Hi, I revised the patch against HEAD, it's available at: http://people.freebsd.org/~iwasaki/postgres/buffer-cache-hibernation-postgresql-20110506.patch
Implemented hibernation file validations: - comparison with pg_control At shutdown: pg_control state should be DB_SHUTDOWNED. At startup: pg_control state should be DB_SHUTDOWNED. hibernation files should be newer than pg_control. - CRC check At shutdown: compute CRC values for hibernation files and store them into a file. At startup: CRC values for hibernation files should be the same with read from the file created at shutdown. - file size At startup: The size of hibernation file should be the same with calculated file size based on shared_buffers. - buffer descriptors validation At startup: The descriptor flags should not include BM_DIRTY, BM_IO_IN_PROGRESS, BM_IO_ERROR, BM_JUST_DIRTIED and BM_PIN_COUNT_WAITER. Sanity checks for usage_count and usage_count should be done. (wait_backend_pid is zero-cleared because the process was terminated already) - system call error checking At shutdown and startup: Evaluation for return value system call (eg. open(), read(), write() and etc) should be done. > > How do you protect against the cached buffers getting out-of-sync with > > the actual disk files (especially during recovery scenarios)? What > > Saving DB buffer cahce is called at shutdown after finishing > bgwriter's final checkpoint process, so dirty-buffers should not exist > I believe. > For recovery scenarios, I need to research it though... > Could you describe what is need to be consider? I think hibernation should be allowed only when the system is shutdown normaly by checking pg_control state. And once the abnormal shutdown was detected, the hibernation files should be ignored. The latest patch includes this. # modifications for xlog.c:ReadControlFile() was required though... > > about crash-induced corruption in the cache file itself (consider the > > not-unlikely possibility that init will kill the database before it's > > had time to dump all the buffers during a system shutdown)? Do you have > > I think this is important point. I'll implement validation function for > hibernation file. Added validations seem enough for me. # because my understanding on postgres is not enough ;) If any other considerations are required, please point them out. Thanks -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
