Hello,
After upgrading from (old good no longer supported Pg11) to PostgreSQL 17.5
via pg_dump & pg_restore vacuum started reporting errors:
ERROR: could not map dynamic shared memory segment
Vacuumdb was invoked:
/usr/lib/postgresql/17/bin/vacuumdb -p 5433 -Fvaz -j 12 -v
The vacuum finished exit code was 0, but in PostgreSQL instance log files,
the errors above were logged.
Example error messages from the PostgreSQL log file:
2025-06-21 16:29:56.095 UTC [306130] ERROR: could not map dynamic shared
memory segment
2025-06-21 16:29:56.095 UTC [306131] ERROR: could not map dynamic shared
memory segment
2025-06-21 16:29:56.097 UTC [135978] LOG: background worker "parallel
worker" (PID 306130) exited with exit code 1
2025-06-21 16:29:56.097 UTC [135978] LOG: background worker "parallel
worker" (PID 306131) exited with exit code 1
2025-06-21 16:30:23.677 UTC [300930] postgres@fin LOG: could not send data
to client: Broken pipe
2025-06-21 16:30:23.677 UTC [300930] postgres@fin CONTEXT: while scanning
relation "core.cusip"
2025-06-21 16:30:23.677 UTC [300930] postgres@fin STATEMENT: VACUUM
(SKIP_DATABASE_STATS, FREEZE, VERBOSE) core.cusip;
2025-06-21 16:30:23.677 UTC [300930] postgres@fin FATAL: connection to
client lost
2025-06-21 16:30:23.677 UTC [300930] postgres@fin CONTEXT: while scanning
relation "core.cusip"
2025-06-21 16:30:23.677 UTC [300930] postgres@fin STATEMENT: VACUUM
(SKIP_DATABASE_STATS, FREEZE, VERBOSE) core.cusip;
2025-06-21 16:30:23.678 UTC [306190] ERROR: could not map dynamic shared
memory segment
2025-06-21 16:30:23.680 UTC [135978] LOG: background worker "parallel
worker" (PID 306190) exited with exit code 1
PostgreSQL version:
psql -d postgres -c "select version();"
version
-----------------------------------------------------------------------------------------------------------------------------------
PostgreSQL 17.5 (Ubuntu 17.5-1.pgdg22.04+1) on x86_64-pc-linux-gnu,
compiled by gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0, 64-bit
(1 row)
Configuration parameters:
listen_addresses = '*' # what IP address(es) to listen on;
port = 5432 # (change requires restart)
max_connections = 400 # (change requires restart)
unix_socket_directories = '/var/run/postgresql' # comma-separated list of
directories
tcp_keepalives_idle = 60 # TCP_KEEPIDLE, in seconds;
tcp_keepalives_interval = 5 # TCP_KEEPINTVL, in seconds;
tcp_keepalives_count = 3 # TCP_KEEPCNT;
tcp_user_timeout = 75s # TCP_USER_TIMEOUT, in milliseconds;
client_connection_check_interval = 75s # time between checks for client
shared_buffers = 22GB # min 128kB
huge_pages = on # on, off, or try
temp_buffers = 32MB # min 800kB
work_mem = 64MB # min 64kB
maintenance_work_mem = 2GB # min 64kB
dynamic_shared_memory_type = posix # the default is usually the first option
bgwriter_delay = 10ms # 10-10000ms between rounds
bgwriter_lru_maxpages = 1000 # max buffers written/round, 0 disables
bgwriter_lru_multiplier = 10.0 # 0-10.0 multiplier on buffers scanned/round
max_worker_processes = 24 # (change requires restart)
wal_level = logical # minimal, replica, or logical
wal_log_hints = on # also do full page writes of non-critical updates
checkpoint_timeout = 30min # range 30s-1d
checkpoint_completion_target = 0.8 # checkpoint target duration, 0.0 - 1.0
max_wal_size = 120GB
min_wal_size = 10GB
archive_timeout = 1800 # force a WAL file switch after this
max_wal_senders = 12 # max number of walsender processes
max_replication_slots = 12 # max number of replication slots
wal_sender_timeout = 600s # in milliseconds; 0 disables
track_commit_timestamp = on # collect timestamp of transaction commit
wal_receiver_timeout = 600s # time that receiver waits for
jit = off # allow JIT compilation
log_min_duration_statement = 1000 # -1 is disabled, 0 logs all statements
log_autovacuum_min_duration = 0 # log autovacuum activity;
log_checkpoints = on
track_activity_query_size = 32768 # (change requires restart)
track_io_timing = on
track_functions = all # none, pl, all
idle_in_transaction_session_timeout = 1200000 # in milliseconds, 0 is
disabled
shared_preload_libraries =
'pg_stat_statements,pg_stat_kcache,pg_qualstats,pg_partman_bgw,pg_cron,pg_prewarm'
# (change requires restart)
max_locks_per_transaction = 128 # min 10
OS: Ubuntu 22.04.5 LTS, 16vCPUs, ~123 GB RAM
PostgreSQL apt package: postgresql-17/jammy-pgdg,now 17.5-1.pgdg22.04+1
amd64 [installed]
Memory:
grep -e Mem -e Huge /proc/meminfo
MemTotal: 129804320 kB
MemFree: 2127576 kB
MemAvailable: 100695068 kB
AnonHugePages: 0 kB
ShmemHugePages: 0 kB
FileHugePages: 0 kB
HugePages_Total: 12672
HugePages_Free: 10908
HugePages_Rsvd: 9818
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 25952256 kB
It also happened during the application load test, but I've accidentally
copied a wrong log file, and now the server is decommissioned, so I have no
details on application queries reporting the exact same message, but it
seemed to be related to parallel queries as well if I remember it properly.
The application benefits from parallel queries, so despite the first
temptation to disable parallel queries (based on log entries correlation
only, but is that the root cause?) I did not want to disable parallel
queries, if there is another workaround/solution/fix available.
Thanks for any hints on how to provide more information if needed, as well
as for fix/workaround advice.
Kind regards Ales Zeleny
