[PERFORM] Incr/Decr Integer
Hey all! Is there a better way to increase or decrease the value of an integer than doing something like: --- UPDATE the_table SET the_int = the_int + 1 WHERE the_id = 123 ; --- We seem to be getting a lot of deadlocks using this method under heavy load. Just wondering if we should be doing something different. Thanks! -William -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] VACUUM vs. REINDEX
Hi Jeff, We are running ANALYZE with the hourly VACUUMs. Most of the time the VACUUM for this table looks like this: INFO: vacuuming public.event_sums INFO: index event_sums_event_available now contains 35669 row versions in 1524 pages DETAIL: 22736 index row versions were removed. 1171 index pages have been deleted, 1142 are currently reusable. CPU 0.03s/0.04u sec elapsed 0.06 sec. INFO: index event_sums_date_available now contains 35669 row versions in 3260 pages DETAIL: 22736 index row versions were removed. 1106 index pages have been deleted, 1086 are currently reusable. CPU 0.06s/0.14u sec elapsed 0.20 sec. INFO: index event_sums_price_available now contains 35669 row versions in 2399 pages DETAIL: 22736 index row versions were removed. 16 index pages have been deleted, 16 are currently reusable. CPU 0.05s/0.13u sec elapsed 0.17 sec. INFO: event_sums: removed 22736 row versions in 1175 pages DETAIL: CPU 0.03s/0.05u sec elapsed 0.08 sec. INFO: event_sums: found 22736 removable, 35669 nonremovable row versions in 27866 pages DETAIL: 0 dead row versions cannot be removed yet. There were 767199 unused item pointers. 0 pages are entirely empty. CPU 0.49s/0.45u sec elapsed 0.93 sec. Without any increase in table traffic, every few weeks, things start to look like this: INFO: vacuuming public.event_sums INFO: index event_sums_event_available now contains 56121 row versions in 2256 pages DETAIL: 102936 index row versions were removed. 1777 index pages have been deleted, 1635 are currently reusable. CPU 0.03s/0.16u sec elapsed 1.04 sec. INFO: index event_sums_date_available now contains 56121 row versions in 5504 pages DETAIL: 102936 index row versions were removed. 2267 index pages have been deleted, 2202 are currently reusable. CPU 0.15s/0.25u sec elapsed 13.91 sec. INFO: index event_sums_price_available now contains 56121 row versions in 4929 pages DETAIL: 102936 index row versions were removed. 149 index pages have been deleted, 149 are currently reusable. CPU 0.13s/0.33u sec elapsed 0.51 sec. INFO: event_sums: removed 102936 row versions in 3796 pages DETAIL: CPU 0.31s/0.26u sec elapsed 0.92 sec. INFO: event_sums: found 102936 removable, 35972 nonremovable row versions in 170937 pages DETAIL: 8008 dead row versions cannot be removed yet. There were 4840134 unused item pointers. 0 pages are entirely empty. CPU 5.13s/1.68u sec elapsed 209.38 sec. INFO: analyzing public.event_sums INFO: event_sums: 171629 pages, 3000 rows sampled, 7328 estimated total rows There are a few things in the second vacuum results that catch my eye, but I don't have the skill set to diagnose the problem. I do know, however, that a REINDEX followed by a VACUUM FULL seems to make the symptoms go away for a while. And I agree that we should upgrade to an 8.x version of PG, but as with many things in life time, money, and risk conspire against me. -William At 04:18 PM 7/7/2006, you wrote: On Fri, 7 Jul 2006, William Scott Jordan wrote: Hi all! Can anyone explain to me what VACUUM does that REINDEX doesn't? We have a frequently updated table on Postgres 7.4 on FC3 with about 35000 rows which we VACUUM hourly and VACUUM FULL once per day. It seem like the table still slows to a crawl every few weeks. Running a REINDEX by itself or a VACUUM FULL by itself doesn't seem to help, but running a REINDEX followed immediately by a VACUUM FULL seems to solve the problem. I'm trying to decide now if we need to include a daily REINDEX along with our daily VACUUM FULL, and more importantly I'm just curious to know why we should or shouldn't do that. Any information on this subject would be appreciated. William, If you're having to VACUUM FULL that often, then it's likely your FSM settings are too low. What does the last few lines of VACUUM VERBOSE say? Also, are you running ANALYZE with the vacuums or just running VACUUM? You still need to run ANALYZE to update the planner statistics, otherwise things might slowly grind to a halt. Also, you should probably consider setting up autovacuum and upgrading to 8.0 or 8.1 for better performance overall. -- Jeff Frost, Owner [EMAIL PROTECTED] Frost Consulting, LLC http://www.frostconsultingllc.com/ Phone: 650-780-7908 FAX: 650-649-1954 ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PERFORM] VACUUM vs. REINDEX
