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Re: [Merge] lp:~paul-mccullagh/maria/pbxt-1.0.11 into lp:maria
Thanks for clearing this up.
The problem is certainly as you say: it depends on the speed of a
From this point of view the test does not make all that much sense
for PBXT which returns inconsistent row count estimates.
I think I will adjust the test to work in all cases with PBXT.
On May 10, 2010, at 4:57 PM, Kristian Nielsen wrote:
Paul McCullagh <paul.mccullagh@xxxxxxxxxxxxx> writes:
All tests in the PBXT suite run through on Mac and Linux, except
for one error under Linux, which is a bit weird (see below).
pbxt.select_safe [ fail ]
Test ended at 2010-05-06 17:19:13
mysqltest: At line 19: query 'select 1 from t1,t1 as t2,t1 as t3'
failed: 1104: The SELECT would examine more than MAX_JOIN_SIZE
rows; check your WHERE and use SET SQL_BIG_SELECTS=1 or SET
SQL_MAX_JOIN_SIZE=# if the SELECT is okay
The result from queries just before the failure was:
drop table if exists t1;
SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=4, SQL_MAX_JOIN_SIZE=9;
create table t1 (a int auto_increment primary key, b char(20));
insert into t1 values(1,"test");
SELECT SQL_BUFFER_RESULT * from t1;
update t1 set b="a" whe
Ok, I looked into this.
So this test does a three-way cartesian self-join on a table with 2
total of 8 rows). And it sets SQL_MAX_JOIN_SIZE=9. And sometimes
timing dependent), this test fails because the optimiser estimates
more than 9
rows in the join. So the problem here is that the optimiser estimate
sometimes too big for SQL_MAX_JOIN_SIZE=9.
What I found is that when the test case fails, the function
returns records==3 for the table. When the test case succeeds, it
records==2. So it's pretty clear that the server will throw an error
records==3 and SQL_MAX_JOIN_SIZE=9.
What remains to consider is why the returned records value differs
The testcase actually first inserts a row, then deletes it, then
more rows. I'm speculating that PBXT has some background cleanup
similar that causes a race between freeing up space from the first
allocating space for the two new rows?
So Paul, do you think returning records = 2 or 3 at random from
ha_pbxt::info() is expected or not?
If expected, one way to fix the problem is to create a new table
running the test:
create table t2 like t1;
insert into t2 select * from t1;
analyze table t2; # PBXT: required to get the correct COUNT(*)
select 1 from t2 as t1,t2,t2 as t3;
Then there is no possibility for the insert+delete to take up a slot
a failure (I was not able to repeat the failure with this change).
Alternatively, we can just increate the SQL_MAX_JOIN_SIZE value.
Or alternatively, you may decide that the test is meaningless for
PBXT due to
imprecise statistics, and just remove it from select_safe.test.
Just let me know what you prefer, and I'll change it as needed.