Re: assymetry updating a boolean (=FALSE faster than =TRUE)

"George Pavlov" <gpavlov@mynewplace.com> writes:
> Here is something that seems anomalous to me: when I set a boolean field
> to FALSE performance is much better than when I set it to TRUE. Any
> reason for FALSE to be favored over TRUE?

It isn't.  You're measuring something else than you think you're
measuring ... maybe a partial index?  Varying effects of where the
free space is in the table?  In a test case I see no significant
difference:

regression=# create table foo(f1 int, f2 bool);
CREATE TABLE
regression=# insert into foo select x, true from generate_series(1,100000) x;
INSERT 0 100000
regression=# \timing
Timing is on.
regression=# vacuum foo;
VACUUM
Time: 318.153 ms
regression=# update foo set f2 = true;
UPDATE 100000
Time: 2553.014 ms
regression=# vacuum foo;
VACUUM
Time: 410.356 ms
regression=# update foo set f2 = false;
UPDATE 100000
Time: 2453.620 ms
regression=# vacuum foo;
VACUUM
Time: 405.955 ms
regression=# update foo set f2 = true;
UPDATE 100000
Time: 2497.413 ms
regression=# vacuum foo;
VACUUM
Time: 408.403 ms
regression=# update foo set f2 = false;
UPDATE 100000
Time: 2458.824 ms
regression=#

            regards, tom lane