Re: Select max(id) causes AccessExclusiveLock?

Em 28/04/2014 12:01, Tom Lane escreveu:
> Edson Richter <edsonrichter(at)hotmail(dot)com> writes:
>> When I issue a
>> select max(id) from MyTableName
>> Postgres 9.2.7 is scaling a AccessExclusiveLock and causing large delays.
> Really?
>
> regression=# create table MyTableName (
> regression(# id integer not null primary key,
> regression(# seqYear char(4),
> regression(# seqCount integer);
> NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "mytablename_pkey" for table "mytablename"
> CREATE TABLE
> regression=# begin;
> BEGIN
> regression=# select max(id) from MyTableName;
> max
> -----
>
> (1 row)
>
> regression=# select * from pg_locks;
> locktype | database | relation | page | tuple | virtualxid | transactionid | classid | objid | objsubid | virtualtransaction | pid | mode | granted | fastpath
> ------------+----------+----------+------+-------+------------+---------------+---------+-------+----------+--------------------+-------+-----------------+---------+----------
> relation | 16384 | 11069 | | | | | | | | 2/120853 | 12432 | AccessShareLock | t | t
> relation | 16384 | 42142 | | | | | | | | 2/120853 | 12432 | AccessShareLock | t | t
> relation | 16384 | 42139 | | | | | | | | 2/120853 | 12432 | AccessShareLock | t | t
> virtualxid | | | | | 2/120853 | | | | | 2/120853 | 12432 | ExclusiveLock | t | t
> (4 rows)
>
> I see nothing higher than AccessShareLock on the table.
>
> regards, tom lane
>
>

Really big sorry!!!

The programmer added a

LOCK TABLE MyTableName

just before issuing the select max(id) from MyTableName.

I do suspect this is the case, right?

Really sorry, I should have look into the code before asking!

Thanks for your (always) fast support.

Regards,

Edson