 FROM my_table WHERE =85 DESC LIMIT 1
<o:p></o:p></p>
<p class=3D"MsoNormal">2024-06-25 21:04:36 UTC::@:[28758]:FATAL: terminatin=
g background worker &quot;parallel worker&quot; due to administrator comman=
d
<o:p></o:p></p>
<p class=3D"MsoNormal">2024-06-25 21:04:36 UTC::@:[28758]:STATEMENT: SELECT=
 col1,..,col24 FROM my_table WHERE =85 DESC LIMIT 1<o:p></o:p></p>
<p class=3D"MsoNormal">2024-06-25 21:04:36 UTC::@:[389]:LOG: background wor=
ker &quot;parallel worker&quot; (PID 28757) exited with exit code 1
<o:p></o:p></p>
<p class=3D"MsoNormal">2024-06-25 21:04:36 UTC::@:[389]:LOG: background wor=
ker &quot;parallel worker&quot; (PID 28758) exited with exit code 1
<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">The same query is mentioned each time, however this =
is a query we=92ve been running in production for many years. The query pla=
n for that query is good.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">AWS have advised that we try setting max_parallel_wo=
rkers=3D0 and max_parallel_workers_per_gather=3D0.<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">Can anyone advise on why we might be seeing this err=
or suddenly?<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">Many thanks<o:p></o:p></p>
<p class=3D"MsoNormal"><o:p>&nbsp;</o:p></p>
<p class=3D"MsoNormal">Andrew<o:p></o:p></p>
</div>
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