Обсуждение: n_live_tup number double after migration do PG 10.4

Hi all,

After the migration to pg 10 by pg_upgrade and vacuumdb, I’ve seen the number of live tuple double and performance
decreaseson few queries. 
Where do these live tuples coming from ?

Thank you

Keith <keith@keithf4.com> writes:
> On Sun, Aug 5, 2018 at 5:29 AM, Mai Peng <maily.peng@webedia-group.com>
> wrote:
>> After the migration to pg 10 by pg_upgrade and vacuumdb, I’ve seen the
>> number of live tuple double and performance decreases on few queries.

> The value stored in n_liv_tup is the value seen when the last analyze was
> run on the table.

No, you're confusing this with pg_class.reltuples.  I think the OP is
talking about pg_stat counters such as pg_stat_all_tables.n_live_tup.
Those should update after every transaction, although there are various
reasons why they might be inaccurate.

The OP hasn't given us nearly enough information to speculate usefully
on what he's seeing.  I'd suggest reading

https://wiki.postgresql.org/wiki/Guide_to_reporting_problems

            regards, tom lane

Hi,
The query I’m talking about is
SELECT schemaname, relname, sum(n_live_tup) AS n_live_tup, sum(n_dead_tup) AS n_dead_tup
  FROM pg_stat_user_tables
  GROUP BY schemaname, relname
  ORDER BY n_live_tup DESC;


> Le 6 août 2018 à 06:24, Tom Lane <tgl@sss.pgh.pa.us> a écrit :
>
> Keith <keith@keithf4.com> writes:
>> On Sun, Aug 5, 2018 at 5:29 AM, Mai Peng <maily.peng@webedia-group.com>
>> wrote:
>>> After the migration to pg 10 by pg_upgrade and vacuumdb, I’ve seen the
>>> number of live tuple double and performance decreases on few queries.
>
>> The value stored in n_liv_tup is the value seen when the last analyze was
>> run on the table.
>
> No, you're confusing this with pg_class.reltuples.  I think the OP is
> talking about pg_stat counters such as pg_stat_all_tables.n_live_tup.
> Those should update after every transaction, although there are various
> reasons why they might be inaccurate.
>
> The OP hasn't given us nearly enough information to speculate usefully
> on what he's seeing.  I'd suggest reading
>
> https://wiki.postgresql.org/wiki/Guide_to_reporting_problems
>
>             regards, tom lane