The preparation and closing of prepared statements was sent to all servers
even though the execution was always sent to the master. With this change,
all queries which interact with prepared statements are only sent to the master.
The sending of statement preparations to all servers is a problem when a
statement which depends on a database or a table is created and the DDL
statement which created that table has not yet been replicated to the
slaves.
In addition to fixing the aforementioned problem, this change should also
reduce unnecessary network traffic to slaves and improve the overall
performance of the prepared statements.
If individual servers had a weightby parameter value greater than INT_MAX * 1000
the integer used for calculation would overflow and the server would end up
having a negative weight. This would cause all connections to pile up on this
server.
The same overflow was possible for the sum of all the weightby parameter values
even if no single parameter exceeded the limit.
The earlier log file based approach for enabling and disabling
messages has now been completely replaced with the syslog priority
based approach.
Similarly as with log files before it is now possible to enable
and disable a log priority for a particular session, even though
it apparently has not been used much.
The local test-programs of the logging has got minimal attention
only to make them compile. They should get an overhaul as they did
not work before either.
The combination of only one slave being used and the slave_selection_criteria
being LEAST_CURRENT_OPERATIONS can possibly cause a connection pileup on one
slave server. This would skew the query distribution heavily towards the first
available slave even if multiple slave were being used.
Having the maximum number of slave servers to be equal to the total amount of
available slaves allows for a more even and responsive distribution of the
query traffic.
The log manager variables lm_enabled_log_files_bitmask, log_ses_count
and tls_log_info that earlier were declared separately in every
c-file are now declared in the log_manager.h header.
Prepared statements are sent to the master instead of all servers.
The planned functionality to store the types of the prepared statements was not implemented
and all executions of prepared statements are sent to the master. Because of this the preparations
should be all sent to the master server instead of sending them to all servers.
Before these changes when max_sescmd_history was used the session
was closed when the limit was exceeded. With this change, when the
limit is exceeded the recovery of slaves and the session command history
are both disabled. This will allow the sessions to continue while still
keeping the old functionality of limited salve replacement.
The disable_sescmd_history and disable_slave_recovery parameters were combined
so that disabling the session command history will also disable slave recovery.
This way no harm can be done with disable_sescmd_history.
routeQuery calls route_single_stmt, which requires the GWBUF to be
contiguous. Earlier it was made contiguous (if needed) in
route_single_stmt. However, since the process of making a GWBUF
contiguous causes the original buffer to be freed, this would lead
to a double free later in routeQuery that frees the passed buffer.
This is prevented now by making the buffer contiguous before calling
route_single_stmt.
In the end of execute_sescmd_in_backend the buffer was consumed
in case the protocol function failed. Or actually if it returned
something else but 1.
In the case of mysql_backend, the buffer is always freed when
authorizing and either consumed or placed on the dcb writequeue
when the data is written.
That is, it is never ok to consume the buffer in this function.
The end-result is likely to be an abort.
