Обсуждение: number and type of locks for an alter sequence
Hello ,
In PG10, when I am altering a sequence, i see 2 locks in pg_locks matching my sequence:
a RowExclusiveLock
and a ShareRowExclusiveLock
My question is Why 2 locks?
Someone on irc said it was for catalog but i am no sure because pg_locks.relationid is the same for the 2 locks.
At the same time, If I am trying to call nextval with an othersession, the session wants to get a RowExclusiveLock on the sequence.
So, to me, the lock ShareRowExclusiveLock is when the sequence is beeing altered.
And the RowExclusiveLock is for concurent access between alter/drop sequence and nextval/setval/curval/lastval.
Documentation seems not talking about this... (https://www.postgresql.org/docs/10/explicit-locking.html) Maybe should I open a ticket?
Thanks
On 1/28/19 6:07 AM, Thomas Poty wrote: > Hello , > > In PG10, when I am altering a sequence, i see 2 locks in pg_locks > matching my sequence: > a RowExclusiveLock > and a ShareRowExclusiveLock > > My question is Why 2 locks? > Someone on irc said it was for catalog but i am no sure because > pg_locks.relationid is the same for the 2 locks. > > At the same time, If I am trying to call nextval with an othersession, > the session wants to get a RowExclusiveLock on the sequence. > > So, to me, the lock ShareRowExclusiveLock is when the sequence is beeing > altered. > And the RowExclusiveLock is for concurent access between alter/drop > sequence and nextval/setval/curval/lastval. > > Documentation seems not talking about this... > (https://www.postgresql.org/docs/10/explicit-locking.html) Maybe should > I open a ticket? A sequence, for practical purposes, is a table. So in the above substitute TABLE with SEQUENCE: > > Thanks -- Adrian Klaver adrian.klaver@aklaver.com