[pgpool-general: 9493] Re: Weird error in pgpool 4.6 logs: WARNING: failed to lock semaphore
Tatsuo Ishii
ishii at postgresql.org
Mon Jun 2 18:47:43 JST 2025
> Hi,
> I tried the strace as you shown but it didn't really output anything:
>
> $ sudo strace -p 1662563 -f -tt --trace=ipc
> strace: Process 1662563 attached
>
> ^Cstrace: Process 1662563 detached. <--- this is me getting out of it,
> since I saw in another window the semaphores were gone already, without
> anything outputting here. Unless something's wrong with the syntax of the
> command, it didn't really output anything. I changed the log line you
> suggested as well.
>
> Also, FYI - I tried to downgrade to a lower (4.3.7) version as it was
> available in my package repository, and the same semaphore version persists,
Okay. I think you need to start pgpool from strace. I mean, modifiy
pgpool.service from:
ExecStart=/usr/sbin/pgpool -f /etc/pgpool2/pgpool.conf $OPTS
to:
ExecStart=strace -f -tt --trace=ipc /usr/sbin/pgpool -f /etc/pgpool2/pgpool.conf $OPTS
> On Mon, Jun 2, 2025 at 2:40 AM Tatsuo Ishii <ishii at postgresql.org> wrote:
>
>> > Hi,
>> > Not sure I can patch the source, as it was installed via apt get and not
>> > compiled from source. If that is doable to a package-built one and you
>> can
>> > give me some instructions, I can certainly try.
>>
>> Unfortunately I'm not familiar with debian packaging.
>>
>> > As for the pgpool log, I'm attaching it, hopefully it will go through,
>> it's
>> > about 5mb as I enabled higher debug options.
>>
>> It was sent as a direct mail to me. Not sure who/what removed the
>> semaphore. I observe following from the log anyway:
>>
>> - pgpool started on 16:10:21. At that time the semaphore definitely
>> existed.
>> - Until 16:15:13, everything worked great.
>> - On 16:15:23, the problem started.
>>
>> So it seems the semaphore was removed by someone between 16:15:13 and
>> 16:15:23.
>>
>> Unfortunately the removal of semaphore was not recorded in the log. To
>> determine who removed the semaphore, can you please attach strace to
>> pgpool main and share the log? This time debug log is not necessary.
>>
>> - Find the pgpool parent process pid (in the debug log it was 1483510)
>> - Become root (attaching strace usually requires root privilege)
>> - Attach strace to the process $pid
>>
>> strace -p $pid -f -tt --trace=ipc
>>
>> -f: (follow the child process of pgpool main)
>> -tt: add timestamp with milliseconds
>> --trace=ipc: limit the tracing system call to ipc to reduce the log
>>
>> BTW, I recommend yo to set log_line_prefix to something like this so
>> that you can take milliseconds log (%m) and process application name
>> (%a). They are usable in 4.6.
>>
>> log_line_prefix = '%m: %a pid %p: '
>>
>> > On Sun, Jun 1, 2025 at 4:20 PM Tatsuo Ishii <ishii at postgresql.org>
>> wrote:
>> >
>> >> > To your points/questions:
>> >> > 1) version is 4.6.1 - the source I'm using (via apt get) doesn't have
>> >> 4.6.2
>> >> > yet
>> >>
>> >> Ok.
>> >>
>> >> > 2) ipcs -s shows... nothing, literally. Checked all nodes, i.e.
>> >> >
>> >> > postgres at db-replica3:~$ ipcs -s
>> >> >
>> >> > ------ Semaphore Arrays --------
>> >> > key semid owner perms nsems
>> >> >
>> >> > Also, it kinda seems like "failed to unlock semaphore" shows during
>> >> startup
>> >> > of pgpool and while it's running, but maybe I'm not reading the log
>> >> > properly.
>> >>
>> >> So pgpool lost semaphore soon after starting. Can you share full
>> >> pgpool log before "failed to unlock semaphore" appears?
