It is curious to me that the tuples remaining count varies so wildly. Is this expected?
*Michael Lewis* On Thu, Feb 14, 2019 at 9:09 AM Mariel Cherkassky < mariel.cherkas...@gmail.com> wrote: > I checked in the logs when the autovacuum vacuum my big toasted table > during the week and I wanted to confirm with you what I think : > postgresql-Fri.log:2019-02-08 05:05:53 EST 24776 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 8 > postgresql-Fri.log- pages: 2253 removed, 13737828 remain > postgresql-Fri.log- tuples: 21759258 removed, 27324090 remain > postgresql-Fri.log- buffer usage: 15031267 hits, 21081633 misses, > 19274530 dirtied > postgresql-Fri.log- avg read rate: 2.700 MiB/s, avg write rate: 2.469 > MiB/s > -- > postgresql-Mon.log:2019-02-11 01:11:46 EST 8426 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 23 > postgresql-Mon.log- pages: 0 removed, 23176876 remain > postgresql-Mon.log- tuples: 62269200 removed, 82958 remain > postgresql-Mon.log- buffer usage: 28290538 hits, 46323736 misses, > 38950869 dirtied > postgresql-Mon.log- avg read rate: 2.850 MiB/s, avg write rate: 2.396 > MiB/s > -- > postgresql-Mon.log:2019-02-11 21:43:19 EST 24323 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 1 > postgresql-Mon.log- pages: 0 removed, 23176876 remain > postgresql-Mon.log- tuples: 114573 removed, 57785 remain > postgresql-Mon.log- buffer usage: 15877931 hits, 15972119 misses, > 15626466 dirtied > postgresql-Mon.log- avg read rate: 2.525 MiB/s, avg write rate: 2.470 > MiB/s > -- > postgresql-Sat.log:2019-02-09 04:54:50 EST 1793 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 13 > postgresql-Sat.log- pages: 0 removed, 13737828 remain > postgresql-Sat.log- tuples: 34457593 removed, 15871942 remain > postgresql-Sat.log- buffer usage: 15552642 hits, 26130334 misses, > 22473776 dirtied > postgresql-Sat.log- avg read rate: 2.802 MiB/s, avg write rate: 2.410 > MiB/s > -- > postgresql-Thu.log:2019-02-07 12:08:50 EST 29630 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 13 > postgresql-Thu.log- pages: 0 removed, 10290976 remain > postgresql-Thu.log- tuples: 35357057 removed, 3436237 remain > postgresql-Thu.log- buffer usage: 11854053 hits, 21346342 misses, > 19232835 dirtied > postgresql-Thu.log- avg read rate: 2.705 MiB/s, avg write rate: 2.437 > MiB/s > -- > postgresql-Tue.log:2019-02-12 20:54:44 EST 21464 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 10 > postgresql-Tue.log- pages: 0 removed, 23176876 remain > postgresql-Tue.log- tuples: 26011446 removed, 49426774 remain > postgresql-Tue.log- buffer usage: 21863057 hits, 28668178 misses, > 25472137 dirtied > postgresql-Tue.log- avg read rate: 2.684 MiB/s, avg write rate: 2.385 > MiB/s > -- > > > Lets focus for example on one of the outputs : > postgresql-Fri.log:2019-02-08 05:05:53 EST 24776 LOG: automatic vacuum > of table "myDB.pg_toast.pg_toast_1958391": index scans: 8 > postgresql-Fri.log- pages: 2253 removed, 13737828 remain > postgresql-Fri.log- tuples: 21759258 removed, 27324090 remain > postgresql-Fri.log- buffer usage: *15031267* hits, *21081633 *misses, > *19274530 > *dirtied > postgresql-Fri.log- avg read rate: 2.700 MiB/s, avg write rate: 2.469 > MiB/s > > The cost_limit is set to 200 (default) and the cost_delay is set to 20ms. > The calculation I did : (1**15031267*+10**21081633*+20**19274530)*/200*20/1000 > = 61133.8197 seconds ~ 17H > So autovacuum was laying down for 17h ? I think that I should increase the > cost_limit to max specifically on the toasted table. What do you think ? Am > I wrong here ? > > > בתאריך יום ה׳, 7 בפבר׳ 2019 ב-18:26 מאת Jeff Janes < > jeff.ja...@gmail.com>: > >> On Thu, Feb 7, 2019 at 6:55 AM Mariel Cherkassky < >> mariel.cherkas...@gmail.com> wrote: >> >> I have 3 questions : >>> 1)To what value do you recommend to increase the vacuum cost_limit ? >>> 2000 seems reasonable ? Or maybe its better to leave it as default and >>> assign a specific value for big tables ? >>> >> >> That depends on your IO hardware, and your workload. You wouldn't want >> background vacuum to use so much of your available IO that it starves your >> other processes. >> >> >> >>> 2)When the autovacuum reaches the cost_limit while trying to vacuum a >>> specific table, it wait nap_time seconds and then it continue to work on >>> the same table ? >>> >> >> No, it waits for autovacuum_vacuum_cost_delay before resuming within the >> same table. During this delay, the table is still open and it still holds a >> lock on it, and holds the transaction open, etc. Naptime is entirely >> different, it controls how often the vacuum scheduler checks to see which >> tables need to be vacuumed again. >> >> >> >>> 3)So in case I have a table that keeps growing (not fast because I set >>> the vacuum_scale_factor to 0 and the autovacuum_vacuum_threshold to 10000). >>> If the table keep growing it means I should try to increase the cost right >>> ? Do you see any other option ? >>> >> >> You can use pg_freespacemap to see if the free space is spread evenly >> throughout the table, or clustered together. That might help figure out >> what is going on. And, is it the table itself that is growing, or the >> index on it? >> >> Cheers, >> >> Jeff >> >
