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One can have data loss in multi-master setups when 1) both masters
update the same table, 2) ALTER TABLE is run on one master which
re-arranges the column ordering, and 3) transactions are binlogged
in ROW binlog_format.
This is because the slave assumes that all columns are in the same
order on the master and slave and all columns on the master also
exists on the slave. This happens even if binlog_row_metadata=FULL is
used. If this is not the case, this will lead to silent data loss.
A new option for slave_type_conversions bit field,
ERROR_IF_MISSING_FIELD, has been added. This allows the user to define if
the slave should abort replication if it is missing some field that
existed on the master. This option is off by default to keep things
compatible with earlier versions.
If a field is missing on the slave and log_warnings >= 1, a warning
will be logged to the error log.
This patch fixes this, when binlog_row_metadata=FULL is used on the
master, by mapping fields with identical names on the master and slave.
If slave has fields that does not exist in the row event, these will
be set to their default value.
The main idea is that we added two conversion tables:
m_tabledef.master_to_slave_map[master_column_index] -> slave_column_index
and m_tabledef.master_to_slave_error[master_column_index] which contains
an error number if the master_column does not exists on the slave or
it is not possible to convert the master data to the slave column.
master_to_slave_error[#] contains 0 if the column exists and is compatible.
General code changes:
- Instead of looping over row fields in the order of slave table
we are instead looping over fields in the order of the binary log.
- We are using table->write_set to know which fields should be updated
on the slave. This is reflected in unpack_row
- We are calling TABLE::mark_columns_per_binlog_row_image() to ensure
that rpl_write_set is properly set. This is needed if the slave also
is doing binary logging.
- Before replication aborted if the master and slave tables where too
different. Now replication is only aborted if the row actually uses
columns that does not exists on the slave (and ALLOW_MISSING_FIELDS
is not used) or uses columns that cannot be converted.
- Instead of giving errors in compatible_with(), used when table is
accessed by first the row event, we are instead giving errors
when we examine a row event and notice that it is accessing
a not existing or not compatible field.
Other code changes:
- Removed conv_table argument from compatible_with() and store it
directly in RPL_TABLE_LIST->m_conv_table
- table_def::compatible_with() returns now 1 on error (not 0).
- Remove m_width and skip arguments from prepare_record() as we are
now using table->write_set() to check which elements need a default
value.
- Moved DBUG_ENTER() to it's proper place (after variable
declarations) in a few functions.
- Some changes in unpack_row():
- Replaced null_mask and null_ptr with an indexed bit check for
simplicity.
- Removed check of rgi == null and table_found which never worked.
- Updated comments to reflect current code.
- Indentation changes as the code now uses 'continue' instead of
'if-else' in the main loop.
- The code to throw away 'extra master fields' is not needed as we
are now looping over fields in binary log, not over fields in
slave table.
- fill_extra_persistent_columns() is now using table->cond_set to know
which columns where not updated from binlog.
- Simplified get_table_data(TABLE *table_arg) by returning found
table_list.
- Errors for row events are now initialized in compatible_with(),
checked in check_wrong_column_usage() and reported in
give_compatibility_error().
Test cases and some code patchs provide by Brandon Nesterenko
<brandon.nesterenko@mariadb.com>
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| .. | ||
| archive | ||
| atomic | ||
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| binlog_encryption | ||
| client | ||
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| csv | ||
| encryption | ||
| engines | ||
| federated | ||
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| galera | ||
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| maria | ||
| mariabackup | ||
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