>> >>
>> >> > 3) regarding heartbeats, my pgpool.conf has it roughly like this:
>> >> >
>> >> > heartbeat_hostname0 = 'db-primary-priv'
>> >> > heartbeat_port0 = 9694
>> >> > heartbeat_device0 = ''
>> >> >
>> >> > heartbeat_hostname1 = 'db-replica1-priv'
>> >> > heartbeat_port1 = 9694
>> >> > heartbeat_device1 = ''
>> >> >
>> >> > heartbeat_hostname2 = 'db-replica2-priv'
>> >> > heartbeat_port2 = 9694
>> >> > heartbeat_device2 = ''
>> >> >
>> >> > heartbeat_hostname3 = 'db-replica3-priv'
>> >> > heartbeat_port3 = 9694
>> >> > heartbeat_device3 = ''
>> >>
>> >> Looks normal.
>> >>
>> >> I have checked the pgpool source code and found suspicious
>> >> code. before 4.6, pgpool heartbeart receiver process binds to any
>> >> address on the host. However from 4.6 pgpool binds to only loop back
>> >> address, which is plain wrong. Is it possible for you to patch the
>> >> pgpool source code and build pgpool binary?
>> >>
>> >> > So it seems likely that the inability to lock/unlock semaphores is the
>> >> > problem, question is why and how do I resolve it? :(
>> >>
>> >> Currently I have no idea. That's why I am requesting the pgpool log.
>> >>
>> >> > I'll c/p parts of my pgpool.service file as well, in case you may see
>> >> > something 'off' in it?
>> >> >
>> >> >
>> >> > [Service]
>> >> > User=postgres
>> >> > Group=postgres
>> >> >
>> >> > EnvironmentFile=-/etc/default/pgpool2
>> >> >
>> >> > ExecStart=/usr/sbin/pgpool -f /etc/pgpool2/pgpool.conf $OPTS
>> >> > ExecStop=/usr/sbin/pgpool -f /etc/pgpool2/pgpool.conf $STOP_OPTS stop
>> >> > ExecReload=/usr/sbin/pgpool -f /etc/pgpool2/pgpool.conf reload
>> >> > LimitNOFILE=65536:65536
>> >> > LimitNPROC=16384:16384
>> >> > LimitSTACK=10485760:33554432
>> >> > LimitMEMLOCK=infinity
>> >> > LimitDATA=infinity
>> >> >
>> >> >
>> >> > Thanks in advance.
>> >> >
>> >> > On Sun, Jun 1, 2025 at 2:06 PM Tatsuo Ishii <ishii at postgresql.org>
>> >> wrote:
>> >> >
>> >> >> > Hi,
>> >> >> > So long story short, I'm migrating a PG13 cluster from RHEL to
>> Ubuntu
>> >> >> > 24.04. In the process, the pgpool version is also being upgraded to
>> >> 4.6
>> >> >> > (from 4.2).
>> >> >>
>> >> >> What is the exact version of 4.6? I am asking because 4.6.0 has
>> >> >> vulnerability.
>> >> >>
>> >> >>
>> >>
>> https://pgpool.net/mediawiki/index.php/Main_Page#Pgpool-II_4.6.1.2C_4.5.7.2C_4.4.12.2C_4.3.15_and_4.2.22_officially_released_.282025.2F05.2F15.29
>> >> >>
>> >> >> Also 4.6.1 (and 4.6.0) have an issue with IPv6.
>> >> >> https://www.pgpool.net/docs/latest/en/html/release-4-6-2.html
>> >> >>
>> >> >> If possible, I recommend to upgrade to 4.6.2.
>> >> >>
>> >> >> > There is also repmgr running on this 4 node cluster, 1 primary
>> >> >> > and 3 replicas.
>> >> >>
>> >> >> I am not famililar with repmgr, and I ignore this part.
