On 07/03/2015 03:14 AM, Fabio Pardi wrote:
Hi,
while experimenting with number of locks, i found something I cannot
understand.
From what i can read in the documentation, at any one given time, a
query can obtain a max number of locks given by
max_locks_per_transaction * (max_connections + max_prepared_transactions)
I then changed my db to use this settings:
mydb=# show max_locks_per_transaction ;
max_locks_per_transaction
---------------------------
20
(1 row)
mydb=# show max_connections ;
max_connections
-----------------
2
(1 row)
mydb=# show max_prepared_transactions ;
max_prepared_transactions
---------------------------
0
(1 row)
so i expected to be able to acquire a maximum of 40 locks.
On tables. To continue the docs from where you left off above:
http://www.postgresql.org/docs/9.4/static/runtime-config-locks.html
"The shared lock table tracks locks on max_locks_per_transaction *
(max_connections + max_prepared_transactions) objects (e.g., tables);
hence, no more than this many distinct objects can be locked at any one
time. This parameter controls the average number of object locks
allocated for each transaction; individual transactions can lock more
objects as long as the locks of all transactions fit in the lock table.
This is not the number of rows that can be locked; that value is
unlimited. ..."
Then:
mydb=# begin transaction ;
BEGIN
portavita=# SELECT 1 FROM root.ac;
?column?
----------
(0 rows)
mydb=# select count(*) from pg_locks ;
count
-------
132
(1 row)
Why can I acquire 132 locks while the expected number is 40? What am I
doing wrong?
Take a look here:
http://www.postgresql.org/docs/9.4/interactive/view-pg-locks.html
and see whet the locks are actually being held on.
I m running Postgres 9.2.6
Thanks for your time,
Fabio
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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