Thread: last_autovacuum & last_autoanalyze showing NULL
Hi, Our production server is running PostgreSQL v8.2.3 on RHEL5. Autovacuum daemon is also running in the server. A brief background on my use case: We heavily use a table for storing of data temporarily inside PostgreSQL functions. Eventually, there will not be any record in the table. Because this table is used heavily, I usually keep tab of this particular table in "pg_stat_user_tables", so that disk space is within control. Recently, I noticed that "last_autovacuum" and "last_autoanalyze" column for this table showing a <NULL> value. My question here is, what condition/scenario would make this column to update to <NULL> value by autovacuum? I can add one more point here, which I remember, that is I performed a TRUNCATE on this table just before. I believe that this is not because of TRUNCATE TABLE? Regards, Gnanam
On 10-08-25 03:30 AM, Gnanakumar wrote: > Hi, > > Our production server is running PostgreSQL v8.2.3 on RHEL5. Autovacuum > daemon is also running in the server. > > A brief background on my use case: We heavily use a table for storing of > data temporarily inside PostgreSQL functions. Eventually, there will not be > any record in the table. Because this table is used heavily, I usually keep > tab of this particular table in "pg_stat_user_tables", so that disk space is > within control. > > Recently, I noticed that "last_autovacuum" and "last_autoanalyze" column for > this table showing a<NULL> value. My question here is, what > condition/scenario would make this column to update to<NULL> value by > autovacuum? I can add one more point here, which I remember, that is I > performed a TRUNCATE on this table just before. I believe that this is not > because of TRUNCATE TABLE? Truncate should not affect those values. Has your Postgres instance crashed or been restarted with immediate mode since the last vacuum? This will cause the autovacuum information to be null. Also, are you sure that autovacuum has processed these tables at least once? -- Brad Nicholson 416-673-4106 Database Administrator, Afilias Canada Corp.
> Truncate should not affect those values. OK. > Has your Postgres instance crashed or been restarted with immediate mode since the last vacuum? This will cause the autovacuum information to be null. No, it's been up and running for almost a week. I even checked with "select pg_postmaster_start_time()". > Also, are you sure that autovacuum has processed these tables at least once? Yes, am very sure about this. As I told earlier, I keep tab on this particular table and even noticed last autovacuum and last autoanalyze every 15 minutes (using cron job I write it to a file) with timestamp before.
"Gnanakumar" <gnanam@zoniac.com> writes:
>> Has your Postgres instance crashed or been restarted with immediate mode
>> since the last vacuum? This will cause the autovacuum information to be
>> null.
> No, it's been up and running for almost a week. I even checked with "select
> pg_postmaster_start_time()".
I don't believe pg_postmaster_start_time() is reset by a
backend-crash-and-restart sequence ... but the stats collector data will
be. You might want to look into the postmaster log for evidence of
such a crash.
regards, tom lane
> I don't believe pg_postmaster_start_time() is reset by a > backend-crash-and-restart sequence ... but the stats collector data will > be. You might want to look into the postmaster log for evidence of > such a crash. I'm sure that the backend has neither restarted nor crashed at that moment. Anyway, I've also confirmed this in the server log, I don't find any evidence or trace of this happened. Is there any other possible reasons that could make autovacuum daemon to update it to NULL value? NOTE: "log_min_messages" is set to NOTICE.