>> >> >>
>> >> >> > All the migration seems to have completed successfully,
>> >> >> > but I've ran into a weird problem with pgpool. I have quite a few
>> >> errors
>> >> >> > that look like the below entries, and it seems to "come and go"
>> when
>> >> >> > checking pgpool log. The process itself, seems to work (I think),
>> but
>> >> >> > every now and then, these errors (warnings?) show up:
>> >> >> >
>> >> >> > 2025-06-01 09:11:00: pid 628043: DEBUG: watchdog heartbeat: send
>> >> >> heartbeat
>> >> >> > signal to db-replica3-priv:9694
>> >> >> > 2025-06-01 09:11:00: pid 628043: LOCATION: wd_heartbeat.c:771
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOG: exit handler called
>> (signal: 2)
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOCATION: pgpool_main.c:1272
>> >> >> >
>> >> >> >
>> >> >> > *2025-06-01 09:11:00: pid 627958: WARNING: failed to lock
>> >> >> > semaphore2025-06-01 09:11:00: pid 627958: DETAIL: Invalid
>> >> >> argument*2025-06-01
>> >> >> > 09:11:00: pid 627958: LOCATION: pool_sema.c:129
>> >> >> > 2025-06-01 09:11:00: pid 627958: WARNING: failed to unlock
>> semaphore
>> >> >> > 2025-06-01 09:11:00: pid 627958: DETAIL: Invalid argument
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOCATION: pool_sema.c:202
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOG: shutting down by signal 2
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOCATION: pgpool_main.c:1324
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOG: terminating all child
>> processes
>> >> >> > 2025-06-01 09:11:00: pid 627958: LOCATION: pgpool_main.c:1334
>> >> >> > 2025-06-01 09:11:00: pid 628047: WARNING: failed to lock semaphore
>> >> >> > 2025-06-01 09:11:00: pid 628047: DETAIL: Invalid argument
>> >> >> > 2025-06-01 09:11:00: pid 628047: LOCATION: pool_sema.c:129
>> >> >> > 2025-06-01 09:11:00: pid 628042: WARNING: failed to lock semaphore
>> >> >> > 2025-06-01 09:11:00: pid 628042: DETAIL: Invalid argument
>> >> >> > 2025-06-01 09:11:00: pid 628042: LOCATION: pool_sema.c:129
>> >> >> > 2025-06-01 09:11:00: pid 628039: WARNING: failed to lock semaphore
>> >> >> > 2025-06-01 09:11:00: pid 628039: DETAIL: Invalid argument
>> >> >>
>> >> >> Can you share the result of "ipcs -s" so that I can confirm pgpool
>> >> >> properly allocates the semaphore.
>> >> >>
>> >> >> By the way do you see "WARNING: failed to unlock semaphore" only when
>> >> >> pgpool is shutting down?
>> >> >>
>> >> >> > Also, earlier in the log, I see errors about being unable to
>> create a
>> >> >> > socket, for some reason it's trying (and failing) to create socket
>> on
>> >> >> > localhost (127.0.0.1:9694) and "creating socket on ::1:9694".
>> Are
>> >> >> these
>> >> >> > "ok to ignore"?
>> >> >>
>> >> >> First of all "creating socket on ::1:9694" looks unusual because it
>> >> >> means that heartbeat_hostname is set to "::1", which is the IPv6 loop
>> >> >> back address. heartbeat_hostname is expected to be set IPv4 or IPv6
>> >> >> inet addesss (not loop back address).
>> >> >>
>> >> >> For now, I would like to wait for your reply regarding these my
>> >> >> questions above.
>> >> >>
>> >> >> Best regards,
>> >> >> --
>> >> >> Tatsuo Ishii
>> >> >> SRA OSS K.K.
>> >> >> English: http://www.sraoss.co.jp/index_en/
>> >> >> Japanese:http://www.sraoss.co.jp
>> >> >>
>> >> >>
>> >> >> > 2025-06-01 09:11:23: pid 634772: DETAIL: creating socket on
>> >> >> 127.0.0.1:9694
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOCATION: wd_heartbeat.c:385
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOG: set SO_REUSEPORT option to
>> the
>> >> >> socket
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOCATION: wd_heartbeat.c:891
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOG: creating watchdog heartbeat
>> >> >> receive
>> >> >> > socket.
>> >> >> > 2025-06-01 09:11:23: pid 634772: DETAIL: creating socket on
>> ::1:9694
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOCATION: wd_heartbeat.c:385
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOG: failed to create watchdog
>> >> >> heartbeat
>> >> >> > receive socket. retrying...
