BUG #18954: Error "could not reserve shared memory region ... error code 487" on Windows

The following bug has been logged on the website:

Bug reference: 18954
Logged by: Seva Zaslavsky
Email address: szaslavsky(at)mpcapitallp(dot)com
PostgreSQL version: 17.5
Operating system: Windows Server 2019, Windows 11
Description:

In PG 17.5 on Windows, I'm seeing errors in the log that look like:
2025-06-10 12:53:44.548 EDT [18612] LOG: could not reserve shared memory
region (addr=0000022916760000) for child 00000000000014C4: error code 487
2025-06-10 13:09:44.667 EDT [18612] LOG: could not reserve shared memory
region (addr=0000022916760000) for child 00000000000014A8: error code 487
2025-06-10 13:14:44.797 EDT [18612] LOG: could not reserve shared memory
region (addr=0000022916760000) for child 00000000000014CC: error code 487
I was able to duplicate the issue fairly easily in two unconnected/unrelated
environments. The issue appears to be triggered/exacerbated by higher
settings of shared_buffers in postgresql.conf
Steps to replicate:
1. Install PG 17.5 on a windows machine from the EDB community release
https://www.enterprisedb.com/downloads/postgres-postgresql-downloads
2. In the default postgresql.conf that is created by the installer,
change shared_buffers as follows: On an 8GB laptop (windows 11), I changed
shared_buffers to 3GB. On a 768 GB Dell server (Windows Server 2019),
changing shared_buffers to 256GB showed the error message quite often but
with shared_buffers=128GB it took a couple of minutes for the message to
appear. Sometimes the messages appears right away during startup, other
times it can take a while.
Start the cluster with pg_ctl and watch the output. The higher the
setting of shared_buffers, the more frequent the messages appear. On the 8
GB laptop, it took over 30 minutes to see the first message. On the Dell
server I was getting those messages sometimes even before the server was
ready to accept connections.
Notes:
1. the same hardware and Operating system runs PG 13.18 without those
error messages.
2. There are no active connections or queries running during my testing
I set the logging to Debug5 and here are some associated messages. PID 19048
is the postmaster, not sure what PID 14992 is doing:
2025-06-10 10:11:47.402 EDT [14992] [] DEBUG: StartTransaction(1) name:
unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
2025-06-10 10:11:47.402 EDT [14992] [] DEBUG: CommitTransaction(1) name:
unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 0/1/0
2025-06-10 10:11:47.402 EDT [19048] [] DEBUG: postmaster received pmsignal
signal
2025-06-10 10:11:47.402 EDT [19048] [] DEBUG: mapped win32 error code 2 to
2
2025-06-10 10:11:47.403 EDT [19048] [] DEBUG: mapped win32 error code 2 to
2
2025-06-10 10:11:47.406 EDT [19048] [] LOG: could not reserve shared memory
region (addr=000001A228F90000) for child 0000000000002168: error code 487
Related DBA StackExchange post:
https://dba.stackexchange.com/questions/346875/error-could-not-reserve-shared-memory-region-error-code-487-on-postgresql