Hi Jeff, Ah, okay. I see what information you were looking for. Doing a VACUUM on the full DB, we get the following results: INFO: free space map: 885 relations, 8315 pages stored; 177632 total pages needed DETAIL: Allocated FSM size: 1000 relations + 2 pages = 178 kB shared memory. -William At 05:22 PM 7/7/2006, you wrote: On Fri, 7 Jul 2006, William Scott Jordan wrote: Hi Jeff, We are running ANALYZE with the hourly VACUUMs. Most of the time the VACUUM for this table looks like this: INFO: vacuuming public.event_sums INFO: index event_sums_event_available now contains 56121 row versions in 2256 pages DETAIL: 102936 index row versions were removed. 1777 index pages have been deleted, 1635 are currently reusable. CPU 0.03s/0.16u sec elapsed 1.04 sec. INFO: index event_sums_date_available now contains 56121 row versions in 5504 pages DETAIL: 102936 index row versions were removed. 2267 index pages have been deleted, 2202 are currently reusable. CPU 0.15s/0.25u sec elapsed 13.91 sec. INFO: index event_sums_price_available now contains 56121 row versions in 4929 pages DETAIL: 102936 index row versions were removed. 149 index pages have been deleted, 149 are currently reusable. CPU 0.13s/0.33u sec elapsed 0.51 sec. INFO: event_sums: removed 102936 row versions in 3796 pages DETAIL: CPU 0.31s/0.26u sec elapsed 0.92 sec. INFO: event_sums: found 102936 removable, 35972 nonremovable row versions in 170937 pages DETAIL: 8008 dead row versions cannot be removed yet. There were 4840134 unused item pointers. 0 pages are entirely empty. CPU 5.13s/1.68u sec elapsed 209.38 sec. INFO: analyzing public.event_sums INFO: event_sums: 171629 pages, 3000 rows sampled, 7328 estimated total rows Hmmm..I was looking for something that looks like this: INFO: free space map: 109 relations, 204 pages stored; 1792 total pages needed DETAIL: Allocated FSM size: 1000 relations + 2 pages = 182 kB shared memory. VACUUM Maybe 7.4 doesn't give this? Or maybe you need to run vacuumdb -a -v to get it? There are a few things in the second vacuum results that catch my eye, but I don't have the skill set to diagnose the problem. I do know, however, that a REINDEX followed by a VACUUM FULL seems to make the symptoms go away for a while. And I agree that we should upgrade to an 8.x version of PG, but as with many things in life time, money, and risk conspire against me. You should still be able to use autovacuum, which might make you a little happier. Which 7.4 version are you using? -William At 04:18 PM 7/7/2006, you wrote: On Fri, 7 Jul 2006, William Scott Jordan wrote: Hi all! Can anyone explain to me what VACUUM does that REINDEX doesn't? We have a frequently updated table on Postgres 7.4 on FC3 with about 35000 rows which we VACUUM hourly and VACUUM FULL once per day. It seem like the table still slows to a crawl every few weeks. Running a REINDEX by itself or a VACUUM FULL by itself doesn't seem to help, but running a REINDEX followed immediately by a VACUUM FULL seems to solve the problem. I'm trying to decide now if we need to include a daily REINDEX along with our daily VACUUM FULL, and more importantly I'm just curious to know why we should or shouldn't do that. Any information on this subject would be appreciated. William, If you're having to VACUUM FULL that often, then it's likely your FSM settings are too low. What does the last few lines of VACUUM VERBOSE say? Also, are you running ANALYZE with the vacuums or just running VACUUM? You still need to run ANALYZE to update the planner statistics, otherwise things might slowly grind to a halt. Also, you should probably consider setting up autovacuum and upgrading to 8.0 or 8.1 for better performance overall. -- Jeff Frost, Owner [EMAIL PROTECTED] Frost Consulting, LLC http://www.frostconsultingllc.com/ Phone: 650-780-7908 FAX: 650-649-1954 -- Jeff Frost, Owner [EMAIL PROTECTED] Frost Consulting, LLC http://www.frostconsultingllc.com/ Phone: 650-780-7908 FAX: 650-649-1954 ---(end of broadcast)--- TIP 4: Have you searched our list archives? http://archives.postgresql.org
