13.4.2.3 CHANGE REPLICATION SOURCE TO Statement

Makes the replication channel assign a GTID to replicated transactions that do not have one, enabling replication from a source that does not use GTID-based replication, to a replica that does. For a multi-source replica, you can have a mix of channels that use ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS, and channels that do not. The default is OFF, meaning that the feature is not used.

LOCAL assigns a GTID including the replica's own UUID (the server_uuid setting). uuid assigns a GTID including the specified UUID, such as the server_uuid setting for the replication source server. Using a nonlocal UUID lets you differentiate between transactions that originated on the replica and transactions that originated on the source, and for a multi-source replica, between transactions that originated on different sources. The UUID you choose only has significance for the replica's own use. If any of the transactions sent by the source do have a GTID already, that GTID is retained.

Channels specific to Group Replication cannot use ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS, but an asynchronous replication channel for another source on a server instance that is a Group Replication group member can do so. In that case, do not specify the Group Replication group name as the UUID for creating the GTIDs.

To set ASSIGN_GTIDS_TO_ANONYMOUS_TRANSACTIONS to LOCAL or uuid, the replica must have gtid_mode=ON set, and this cannot be changed afterwards. This option is for use with a source that has binary log file position based replication, so MASTER_AUTO_POSITION=1 cannot be set for the channel. Both the replication SQL thread and the replication I/O (receiver) thread must be stopped before setting this option.

For further restrictions and information, see Section 17.1.3.6, “Replication From a Source Without GTIDs to a Replica With GTIDs”.

Enables RSA key pair-based password exchange by requesting the public key from the source. The option is disabled by default.

This option applies to replicas that authenticate with the caching_sha2_password authentication plugin. For connections by accounts that authenticate using this plugin, the source does not send the public key unless requested, so it must be requested or specified in the client. If SOURCE_PUBLIC_KEY_PATH is given and specifies a valid public key file, it takes precedence over GET_SOURCE_PUBLIC_KEY. If you are using a replication user account that authenticates with the caching_sha2_password plugin (which is the default from MySQL 8.0), and you are not using a secure connection, you must specify either this option or the SOURCE_PUBLIC_KEY_PATH option to provide the RSA public key to the replica.

Stops the replication channel persisting file names and file positions in the replication metadata repositories. GTID_ONLY is available as of MySQL 8.0.27. The GTID_ONLY option is disabled by default for asynchronous replication channels, but it is enabled by default for Group Replication channels, and it cannot be disabled for them.

For replication channels with this setting, in-memory file positions are still tracked, and file positions can still be observed for debugging purposes in error messages and through interfaces such as SHOW REPLICA STATUS statements (where they are shown as being invalid if they are out of date). However, the writes and reads required to persist and check the file positions are avoided in situations where GTID-based replication does not actually require them, including the transaction queuing and application process.

This option can be used only if both the replication SQL (applier) thread and replication I/O (receiver) thread are stopped. To set GTID_ONLY = 1 for a replication channel, GTIDs must be in use on the server (gtid_mode = ON), and row-based binary logging must be in use on the source (statement-based replication is not supported). The options REQUIRE_ROW_FORMAT = 1 and SOURCE_AUTO_POSITION = 1 must be set for the replication channel.

When GTID_ONLY = 1 is set, the replica uses replica_parallel_workers=1 if that system variable is set to zero for the server, so it is always technically a multi-threaded applier. This is because a multi-threaded applier uses saved positions rather than the replication metadata repositories to locate the start of a transaction that it needs to reapply.

If you disable GTID_ONLY after setting it, the existing relay logs are deleted and the existing known binary log file positions are persisted, even if they are stale. The file positions for the binary log and relay log in the replication metadata repositories might be invalid, and a warning is returned if this is the case. Provided that SOURCE_AUTO_POSITION is still enabled, GTID auto-positioning is used to provide the correct positioning.