>> >> >> > 2025-06-01 09:11:23: pid 634772: DETAIL: bind failed with reason:
>> >> >> "Cannot
>> >> >> > assign requested address"
>> >> >> > 2025-06-01 09:11:23: pid 634772: LOCATION: wd_heartbeat.c:394
>> >> >> >
>> >> >> >
>> >> >> > 2025-06-01 09:11:22: pid 635274: DEBUG:
>> verify_backend_node_status:
>> >> >> > true_primary 0
>> >> >> > 2025-06-01 09:11:22: pid 635274: LOCATION: pgpool_main.c:2704
>> >> >> > 2025-06-01 09:11:22: pid 635274: DEBUG: node status[0]: 1
>> >> >> > 2025-06-01 09:11:22: pid 635274: LOCATION: pool_worker_child.c:267
>> >> >> > 2025-06-01 09:11:22: pid 635274: DEBUG: node status[1]: 2
>> >> >> > 2025-06-01 09:11:22: pid 635274: LOCATION: pool_worker_child.c:267
>> >> >> > 2025-06-01 09:11:22: pid 635274: DEBUG: node status[2]: 2
>> >> >> > 2025-06-01 09:11:22: pid 635274: LOCATION: pool_worker_child.c:267
>> >> >> > 2025-06-01 09:11:22: pid 635274: DEBUG: node status[3]: 2
>> >> >> > 2025-06-01 09:11:22: pid 635274: LOCATION: pool_worker_child.c:267
>> >> >> > 2025-06-01 09:11:22: pid 635274: DEBUG:
>> >> pool_release_follow_primary_lock
>> >> >> > called
>> >> >> > 2025-06-01 09:11:22: pid 635274: LOCATION: pgpool_main.c:4106
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOG: set SO_REUSEPORT option to
>> the
>> >> >> socket
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOCATION: wd_heartbeat.c:891
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOG: creating watchdog heartbeat
>> >> >> receive
>> >> >> > socket.
>> >> >> > 2025-06-01 09:11:23: pid 634765: DETAIL: creating socket on
>> >> >> 127.0.0.1:9694
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOCATION: wd_heartbeat.c:385
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOG: set SO_REUSEPORT option to
>> the
>> >> >> socket
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOCATION: wd_heartbeat.c:891
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOG: creating watchdog heartbeat
>> >> >> receive
>> >> >> > socket.
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> > *2025-06-01 09:11:23: pid 634765: DETAIL: creating socket on
>> >> >> > ::1:96942025-06-01 09:11:23: pid 634765: LOCATION:
>> >> >> > wd_heartbeat.c:3852025-06-01 09:11:23: pid 634765: LOG: failed to
>> >> >> create
>> >> >> > watchdog heartbeat receive socket. retrying...*2025-06-01 09:11:23:
>> >> pid
>> >> >> > 634765: DETAIL: bind failed with reason: "Cannot assign requested
>> >> >> address"
>> >> >> > 2025-06-01 09:11:23: pid 634765: LOCATION: wd_heartbeat.c:394
>> >> >> > 2025-06-01 09:11:23: pid 634767: LOG: set SO_REUSEPORT option to
>> the
>> >> >> socket
>> >> >> > 2025-06-01 09:11:23: pid 634767: LOCATION: wd_heartbeat.c:891
>> >> >> > 2025-06-01 09:11:23: pid 634767: LOG: creating socket for sending
>> >> >> heartbeat
>> >> >> > 2025-06-01 09:11:23: pid 634767: DETAIL: set SO_REUSEPORT
>> >> >> >
>> >> >> >
>> >> >> > Other odd errors I see in the logs later on are when pgpool tries
>> to
>> >> run
>> >> >> > escalation script - can't quite find where it's failing to find
>> ipv4
>> >> >> > address:
>> >> >> >
>> >> >> > 2025-06-01 00:07:15: pid 395780: LOG: Pgpool-II parent process
>> >> received
>> >> >> > SIGUSR1
>> >> >> > 2025-06-01 00:07:15: pid 395780: LOG: Pgpool-II parent process
>> >> received
>> >> >> > watchdog quorum change signal from watchdog
>> >> >> > 2025-06-01 00:07:15: pid 396973: LOG: watchdog: escalation started
>> >> >> > 2025-06-01 00:07:15: pid 395786: LOG: Setting failover command
>> >> timeout
>> >> >> to
>> >> >> > 135
>> >> >> > 2025-06-01 00:07:15: pid 395780: LOG: watchdog cluster now holds
>> the
>> >> >> quorum
>> >> >> > 2025-06-01 00:07:15: pid 395780: DETAIL: updating the state of
>> >> >> quarantine
>> >> >> > backend nodes
>> >> >> > Sun Jun 1 12:07:15 AM CEST 2025
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> > *escalation.sh: - remove VIP IP from all nodesNode:
>> >> db-primary-privError:
>> >> >> > ipv4: Address not found.Node: db-replica1-privError: ipv4: Address
>> not
>> >> >> > found.Node: db-replica2-privError: ipv4: Address not found.Node:
>> >> >> > db-replica3-privError: ipv4: Address not found.*2025-06-01
>> 00:07:20:
>> >> pid
>> >> >> > 396973: LOG: watchdog escalation successful
>> >> >> > 2025-06-01 00:07:23: pid 396973: LOG: successfully acquired the
>> >> delegate
>> >> >> > IP:"192.168.77.130"
>> >> >> > 2025-06-01 00:07:23: pid 396973: DETAIL: 'if_up_cmd' returned with
>> >> >> success
>> >> >> > 2025-06-01 00:07:23: pid 395786: LOG: watchdog escalation process
>> >> with
>> >> >> > pid: 396973 exit with SUCCESS.
