> 10 авг. 2017 г., в 15:09, Chris Travers <chris.trav...@gmail.com> написал(а):
> I ran into a funny situation today regarding PostgreSQL replication and wal
> corruption and wanted to go over what I think happened and what I wonder
> about as a possible solution.
> Basic information is custom-build PostgreSQL 9.6.3 on Gentoo, on a ~5TB
> database with variable load. Master database has two slaves and generates
> 10-20MB of WAL traffic a second. The data_checksum option is off.
> The problem occurred when I attempted to restart the service on the slave
> using pg_ctl (I believe the service had been started with sys V init
> scripts). On trying to restart, it gave me a nice "Invalid memory allocation
> request" error and promptly stopped.
> The main logs showed a lot of messages like before the restart:
> 2017-08-02 11:47:33 UTC LOG: PID 19033 in cancel request did not match any
> 2017-08-02 11:47:33 UTC LOG: PID 19032 in cancel request did not match any
> 2017-08-02 11:47:33 UTC LOG: PID 19024 in cancel request did not match any
> 2017-08-02 11:47:33 UTC LOG: PID 19034 in cancel request did not match any
> On restart, the following was logged to stderr:
> LOG: entering standby mode
> LOG: redo starts at 1E39C/8B77B458
> LOG: consistent recovery state reached at 1E39C/E1117FF8
> FATAL: invalid memory alloc request size 3456458752
> LOG: startup process (PID 18167) exited with exit code 1
> LOG: terminating any other active server processes
> LOG: database system is shut down
> After some troubleshooting I found that the wal segment had become corrupt, I
> copied the correct one from the master and everything came up to present.
> So It seems like somewhere something crashed big time on the back-end and
> when we tried to restart, the wal ended in an invalid way.
We have reported the same thing  nearly a year ago. Could you please check
with pg_xlogdump that both WALs (normal from master and corrupted) are exactly
the same until some certain LSN?
> I am wondering what can be done to prevent these sorts of things from
> happening in the future if, for example, a replica dies in the middle of a
> wal fsync.
> Best Wishes,
> Chris Travers
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May the force be with you…