Re: very slow queries and ineffective vacuum

William Dunn <dunnwjr(at)gmail(dot)com> writes:

> Sorry I meant to say, "To track transactions that have been left idle but not committed or rolled back you would..."
> Typo

foodb/postgres
=# \d pg_stat_activity|pg_prepared_xacts
View "pg_catalog.pg_prepared_xacts"
Column | Type | Modifiers
-------------+--------------------------+-----------
transaction | xid |
gid | text |
prepared | timestamp with time zone |
owner | name |
database | name |

View "pg_catalog.pg_stat_activity"
Column | Type | Modifiers
------------------+--------------------------+-----------
datid | oid |
datname | name |
pid | integer |
usesysid | oid |
usename | name |
application_name | text |
client_addr | inet |
client_hostname | text |
client_port | integer |
backend_start | timestamp with time zone |
xact_start | timestamp with time zone |
query_start | timestamp with time zone |
state_change | timestamp with time zone |
waiting | boolean |
state | text |
query | text |

foodb/postgres
=#

>
> Will J. Dunn
> willjdunn.com
>
> On Tue, Jun 30, 2015 at 4:33 PM, William Dunn <dunnwjr(at)gmail(dot)com> wrote:
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
> Perhaps I'm missing some indexes on the tables (creating them on the columns on which the where clause was used in the long queries seemed to halve their
> times). Also how can I monitor my transactions and if they are closed properly?
>
> To track transactions that have not been left idle but not committed or rolled back you would:
>
> 1) Set track_activities true in the config (doc: http://www.postgresql.org/docs/current/static/runtime-config-statistics.html#GUC-TRACK-ACTIVITIES)
> 2) Query the pg_stat_activity view for connections where state = 'idle in transaction' (doc: http://www.postgresql.org/docs/current/static/monitoring-stats.html#
> PG-STAT-ACTIVITY-VIEW)
>
> As you would suspect, transactions that have been left "idle in transaction" prevent vacuum from removing old tuples (because they are still in scope for that
> transaction)
>
> Will J. Dunn
> willjdunn.com
>
> On Tue, Jun 30, 2015 at 4:27 PM, William Dunn <dunnwjr(at)gmail(dot)com> wrote:
>
> Hello Lukasz,
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
> There doesn't seem to be any issues with disk space, memory or CPU, as neither of those is even 50% used (as per df and top).
>
> Are you using the default PostgreSQL configuration settings, or have you custom tuned them? The default settings are targeted for wide compatibility and are not
> optimized for performance. If PostgreSQL is performing badly and using a small amount of system resources it is likely some tuning is needed. See docs: http://
> www.postgresql.org/docs/current/static/runtime-config.html 
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
> For whatever reason there is also no data in pg_stat* tables.
>
> You can also turn on tracking (for statistics views) by enabling statistics collection in the config http://www.postgresql.org/docs/current/static/
> runtime-config-statistics.html
>
> Will J. Dunn
> willjdunn.com
>
> On Tue, Jun 30, 2015 at 8:57 AM, Lukasz Wrobel <lukasz(dot)wrobel(at)motorolasolutions(dot)com> wrote:
>
> Hello.
>
> I have multiple problems with my database, the biggest of which is how to find out what is actually wrong.
>
> First of all I have a 9.3 postgres database that is running for about a month. Right now the queries on that database are running very slowly (select with a
> simple "where" on a non-indexed column on a table with about 5000 records takes 1,5s, a complicated hibernate select with 7 joins on tables of about 5000
> records takes about 15s, insert or update on a table with 35000 records takes up to 20 mins).
>
> The tables and indexes on those tables are bloated to the point where this query: https://wiki.postgresql.org/wiki/Show_database_bloat shows wasted bytes in
> hundreds of MB.
>
> For whatever reason there is also no data in pg_stat* tables.
>
> So due to the long query times, there are multiple errors in my application logs like "No free connection available" or "Could not synchronize database
> state with session", or "Failed to rollback transaction" and the application fails to start in the required time.
>
> The only thing that helps fix the situation seems to be vacuum full of the entire database. Regular vacuum doesn't even lower the dead tuples count (which
> appear by the thousands during application launching). Reindex of all the indexes in the database didn't help as well. All autovacuum parameters are
> default.
>
> There doesn't seem to be any issues with disk space, memory or CPU, as neither of those is even 50% used (as per df and top).
>
> Is there any good tool that will monitor the queries and generate a report with useful information on what might be the problem? I tried pg_badger, but all
> I got were specific queries and their times, but the long query times are just one of the symptoms of what's wrong with the database, not the cause.
>
> Perhaps I'm missing some indexes on the tables (creating them on the columns on which the where clause was used in the long queries seemed to halve their
> times). Also how can I monitor my transactions and if they are closed properly?
>
> I will be grateful for any help and if you need more details I can provide them if possible.
>
> Best regards.
> Lukasz
>

--
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres(dot)consulting(at)comcast(dot)net
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