If you also disable SOURCE_AUTO_POSITION, the file positions for the binary log and relay log in the replication metadata repositories are used for positioning if they are valid. If they are marked as invalid, you must provide a valid binary log file name and position (SOURCE_LOG_FILE and SOURCE_LOG_POS). If you also provide a relay log file name and position (RELAY_LOG_FILE and RELAY_LOG_POS), the relay logs are preserved and the applier position is set to the stated position. GTID auto-skip ensures that any transactions already applied are skipped even if the eventual applier position is not correct.

Makes the replica ignore events originating from the specified servers. The option takes a comma-separated list of 0 or more server IDs. Log rotation and deletion events from the servers are not ignored, and are recorded in the relay log.

In circular replication, the originating server normally acts as the terminator of its own events, so that they are not applied more than once. Thus, this option is useful in circular replication when one of the servers in the circle is removed. Suppose that you have a circular replication setup with 4 servers, having server IDs 1, 2, 3, and 4, and server 3 fails. When bridging the gap by starting replication from server 2 to server 4, you can include IGNORE_SERVER_IDS = (3) in the CHANGE REPLICATION SOURCE TO statement that you issue on server 4 to tell it to use server 2 as its source instead of server 3. Doing so causes it to ignore and not to propagate any statements that originated with the server that is no longer in use.

If IGNORE_SERVER_IDS contains the server's own ID and the server was started with the --replicate-same-server-id option enabled, an error results.

The source metadata repository and the output of SHOW REPLICA STATUS provide the list of servers that are currently ignored. For more information, see Section 17.2.4.2, “Replication Metadata Repositories”, and Section 13.7.7.35, “SHOW REPLICA STATUS Statement”.

If a CHANGE REPLICATION SOURCE TO statement is issued without any IGNORE_SERVER_IDS option, any existing list is preserved. To clear the list of ignored servers, it is necessary to use the option with an empty list:

CHANGE REPLICATION SOURCE TO IGNORE_SERVER_IDS = ();

RESET REPLICA ALL clears IGNORE_SERVER_IDS.

The network namespace to use for TCP/IP connections to the replication source server or, if the MySQL communication stack is in use, for Group Replication’s group communication connections. The maximum length of the string value is 64 characters. If this option is omitted, connections from the replica use the default (global) namespace. On platforms that do not implement network namespace support, failure occurs when the replica attempts to connect to the source. For information about network namespaces, see Section 5.1.14, “Network Namespace Support”. NETWORK_NAMESPACE is available as of MySQL 8.0.22.

Names a user account that supplies a security context for the specified channel. NULL, which is the default, means no security context is used. PRIVILEGE_CHECKS_USER is available as of MySQL 8.0.18.

The user name and host name for the user account must follow the syntax described in Section 6.2.4, “Specifying Account Names”, and the user must not be an anonymous user (with a blank user name) or the CURRENT_USER. The account must have the REPLICATION_APPLIER privilege, plus the required privileges to execute the transactions replicated on the channel. For details of the privileges required by the account, see Section 17.3.3, “Replication Privilege Checks”. When you restart the replication channel, the privilege checks are applied from that point on. If you do not specify a channel and no other channels exist, the statement is applied to the default channel.

The use of row-based binary logging is strongly recommended when PRIVILEGE_CHECKS_USER is set, and you can set REQUIRE_ROW_FORMAT to enforce this. For example, to start privilege checks on the channel channel_1 on a running replica, issue the following statements:

STOP REPLICA FOR CHANNEL 'channel_1';
 
CHANGE REPLICATION SOURCE TO
    PRIVILEGE_CHECKS_USER = 'user'@'host',
    REQUIRE_ROW_FORMAT = 1,
    FOR CHANNEL 'channel_1';
 
START REPLICA FOR CHANNEL 'channel_1';

The relay log file name, and the location in that file, at which the replication SQL thread begins reading from the replica's relay log the next time the thread starts. RELAY_LOG_FILE can use either an absolute or relative path, and uses the same base name as SOURCE_LOG_FILE. The maximum length of the string value is 511 characters.

