In order to handle CHAR() fields, 8 bits were reserved for
the size of the CHAR field. However, instead of denoting the
number of characters in the field, field_length was used which
denotes the number of bytes in the field.
Since UTF-8 fields can have three bytes per character (and
has been extended to have four bytes per character in 6.0),
an extra two bits have been encoded in the field metadata
work for fields of type Field_string (i.e., CHAR fields).
Since the metadata word is filled, the extra bits have been
encoded in the upper 4 bits of the real type (the most
significant byte of the metadata word) by computing the
bitwise xor of the extra two bits. Since the upper 4 bits
of the real type always is 1111 for Field_string, this
means that for fields of length <256, the encoding is
identical to the encoding used in pre-5.1.26 servers, but
for lengths of 256 or more, an unrecognized type is formed,
causing an old slave (that does not handle lengths of 256
or more) to stop.
The bug allow multiple executing transactions working with non-transactional
to interfere with each others by interleaving the events of different trans-
actions.
Bug is fixed by writing non-transactional events to the transaction cache and
flushing the cache to the binary log at statement commit. To mimic the behavior
of normal statement-based replication, we flush the transaction cache in row-
based mode when there is no committed statements in the transaction cache,
which means we are committing the first one. This means that it will be written
to the binary log as a "mini-transaction" with just the rows for the statement.
Note that the changes here does not take effect when building the server with
HAVE_TRANSACTIONS set to false, but it is not clear if this was possible before
this patch either.
For row-based logging, we also have that when AUTOCOMMIT=1, the code now always
generates a BEGIN/COMMIT pair for single statements, or BEGIN/ROLLBACK pair in the
case of non-transactional changes in a statement that was rolled back. Note that
for the case where changes to a non-transactional table causes a rollback due
to error, the statement will now be logged with a BEGIN/ROLLBACK pair, even
though some changes has been committed to the non-transactional table.
Problem: in mixed and statement mode, a query that refers to a
system variable will use the slave's value when replayed on
slave. So if the value of a system variable is inserted into a
table, the slave will differ from the master.
Fix: mark statements that refer to a system variable as "unsafe",
meaning they will be replicated by row in mixed mode and produce a warning
in statement mode. There are some exceptions: some variables are actually
replicated. Those should *not* be marked as unsafe.
BUG#34732: mysqlbinlog does not print default values for auto_increment variables
Problem: mysqlbinlog does not print default values for some variables,
including auto_increment_increment and others. So if a client executing
the output of mysqlbinlog has different default values, replication will
be wrong.
Fix: Always print default values for all variables that are replicated.
I need to fix the two bugs at the same time, because the test cases would
fail if I only fixed one of them.
Problem: it is unsafe to read base64-printed events without first
reading the Format_description_log_event (FD). Currently, mysqlbinlog
cannot print the FD.
As a side effect, another bug has also been fixed: When mysqlbinlog
--start-position=X was specified, no ROLLBACK was printed. I changed
this, so that ROLLBACK is always printed.
This patch does several things:
- Format_description_log_event (FD) now print themselves in base64
format.
- mysqlbinlog is now able to print FD events. It has three modes:
--base64-output=auto Print row events in base64 output, and print
FD event. The FD event is printed even if
it is outside the range specified with
--start-position, because it would not be
safe to read row events otherwise. This is
the default.
--base64-output=always Like --base64-output=auto, but also print
base64 output for query events. This is
like the old --base64-output flag, which
is also a shorthand for
--base64-output=always
--base64-output=never Never print base64 output, generate error if
row events occur in binlog. This is
useful to suppress the FD event in binlogs
known not to contain row events (e.g.,
because BINLOG statement is unsafe,
requires root privileges, is not SQL, etc)
- the BINLOG statement now handles FD events correctly, by setting
the thread's rli's relay log's description_event_for_exec to the
loaded event.
In fact, executing a BINLOG statement is almost the same as reading
an event from a relay log. Before my patch, the code for this was
separated (exec_relay_log_event in slave.cc executes events from
the relay log, mysql_client_binlog_statement in sql_binlog.cc
executes BINLOG statements). I needed to augment
mysql_client_binlog_statement to do parts of what
exec_relay_log_event does. Hence, I did a small refactoring and
moved parts of exec_relay_log_event to a new function, which I
named apply_event_and_update_pos. apply_event_and_update_pos is
called both from exec_relay_log_event and from
mysql_client_binlog_statement.
- When a non-FD event is executed in a BINLOG statement, without
previously executing a FD event in a BINLOG statement, it generates
an error, because that's unsafe. I took a new error code for that:
ER_NO_FORMAT_DESCRIPTION_EVENT_BEFORE_BINLOG_STATEMENTS.
In order to get a decent error message containing the name of the
event, I added the class method char*
Log_event::get_type_str(Log_event_type type), which returns a
string name for the given Log_event_type. This is just like the
existing char* Log_event::get_type_str(), except it is a class
method that takes the log event type as parameter.
I also added PRE_GA_*_ROWS_LOG_EVENT to Log_event::get_type_str(),
so that names of old rows event are properly printed.
- When reading an event, I added a check that the event type is known
by the current Format_description_log_event. Without this, it may
crash on bad input (and I was struck by this several times).
- I patched the following test cases, which all contain BINLOG
statements for row events which must be preceded by BINLOG
statements for FD events:
- rpl_bug31076
While I was here, I fixed some small things in log_event.cc:
- replaced hard-coded 4 by EVENT_TYPE_OFFSET in 3 places
- replaced return by DBUG_VOID_RETURN in one place
- The name of the logfile can be '-' to indicate stdin. Before my
patch, the code just checked if the first character is '-'; now it
does a full strcmp(). Probably, all arguments that begin with a -
are already handled somewhere else as flags, but I still think it
is better that the code reflects what it is supposed to do, with as
little dependencies as possible on other parts of the code. If we
one day implement that all command line arguments after -- are
files (as most unix tools do), then we need this.
I also fixed the following in slave.cc:
- next_event() was declared twice, and queue_event was not static but
should be static (not used outside the file).
