Problem description:
Table 't' created with two colums having compound index on both the
columns under innodb/myisam engine at remote machine. In the local
machine same table is created undet the federated engine.
A select having where clause with along 'AND' operation gives wrong
results on local machine.
Analysis:
The given query at federated engine is wrongly transformed by
federated::create_where_from_key() function and the same was sent to
the remote machine. Hence the local machine is showing wrong results.
Given query "select c1 from t where c1 <= 2 and c2 = 1;"
Query transformed, after ha_federated::create_where_from_key() function is:
SELECT `c1`, `c2` FROM `t` WHERE (`c1` IS NOT NULL ) AND
( (`c1` >= 2) AND (`c2` <= 1) ) and the same sent to real_query().
In the above the '<=' and '=' conditions were transformed to '>=' and
'<=' respectively.
ha_federated::create_where_from_key() function behaving as below:
The key_range is having both the start_key and end_key. The start_key
is used to get "(`c1` IS NOT NULL )" part of the where clause, this
transformation is correct. The end_key is used to get "( (`c1` >= 2)
AND (`c2` <= 1) )", which is wrong, here the given conditions('<=' and '=')
are changed as wrong conditions('>=' and '<=').
The end_key is having {key = 0x39fa6d0 "", length = 10, keypart_map = 3,
flag = HA_READ_AFTER_KEY}
The store_length is having value '5'. Based on store_length and length
values the condition values is applied in HA_READ_AFTER_KEY switch case.
The switch case 'HA_READ_AFTER_KEY' is applicable to only the last part of
the end_key and for previous parts it is going to 'HA_READ_KEY_OR_NEXT' case,
here the '>=' is getting added as a condition instead of '<='.
Fix:
Updated the 'if' condition in 'HA_READ_AFTER_KEY' case to affect for all
parts of the end_key. i.e 'i > 0' will used for end_key, Hence added it in
the if condition.
The original goal of the test, as reported on BUG #25721, is to check whether
a deadlock happens or not when concurrently CREATING/ALTERING/DROPPING the
same server. For that a procedure (p1) is created that runs the exact same
CREATE/ALTER/DROP statements for 10K iterations and two different connections
(threads - t1 and t2) call p1 concurrently. At the end of the 10K iterations,
the test checks if there was errors while running the loop (SELECT e >0).
The problem is that In some cases it may happen that one thread, t1, gets
scheduled to execute with just enough time to complete the iteration and
never bumps into the other thread t2. Meaning that t1 will never run into an
SQL exception. On the other hand, the other thread, t2, may run into t1 and
never issue any/part of its own statements because it will throw an SQLEXCEPTION.
This is probably the case for failures where only one value differs.
Furthermore, there is a third scenario: both threads are scheduled to run
interleaved for each iteration (or even one thread completes all iterations
before the other starts). In this case, both will succeed without any error.
This is probably the case for the failure that reports two different values.
This patch addresses the failure in pushbuild by removing the error counting
and the printout (SELECT > 0) at the end of the test. A timeout should occur
if the error that the test is checking surfaces.