A CHANGE REPLICATION SOURCE TO statement using RELAY_LOG_FILE, RELAY_LOG_POS, or both options can be executed on a running replica when the replication SQL (applier) thread is stopped. Relay logs are preserved if at least one of the replication applier thread and the replication I/O (receiver) thread is running. If both threads are stopped, all relay log files are deleted unless at least one of RELAY_LOG_FILE or RELAY_LOG_POS is specified. For the Group Replication applier channel (group_replication_applier), which only has an applier thread and no receiver thread, this is the case if the applier thread is stopped, but with that channel you cannot use the RELAY_LOG_FILE and RELAY_LOG_POS options.

Permits only row-based replication events to be processed by the replication channel. This option prevents the replication applier from taking actions such as creating temporary tables and executing LOAD DATA INFILE requests, which increases the security of the channel. The REQUIRE_ROW_FORMAT option is disabled by default for asynchronous replication channels, but it is enabled by default for Group Replication channels, and it cannot be disabled for them. For more information, see Section 17.3.3, “Replication Privilege Checks”. REQUIRE_ROW_FORMAT is available as of MySQL 8.0.19.

Enables a replica to select its own policy for primary key checks. The default is STREAM. REQUIRE_TABLE_PRIMARY_KEY_CHECK is available as of MySQL 8.0.20.

When the option is set to ON for a replication channel, the replica always uses the value ON for the sql_require_primary_key system variable in replication operations, requiring a primary key. When the option is set to OFF, the replica always uses the value OFF for sql_require_primary_key in replication operations, so that a primary key is never required, even if the source required one. When the REQUIRE_TABLE_PRIMARY_KEY_CHECK option is set to STREAM, which is the default, the replica uses whatever value is replicated from the source for each transaction.

For multisource replication, setting REQUIRE_TABLE_PRIMARY_KEY_CHECK to ON or OFF enables a replica to normalize behavior across the replication channels for different sources, and keep a consistent setting for the sql_require_primary_key system variable. Using ON safeguards against the accidental loss of primary keys when multiple sources update the same set of tables. Using OFF allows sources that can manipulate primary keys to work alongside sources that cannot.

When PRIVILEGE_CHECKS_USER is set, setting REQUIRE_TABLE_PRIMARY_KEY_CHECK to ON or OFF means that the user account does not need session administration level privileges to set restricted session variables, which are required to change the value of sql_require_primary_key to match the source's setting for each transaction. For more information, see Section 17.3.3, “Replication Privilege Checks”.

Makes the replica attempt to connect to the source using the auto-positioning feature of GTID-based replication, rather than a binary log file based position. This option is used to start a replica using GTID-based replication. The default is 0, meaning that GTID auto-positioning and GTID-based replication are not used. This option can be used with CHANGE REPLICATION SOURCE TO only if both the replication SQL (applier) thread and replication I/O (receiver) thread are stopped.

Both the replica and the source must have GTIDs enabled (GTID_MODE=ON, ON_PERMISSIVE, or OFF_PERMISSIVE on the replica, and GTID_MODE=ON on the source). SOURCE_LOG_FILE, SOURCE_LOG_POS, RELAY_LOG_FILE, and RELAY_LOG_POS cannot be specified together with SOURCE_AUTO_POSITION = 1. If multi-source replication is enabled on the replica, you need to set the SOURCE_AUTO_POSITION = 1 option for each applicable replication channel.

With SOURCE_AUTO_POSITION = 1 set, in the initial connection handshake, the replica sends a GTID set containing the transactions that it has already received, committed, or both. The source responds by sending all transactions recorded in its binary log whose GTID is not included in the GTID set sent by the replica. This exchange ensures that the source only sends the transactions with a GTID that the replica has not already recorded or committed. If the replica receives transactions from more than one source, as in the case of a diamond topology, the auto-skip function ensures that the transactions are not applied twice. For details of how the GTID set sent by the replica is computed, see Section 17.1.3.3, “GTID Auto-Positioning”.

If any of the transactions that should be sent by the source have been purged from the source's binary log, or added to the set of GTIDs in the gtid_purged system variable by another method, the source sends the error ER_MASTER_HAS_PURGED_REQUIRED_GTIDS to the replica, and replication does not start. The GTIDs of the missing purged transactions are identified and listed in the source's error log in the warning message ER_FOUND_MISSING_GTIDS. Also, if during the exchange of transactions it is found that the replica has recorded or committed transactions with the source's UUID in the GTID, but the source itself has not committed them, the source sends the error ER_SLAVE_HAS_MORE_GTIDS_THAN_MASTER to the replica and replication does not start. For information on how to handle these situations, see Section 17.1.3.3, “GTID Auto-Positioning”.

You can see whether replication is running with GTID auto-positioning enabled by checking the Performance Schema replication_connection_status table or the output of SHOW REPLICA STATUS. Disabling the SOURCE_AUTO_POSITION option again makes the replica revert to file-based replication.

Determines which of the replica's network interfaces is chosen for connecting to the source, for use on replicas that have multiple network interfaces. Specify the IP address of the network interface. The maximum length of the string value is 255 characters.

The IP address configured with this option, if any, can be seen in the Source_Bind column of the output from SHOW REPLICA STATUS. In the source metadata repository table mysql.slave_master_info, the value can be seen as the Source_bind column. The ability to bind a replica to a specific network interface is also supported by NDB Cluster.

Specifies one, two, or three of the permitted compression algorithms for connections to the replication source server, separated by commas. The maximum length of the string value is 99 characters. The default value is uncompressed.

The available algorithms are zlib, zstd, and uncompressed, the same as for the protocol_compression_algorithms system variable. The algorithms can be specified in any order, but it is not an order of preference - the algorithm negotiation process attempts to use zlib, then zstd, then uncompressed, if they are specified. SOURCE_COMPRESSION_ALGORITHMS is available as of MySQL 8.0.18.

The value of SOURCE_COMPRESSION_ALGORITHMS applies only if the replica_compressed_protocol or slave_compressed_protocol system variable is disabled. If replica_compressed_protocol or slave_compressed_protocol is enabled, it takes precedence over SOURCE_COMPRESSION_ALGORITHMS and connections to the source use zlib compression if both source and replica support that algorithm. For more information, see Section 4.2.8, “Connection Compression Control”.

Binary log transaction compression (available as of MySQL 8.0.20), which is activated by the binlog_transaction_compression system variable, can also be used to save bandwidth. If you do this in combination with connection compression, connection compression has less opportunity to act on the data, but can still compress headers and those events and transaction payloads that are uncompressed. For more information on binary log transaction compression, see Section 5.4.4.5, “Binary Log Transaction Compression”.

Specifies the interval in seconds between the reconnection attempts that the replica makes after the connection to the source times out. The default interval is 60.

The number of attempts is limited by the SOURCE_RETRY_COUNT option. If both the default settings are used, the replica waits 60 seconds between reconnection attempts (SOURCE_CONNECT_RETRY=60), and keeps attempting to reconnect at this rate for 60 days (SOURCE_RETRY_COUNT=86400). These values are recorded in the source metadata repository and shown in the replication_connection_configuration Performance Schema table.

Activates the asynchronous connection failover mechanism for a replication channel if one or more alternative replication source servers are available (so when there are multiple MySQL servers or groups of servers that share the replicated data). SOURCE_CONNECTION_AUTO_FAILOVER is available as of MySQL 8.0.22. The default is 0, meaning that the mechanism is not activated. For full information and instructions to set up this feature, see Section 17.4.9.2, “Asynchronous Connection Failover for Replicas”.

The asynchronous connection failover mechanism takes over after the reconnection attempts controlled by SOURCE_CONNECT_RETRY and SOURCE_RETRY_COUNT are exhausted. It reconnects the replica to an alternative source chosen from a specified source list, which you manage using the asynchronous_connection_failover_add_source and asynchronous_connection_failover_delete_source functions. To add and remove managed groups of servers, use the asynchronous_connection_failover_add_managed and asynchronous_connection_failover_delete_managed functions instead. For more information, see Section 17.4.9, “Switching Sources and Replicas with Asynchronous Connection Failover”.

