printf "testing_delay:" > Makefile.bug printf "\tpsql -c 'DROP DATABASE mydb' template1" >> Makefile.bug printf "\tpsql -c 'CREATE DATABASE mydb' template1" >> Makefile.bug
To reproduce and test this bug, issue `make -f Makefile.bug`.
With the following config settings:
# - Background writer - bgwriter_delay = 5000 # 10-5000 milliseconds bgwriter_percent = 1 # 0-100% of dirty buffers bgwriter_maxpages = 1 # 1-1000 buffers max at once
it is *very* easy to reproduce this problem (note, there is a bug in the default config, the min percent is 1, no 0 as the comment suggests). With the default settings, it has been harder to spot on my laptop. I believe that higher end systems with higher values will trip over this problem less frequently.
With the settings set: % make -f Makefile.bug psql -c "DROP DATABASE mydb" template1 DROP DATABASE psql -c "CREATE DATABASE mydb" template1 ERROR: source database "template1" is being accessed by other users *** Error code 1
The problem being, I've disconnected from template1 already, but the database hasn't flushed this to disk so the parent postmaster process isn't aware of the disconnection, so when I connect to the backend again, the newly created child has an inconsistent view of the current connections which prevents me from creating a new database (maybe the old backend is still around cleaning up and really hasn't exited, I'm not sure).
I think the same phenomena used to exist with temp tables across connections that reconnected to a backend with the same backend # (ie, connect to backend 123, create a temp table, disconnect, reconnect and get backend 123, recreate the same temp table and you'll get an error... though I can't reproduce the temp table error right now, yay!).
Anyway, Tom/Jan, this code seems to be your areas of expertise, could either of you take a look? -sc
-- Sean Chittenden
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