MDEV-4991: GTID binlog indexing

Improve the performance of slave connect using B+-Tree indexes on each binlog
file. The index allows fast lookup of a GTID position to the corresponding
offset in the binlog file, as well as lookup of a position to find the
corresponding GTID position.

This eliminates a costly sequential scan of the starting binlog file
to find the GTID starting position when a slave connects. This is
especially costly if the binlog file is not cached in memory (IO
cost), or if it is encrypted or a lot of slaves connect simultaneously
(CPU cost).

The size of the index files is generally less than 1% of the binlog data, so
not expected to be an issue.

Most of the work writing the index is done as a background task, in
the binlog background thread. This minimises the performance impact on
transaction commit. A simple global mutex is used to protect index
reads and (background) index writes; this is fine as slave connect is
a relatively infrequent operation.

Here are the user-visible options and status variables. The feature is on by
default and is expected to need no tuning or configuration for most users.

binlog_gtid_index
  On by default. Can be used to disable the indexes for testing purposes.

binlog_gtid_index_page_size (default 4096)
  Page size to use for the binlog GTID index. This is the size of the nodes
  in the B+-tree used internally in the index. A very small page-size (64 is
  the minimum) will be less efficient, but can be used to stress the
  BTree-code during testing.

binlog_gtid_index_span_min (default 65536)
  Control sparseness of the binlog GTID index. If set to N, at most one
  index record will be added for every N bytes of binlog file written.
  This can be used to reduce the number of records in the index, at
  the cost only of having to scan a few more events in the binlog file
  before finding the target position

Two status variables are available to monitor the use of the GTID indexes:

  Binlog_gtid_index_hit
  Binlog_gtid_index_miss

The "hit" status increments for each successful lookup in a GTID index.
The "miss" increments when a lookup is not possible. This indicates that the
index file is missing (eg. binlog written by old server version
without GTID index support), or corrupt.

Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

mysql-test/suite/perfschema/r/dml_setup_instruments.result

@@ -8,12 +8,12 @@ wait/synch/mutex/sql/Ack_receiver::mutex	YES	YES
 wait/synch/mutex/sql/Cversion_lock	YES	YES
 wait/synch/mutex/sql/Delayed_insert::mutex	YES	YES
 wait/synch/mutex/sql/Event_scheduler::LOCK_scheduler_state	YES	YES
+wait/synch/mutex/sql/Gtid_index_writer::gtid_index_mutex	YES	YES
 wait/synch/mutex/sql/gtid_waiting::LOCK_gtid_waiting	YES	YES
 wait/synch/mutex/sql/hash_filo::lock	YES	YES
 wait/synch/mutex/sql/HA_DATA_PARTITION::LOCK_auto_inc	YES	YES
 wait/synch/mutex/sql/LOCK_active_mi	YES	YES
 wait/synch/mutex/sql/LOCK_after_binlog_sync	YES	YES
-wait/synch/mutex/sql/LOCK_audit_mask	YES	YES
 select * from performance_schema.setup_instruments
 where name like 'Wait/Synch/Rwlock/sql/%'
   and name not in (

mysql-test/suite/perfschema/r/relaylog.result

@@ -23,6 +23,7 @@ from performance_schema.file_summary_by_instance
 where file_name like "%master-%" order by file_name;
 FILE_NAME	EVENT_NAME	COUNT_READ	COUNT_WRITE	SUM_NUMBER_OF_BYTES_READ	SUM_NUMBER_OF_BYTES_WRITE
 master-bin.000001	wait/io/file/sql/binlog	MANY	MANY	MANY	MANY
+master-bin.000001.idx	wait/io/file/sql/gtid_index	NONE	MANY	NONE	MANY
 master-bin.index	wait/io/file/sql/binlog_index	MANY	MANY	MANY	MANY
 select * from performance_schema.file_summary_by_instance
 where file_name like "%slave-%" order by file_name;
@@ -112,6 +113,7 @@ where file_name like "%slave-%"
 order by file_name;
 FILE_NAME	EVENT_NAME	COUNT_READ	COUNT_WRITE	SUM_NUMBER_OF_BYTES_READ	SUM_NUMBER_OF_BYTES_WRITE
 slave-bin.000001	wait/io/file/sql/binlog	MANY	MANY	MANY	MANY
+slave-bin.000001.idx	wait/io/file/sql/gtid_index	NONE	MANY	NONE	MANY
 slave-bin.index	wait/io/file/sql/binlog_index	MANY	MANY	MANY	MANY
 slave-relay-bin.000001	wait/io/file/sql/relaylog	MANY	MANY	MANY	MANY
 slave-relay-bin.000002	wait/io/file/sql/relaylog	MANY	MANY	MANY	MANY