Обсуждение: Hot-Standby and sequences

Hi All,

I have a question about sequences in combination with streaming replication.
It seems something strange is happening with sequences which are streamed to the slave.

When updating the sequence the last_value on the slave shifts with 32 and halts at this value until the master increased the value also with 32.
Is this normal behavior ?

Please see the example below:

Using Setval
----------------------

# psql -t -h master -c "select setval('foo', 10)"
      10

# psql -t -h master  -c "select last_value from foo"
          10

# psql -t -h slave  -c "select last_value from foo"
          10

Using Nextval
----------------------

# psql -t -h master -c "select nextval('foo')"
       11

# psql -t -h master  -c "select last_value from foo"
          11

# psql -t -h slave -c "select last_value from foo"
         43

-- Wouter D'Haeseleer Linux System Engineer VASCO Data Security Dellingstraat 28b 2800 Mechelen Belgium phone: +32 15 50 44 00 email: wdh@vasco.com web: www.vasco.com

"Wouter D'Haeseleer" <wdh@vasco.com> writes:
> I have a question about sequences in combination with streaming
> replication.
> It seems something strange is happening with sequences which are
> streamed to the slave.

> When updating the sequence the last_value on the slave shifts with 32
> and halts at this value until the master increased the value also with
> 32.
> Is this normal behavior ?

Yes, this is expected because of the hacks that are used to minimize
the number of WAL records emitted during nextval() operations.  The
slave is seeing the state that would prevail on the master, too, if the
master were to crash and restart.

            regards, tom lane

OKay Tom,

Thanks for this clarification