'conc_sys' test
Concurrent execution of SELECT involing at least two INFORMATION_SCHEMA
tables, DROP DATABASE statement and DROP TABLE statement could have
resulted in stalled connection for this SELECT statement.
The problem was that for the first query of a join there was a race
between select from I_S.TABLES and DROP DATABASE, and the error (no
such database) was prepared to be send to the client, but the join
processing was continued. On second query to I_S.COLUMNS there was a
race with DROP TABLE, but this error (no such table) was downgraded to
warning, and thd->net.report_error was reset. And so neither result
nor error was sent to the client.
The solution is to stop join processing once it is clear we are going
to report a error, and also to downgrade to warnings file system errors
like 'no such database' (unless we are in the 'SHOW' command), because
I_S is designed not to use locks and the query to I_S should not abort
if something is dropped in the middle.
No test case is provided since this bug is a result of a race, and is
timing dependant. But we test that plain SHOW TABLES and SHOW COLUMNS
give a error if there is no such database or a table respectively.
mysql-test/r/show_check.result:
Add result for the test that SHOW TABLES and SHOW COLUMNS give a error
if there is no such database or a table respectively.
mysql-test/t/show_check.test:
Add test case that SHOW TABLES and SHOW COLUMNS give a error
if there is no such database or a table respectively.
sql/mysql_priv.h:
Remove prototype of mysql_find_files(), which is made static under
find_files() name.
sql/sql_show.cc:
Rename mysql_find_files() to find_files() and make it static.
Return FIND_FILES_OK for success, FIND_FILES_OOM for out of memory,
and FIND_FILES_DIR for directory reading error.
Downgrade error to warning in get_all_tables() if it is a
FIND_FILES_DIR error, and we are not in the 'SHOW' command.
Once 'result' is set to 1 in get_schema_tables_result(), there's no
need in continuing iterations, as we are about to return a error.
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