>> >> >> > 2025-06-01 00:07:27: pid 395962: WARNING: failed to lock semaphore
>> >> >> > 2025-06-01 00:07:27: pid 395962: DETAIL: Invalid argument
>> >> >> > 2025-06-01 00:07:27: pid 395962: WARNING: failed to unlock
>> semaphore
>> >> >> > 2025-06-01 00:07:27: pid 395962: DETAIL: Invalid argument
>> >> >> > 2025-06-01 00:07:28: pid 396924: WARNING: failed to lock semaphore
>> >> >> > 2025-06-01 00:07:28: pid 396924: DETAIL: Invalid argument
>> >> >> >
>> >> >> > The way I started was I copied pgpool.conf from the "old" and
>> working
>> >> >> > pgpool 4.2 configuration and modified it slightly, though nothing
>> >> >> > major,changed hostnames and i.e. delegate_ip variable name was
>> changed
>> >> >> > from delegate_IP. Also added this variable as without it, I didn't
>> >> see a
>> >> >> > socket created for port 9898:
>> >> >> > unix_socket_directories = '/var/run/postgresql'
>> >> >> > I had to change network interfaces as well, in the RHEL it was
>> using
>> >> eth0
>> >> >> > where on Ubuntu it's ens18, so I changed lines like:
>> >> >> > /usr/bin/sudo /sbin/ip addr add $_IP_$/23 dev ens18 label ens18:0
>> >> >> > Other thing I had to change was path to arping as on Ubuntu 24
>> it's in
>> >> >> > /usr/bin (not sbin)
>> >> >> > arping_cmd = '/usr/bin/sudo /usr/bin/arping -U $_IP_$ -w 1 -I
>> ens18'
>> >> >> >
>> >> >> > The other thing I'm confused about, I have two network interfaces
>> on
>> >> each
>> >> >> > host, i.e.
>> >> >> > 192.168.77.135/23 brd 192.168.77.255 scope global ens18
>> >> >> > and
>> >> >> > inet 192.168.78.135/24 brd 192.168.78.255 scope global ens19
>> >> >> >
>> >> >> > In pgpool.conf, it is referencing the "priv" hosts (i.e.
>> >> >> > heartbeat_hostname2 = 'db-replica2-priv'), which theoretically
>> should
>> >> be
>> >> >> on
>> >> >> > ens19 network interface as shown above, but in my old pgpool.conf,
>> it
>> >> was
>> >> >> > only referencing eth0 on RHEL, even though "priv" hosts were on
>> eth1.
>> >> >> I'm
>> >> >> > wondering if that needs to be changed in Ubuntu or it makes no
>> >> difference
>> >> >> > here?
>> >> >> >
>> >> >> > Right now, I can't quite figure out whether it is something with
>> >> >> > pgpool.conf or with the Ubuntu settings and the semaphore error is
>> >> quite
>> >> >> > cryptic. If you need me to post some parts of my pgpool.conf,
>> please
>> >> >> > advise which. I've seen an older version of the FAQ that said
>> repmgr
>> >> and
>> >> >> > pgpool don't work together but then I saw mention that this was no
>> >> longer
>> >> >> > the case.
>> >> >> >
>> >> >> > I would much appreciate any help you can provide in solving this
>> >> problem.
>> >> >>
>> >>
>>
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