Problem:
========
The mysqlbinlog tool is leaking memory, causing failures in various tests when
compiling and testing with AddressSanitizer or LeakSanitizer like this:
cmake -DCMAKE_BUILD_TYPE=Debug -DWITH_ASAN:BOOL=ON /path/to/source
make -j$(nproc)
cd mysql-test
ASAN_OPTIONS=abort_on_error=1 ./mtr --parallel=auto
Analysis:
=========
Two types of leaks were observed during above execution.
1) Leak in Log_event::read_log_event(char const*, unsigned int, char const**,
Format_description_log_event const*, char)
File: sql/log_event.cc:2150
For all row based replication events the memory which is allocated during
read_log_event is not freed after the event is processed. The event specific
memory has to be retained only when flashback option is enabled with
mysqlbinlog tool. In this case all the events are retained till the end
statement is received and they are processed in reverse order and they are
destroyed. But in the existing code all events are retained irrespective of
flashback mode. Hence the memory leaks are observed.
2) read_remote_annotate_event(unsigned char*, unsigned long, char const**)
File: client/mysqlbinlog.cc:194
In general the Annotate event is not printed immediately because all
subsequent rbr-events can be filtered away. Instead it will be printed
together with the first not filtered away Table map or the last rbr will be
processed. While reading remote annotate events memory is allocated for event
buffer and event's temp_buf is made to point to the allocated buffer as shown
below. The TRUE flag is used for doing proper cleanup using free_temp_buf().
i.e at the time of deletion of annotate event its destructor takes care of
clearing the temp_buf.
/*
Ensure the event->temp_buf is pointing to the allocated buffer.
(TRUE = free temp_buf on the event deletion)
*/
event->register_temp_buf((char*)event_buf, TRUE);
But existing code does the following when it receives a remote annotate_event.
if (remote_opt)
ev->temp_buf= 0;
That is code immediately sets temp_buf=0, because of which free_temp_buf()
call will return empty handed as it has lost the reference to the allocated
temporary buffer. This results in memory leak
Fix:
====
1) If not in flashback mode, destroy the memory for events once they are
processed.
2) Remove the ev->temp_buf=0 code for remote option. Let the proper cleanup to
be done as part of free_temp_buf().
Problem
-------
For one-statement contains multiple row events, Flashback didn't reverse the
sequence of row events inside one-statement.
Solution
--------
Using a new array 'events_in_stmt' to store the row events of one-statement,
when parsed the last one event, then print from the last one to the first one.
In the same time, fixed another bug, without -vv will not insert the table_map
into print_event_info->m_table_map, then change_to_flashback_event() will not
execute because of Table_map_log_event is empty.
When WSREP(thd) is not true we will use my_error(...) to print error. This
will set thd->is_error() to true and we wont be getting generic error.
Signed-off-by: Sachin Setiya <sachin.setiya@mariadb.com>
==== Description ====
Flashback can rollback the instances/databases/tables to an old snapshot.
It's implement on Server-Level by full image format binary logs (--binlog-row-image=FULL), so it supports all engines.
Currently, it’s a feature inside mysqlbinlog tool (with --flashback arguments).
Because the flashback binlog events will store in the memory, you should check if there is enough memory in your machine.
==== New Arguments to mysqlbinlog ====
--flashback (-B)
It will let mysqlbinlog to work on FLASHBACK mode.
==== New Arguments to mysqld ====
--flashback
Setup the server to use flashback. This enables binary log in row mode
and will enable extra logging for DDL's needed by flashback feature
==== Example ====
I have a table "t" in database "test", we can compare the output with "--flashback" and without.
#client/mysqlbinlog /data/mysqldata_10.0/binlog/mysql-bin.000001 -vv -d test -T t --start-datetime="2013-03-27 14:54:00" > /tmp/1.sql
#client/mysqlbinlog /data/mysqldata_10.0/binlog/mysql-bin.000001 -vv -d test -T t --start-datetime="2013-03-27 14:54:00" -B > /tmp/2.sql
Then, importing the output flashback file (/tmp/2.log), it can flashback your database/table to the special time (--start-datetime).
And if you know the exact postion, "--start-postion" is also works, mysqlbinlog will output the flashback logs that can flashback to "--start-postion" position.
==== Implement ====
1. As we know, if binlog_format is ROW (binlog-row-image=FULL in 10.1 and later), all columns value are store in the row event, so we can get the data before mis-operation.
2. Just do following things:
2.1 Change Event Type, INSERT->DELETE, DELETE->INSERT.
For example:
INSERT INTO t VALUES (...) ---> DELETE FROM t WHERE ...
DELETE FROM t ... ---> INSERT INTO t VALUES (...)
2.2 For Update_Event, swapping the SET part and WHERE part.
For example:
UPDATE t SET cols1 = vals1 WHERE cols2 = vals2
--->
UPDATE t SET cols2 = vals2 WHERE cols1 = vals1
2.3 For Multi-Rows Event, reverse the rows sequence, from the last row to the first row.
For example:
DELETE FROM t WHERE id=1; DELETE FROM t WHERE id=2; ...; DELETE FROM t WHERE id=n;
--->
DELETE FROM t WHERE id=n; ...; DELETE FROM t WHERE id=2; DELETE FROM t WHERE id=1;
2.4 Output those events from the last one to the first one which mis-operation happened.
For example:
