From MySQL 8.0.20, you can enable binary log transaction
compression on a MySQL server instance. When binary log
transaction compression is enabled, transaction payloads are
compressed using the zstd algorithm, and then written to the
server's binary log file as a single event (a
transaction payloads remain in a compressed state while they are
sent in the replication stream to replicas, other Group
Replication group members, or clients such as
mysqlbinlog. They are not decompressed by
receiver threads, and are written to the relay log still in
their compressed state. Binary log transaction compression
therefore saves storage space both on the originator of the
transaction and on the recipient (and for their backups), and
saves network bandwidth when the transactions are sent between
Compressed transaction payloads are decompressed when the
individual events contained in them need to be inspected. For
decompressed by an applier thread in order to apply the events
it contains on the recipient. Decompression is also carried out
during recovery, by mysqlbinlog when
replaying transactions, and by the
BINLOG EVENTS and
You can enable binary log transaction compression on a MySQL
server instance using the
system variable, which defaults to
can also use the
system variable to set the level for the zstd algorithm that is
used for compression. This value determines the compression
effort, from 1 (the lowest effort) to 22 (the highest effort).
As the compression level increases, the compression ratio
increases, which reduces the storage space and network bandwidth
required for the transaction payload. However, the effort
required for data compression also increases, taking time and
CPU and memory resources on the originating server. Increases in
the compression effort do not have a linear relationship to
increases in the compression ratio.
The following types of event are excluded from binary log transaction compression, so are always written uncompressed to the binary log:
Events relating to the GTID for the transaction (including anonymous GTID events).
Other types of control event, such as view change events and heartbeat events.
Incident events and the whole of any transactions that contain them. For example, a transaction during which the server stopped would not have its payload compressed.
Non-transactional events and the whole of any transactions that contain them. For example, a transaction involving a mix of non-transactional and transactional storage engines would not have its payload compressed.
Events that are logged using statement-based binary logging. Binary log transaction compression is only applied for the row-based binary logging format.
Binary log encryption can be used on binary log files that contain compressed transactions.
Transactions with payloads that are compressed can be rolled back like any other transaction, and they can also be filtered out on a replica by the usual filtering options. Binary log transaction compression can be applied to XA transactions.
When binary log transaction compression is enabled, the
limits for the server still apply, and are measured on the
compressed size of the
Transaction_payload_event, plus the bytes
used for the event header. Note that compressed transaction
payloads are sent as a single packet, rather than each event
of the transaction being sent in an individual packet, as is
the case when binary log transaction compression is not in
For multithreaded workers, each transaction (including its
GTID event and
is assigned to a worker thread. The worker thread decompresses
the transaction payload and applies the individual events in
it one by one. If an error is found applying any event within
Transaction_payload_event, the complete
transaction is reported to the co-ordinator as having failed.
DATABASE, all the databases affected
by the transaction are mapped before the transaction is
scheduled. The use of binary log transaction compression with
DATABASE policy can reduce parallelism
compared to uncompressed transactions, which are mapped and
scheduled for each event.
For semisynchronous replication (see
Section 17.4.9, “Semisynchronous Replication”), the replica
acknowledges the transaction when the complete
Transaction_payload_event has been
When binary log checksums are enabled (which is the default),
the replication source server does not write checksums for
individual events in a compressed transaction payload.
Instead, a checksum is written for the complete
Transaction_payload_event, and indivdual
checksums are written for any events that were not compressed,
such as events relating to GTIDs.
For operations that reference the end position of an event,
START SLAVE with the
must specify the end position of the compressed transaction
When skipping events using
compressed transaction payload is counted as a single counter
value, so all the events inside it are skipped as a unit.
MySQL Server releases that support binary log transaction compression can handle a mix of compressed and uncompressed transaction payloads.
The system variables relating to binary log transaction compression do not need to be set the same on all Group Replication group members, and are not replicated from sources to replicas in a replication topology. You can decide whether or not binary log transaction compression is appropriate for each MySQL Server instance that has a binary log.
If transaction compression is enabled then disabled on a server, compression is not applied to future transactions originated on that server, but transaction payloads that have been compressed can still be handled and displayed.
If transaction compression is specified for individual sessions by setting the session value of
binlog_transaction_compression, the binary log can contain a mix of compressed and uncompressed transaction payloads.
When a source in a replication topology and its replica both have binary log transaction compression enabled, the replica receives compressed transaction payloads and writes them compressed to its relay log. It decompresses the transaction payloads to apply the transactions, and then compresses them again after applying for writing to its binary log. Any downstream replicas receive the compressed transaction payloads.
When a source in a replication topology has binary log transaction compression enabled but its replica does not, the replica receives compressed transaction payloads and writes them compressed to its relay log. It decompresses the transaction payloads to apply the transactions, and then writes them uncompressed to its own binary log, if it has one. Any downstream replicas receive the uncompressed transaction payloads.
When a source in a replication topology does not have binary log transaction compression enabled but its replica does, if the replica has a binary log, it compresses the transaction payloads after applying them, and writes the compressed transaction payloads to its binary log. Any downstream replicas receive the compressed transaction payloads.
When a MySQL server instance has no binary log, if it is at a
release from MySQL 8.0.20, it can receive, handle, and display
compressed transaction payloads regardless of its value for
Compressed transaction payloads received by such server
instances are written in their compressed state to the relay
log, so they benefit indirectly from compression that was
carried out by other servers in the replication topology.
A replica at a release before MySQL 8.0.20 cannot replicate from a source with binary log transaction compression enabled. A replica at or above MySQL 8.0.20 can replicate from a source at an earlier release that does not support binary log transaction compression, and can carry out its own compression on transactions received from that source when writing them to its own binary log.
You can monitor the effects of binary log transaction
compression using the Performance Schema table
The statistics include the data compression ratio for the
monitored period, and you can also view the effect of
compression on the last transaction on the server. You can
reset the statistics by truncating the table. Statistics for
binary logs and relay logs are split out so you can see the
impact of compression for each log type. The MySQL server
instance must have a binary log to produce these statistics.
The Performance Schema table
events_stages_current shows when
a transaction is in the stage of decompression or compression
for its transaction payload, and displays its progress for
this stage. Compression is carried out by the worker thread
handling the transaction, just before the transaction is
committed, provided that there are no events in the finalized
capture cache that exclude the transaction from binary log
transaction compression (for example, incident events). When
decompression is required, it is carried out for one event
from the payload at a time.
You can enable connection compression at the protocol level
for replication connections, using the
MASTER_ZSTD_COMPRESSION_LEVEL options of
CHANGE MASTER TO statement
(or the deprecated
system variable). If you enable binary log transaction
compression in a system where connection compression is also
enabled, the impact of connection compression is reduced, as
there might be little opportunity to further compress the
compressed transaction payloads. However, connection
compression can still operate on uncompressed events and on
message headers. Binary log transaction compression can be
worth enabling in combination with connection compression if
you need to save storage space as well as network bandwidth.
For more information on connection compression for replication
Section 4.2.8, “Connection Compression Control”.
For Group Replication, compression is enabled by default for
messages that exceed the threshold set by the
system variable. You can also configure compression for
messages sent for distributed recovery by the method of state
transfer from a donor's binary log, using the
system variables. If you enable binary log transaction
compression in a system where these are configured, Group
Replication's message compression can still operate on
uncompressed events and on message headers, but its impact is
reduced. For more information on message compression for Group
Section 18.6.3, “Message Compression”.