** Changed in: postgresql-common (Debian)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/1042556
Title:
Critical data loss bug in postgresql-common initscript
Status in “postgresql-common” package in Ubuntu:
Fix Released
Status in “postgresql-common” source package in Lucid:
In Progress
Status in “postgresql-common” source package in Precise:
Fix Released
Status in “postgresql-common” package in Debian:
Fix Released
Bug description:
Hi
The Debian packages for PostgreSQL (and thus the Ubuntu packages
because of the shared use of pg_wrapper) are subject to a potentially
critical data loss bug because of an unsafe procedure for restarting
PostgreSQL.
This issue has been recognised and patched in Debian:
http://anonscm.debian.org/loggerhead/pkg-postgresql/postgresql-common/trunk/revision/1181
http://archives.postgresql.org/pgsql-general/2012-07/msg00501.php
but should be urgently included in Ubuntu and backported.
I quote Tom Lane (key PostgreSQL dev):
[The] forced unlink on the postmaster.pid file [...] (a) is entirely
unnecessary, and (b) defeats the safety interlock against starting a
new postmaster before all the old backends have flushed out.
It is VITAL that pg_wrapper NEVER unlink the postmaster.pid file. The
postmaster will do that its self if it finds the pid to be stale, but
only after performing some checks to make sure there are no backends
still running and to ensure that there's no other postmaster running
against the database.
See:
http://archives.postgresql.org/pgsql-general/2012-07/msg00475.php
Context here:
http://archives.postgresql.org/pgsql-general/2012-07/msg00350.php
http://dba.stackexchange.com/questions/20959/recover-postgresql-database-from-wal-errors-on-startup/20961
SRU INFORMATION:
* Impact: Severe data loss in rare corner cases.
* Regression potential: Very low. The change has been in Debian,
Quantal, and my very popular PostgreSQL backports repository for quite
some time. pg_ctlcluster has a function start_check_pid_file() which
cleans up a stale PID file on startup if it still exists after
pg_ctlcluster stop --force goes to kill -9 the postmaster, so that
does not stop a subsequent startup. The test suite (t/030_errors.t)
explicitly covers scenarios with missing, broken, and stale PID files
and ensures that they are handled properly.
* Test case: I do not know a realistic and reliable test case to
cause the data loss, but the analysis of the bug in above ML thread is
very clear. I suggest to regression-test the change only, i. e. run
the postgresql-common test suite and a manual check that starting a
cluster still works with a stale pid file being around:
sudo pg_createcluster 9.1 test --start
sudo cp /var/lib/postgresql/9.1/test/postmaster.pid{,.save}
sudo pg_ctlcluster 9.1 test stop
# now cause a stale pid file
sudo cp /var/lib/postgresql/9.1/test/postmaster.pid{.save,}
# this should succeed and say "Removed stale pid file."
sudo pg_ctlcluster 9.1 test start
# this should say that 9.1/test is online
pg_lsclusters
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