• dlenev@mockturtle.local's avatar
    Fix for: · 8b93e52e
    dlenev@mockturtle.local authored
      Bug #20662 "Infinite loop in CREATE TABLE IF NOT EXISTS ... SELECT
                  with locked tables"
      Bug #20903 "Crash when using CREATE TABLE .. SELECT and triggers"
      Bug #24738 "CREATE TABLE ... SELECT is not isolated properly"
      Bug #24508 "Inconsistent results of CREATE TABLE ... SELECT when
                  temporary table exists"
     
    Deadlock occured when one tried to execute CREATE TABLE IF NOT
    EXISTS ... SELECT statement under LOCK TABLES which held
    read lock on target table.
    Attempt to execute the same statement for already existing
    target table with triggers caused server crashes.
    Also concurrent execution of CREATE TABLE ... SELECT statement
    and other statements involving target table suffered from
    various races (some of which might've led to deadlocks).
    Finally, attempt to execute CREATE TABLE ... SELECT in case
    when a temporary table with same name was already present
    led to the insertion of data into this temporary table and
    creation of empty non-temporary table.
     
    All above problems stemmed from the old implementation of CREATE
    TABLE ... SELECT in which we created, opened and locked target
    table without any special protection in a separate step and not
    with the rest of tables used by this statement.
    This underminded deadlock-avoidance approach used in server
    and created window for races. It also excluded target table
    from prelocking causing problems with trigger execution.
      
    The patch solves these problems by implementing new approach to
    handling of CREATE TABLE ... SELECT for base tables.
    We try to open and lock table to be created at the same time as
    the rest of tables used by this statement. If such table does not
    exist at this moment we create and place in the table cache special
    placeholder for it which prevents its creation or any other usage
    by other threads.
    
    We still use old approach for creation of temporary tables.
    
    Also note that we decided to postpone introduction of some tests
    for concurrent behaviour of CREATE TABLE ... SELECT till 5.1.
    The main reason for this is absence in 5.0 ability to set @@debug
    variable at runtime, which can be circumvented only by using several
    test files with individual .opt files. Since the latter is likely
    to slowdown test-suite unnecessary we chose not to push this tests
    into 5.0, but run them manually for this version and later push
    their optimized version into 5.1
    8b93e52e
create.result 28.2 KB