Specifies how many seconds behind the source the replica must lag. An event received from the source is not executed until at least interval seconds later than its execution on the source. interval must be a nonnegative integer in the range from 0 to 2³¹−1. The default is 0. For more information, see Section 17.4.11, “Delayed Replication”.

A CHANGE REPLICATION SOURCE TO statement using the SOURCE_DELAY option can be executed on a running replica when the replication SQL thread is stopped.

Controls the heartbeat interval, which stops the connection timeout occurring in the absence of data if the connection is still good. A heartbeat signal is sent to the replica after that number of seconds, and the waiting period is reset whenever the source's binary log is updated with an event. Heartbeats are therefore sent by the source only if there are no unsent events in the binary log file for a period longer than this.

The heartbeat interval interval is a decimal value having the range 0 to 4294967 seconds and a resolution in milliseconds; the smallest nonzero value is 0.001. Setting interval to 0 disables heartbeats altogether. The heartbeat interval defaults to half the value of the replica_net_timeout or slave_net_timeout system variable. It is recorded in the source metadata repository and shown in the replication_connection_configuration Performance Schema table. Issuing RESET REPLICA resets the heartbeat interval to the default value.

The system variable replica_net_timeout (from MySQL 8.0.26) or slave_net_timeout (before MySQL 8.0.26) specifies the number of seconds that the replica waits for either more data or a heartbeat signal from the source, before the replica considers the connection broken, aborts the read, and tries to reconnect. The default value is 60 seconds (one minute). Note that a change to the value or default setting of replica_net_timeout or slave_net_timeout does not automatically change the heartbeat interval, whether that has been set explicitly or is using a previously calculated default. A warning is issued if you set the global value of replica_net_timeout or slave_net_timeout to a value less than that of the current heartbeat interval. If replica_net_timeout or slave_net_timeout is changed, you must also issue CHANGE REPLICATION SOURCE TO to adjust the heartbeat interval to an appropriate value so that the heartbeat signal occurs before the connection timeout. If you do not do this, the heartbeat signal has no effect, and if no data is received from the source, the replica can make repeated reconnection attempts, creating zombie dump threads.

The host name or IP address of the replication source server. The replica uses this to connect to the source. The maximum length of the string value is 255 characters.

If you specify SOURCE_HOST or SOURCE_PORT, the replica assumes that the source server is different from before (even if the option value is the same as its current value.) In this case, the old values for the source's binary log file name and position are considered no longer applicable, so if you do not specify SOURCE_LOG_FILE and SOURCE_LOG_POS in the statement, SOURCE_LOG_FILE='' and SOURCE_LOG_POS=4 are silently appended to it.

Setting SOURCE_HOST='' (that is, setting its value explicitly to an empty string) is not the same as not setting SOURCE_HOST at all. Trying to set SOURCE_HOST to an empty string fails with an error.

The binary log file name, and the location in that file, at which the replication I/O (receiver) thread begins reading from the source's binary log the next time the thread starts. Specify these options if you are using binary log file position based replication.

SOURCE_LOG_FILE must include the numeric suffix of a specific binary log file that is available on the source server, for example, SOURCE_LOG_FILE='binlog.000145'. The maximum length of the string value is 511 characters.

SOURCE_LOG_POS is the numeric position for the replica to start reading in that file. SOURCE_LOG_POS=4 represents the start of the events in a binary log file.

If you specify either of SOURCE_LOG_FILE or SOURCE_LOG_POS, you cannot specify SOURCE_AUTO_POSITION = 1, which is for GTID-based replication.

If neither of SOURCE_LOG_FILE or SOURCE_LOG_POS is specified, the replica uses the last coordinates of the replication SQL thread before CHANGE REPLICATION SOURCE TO was issued. This ensures that there is no discontinuity in replication, even if the replication SQL (applier) thread was late compared to the replication I/O (receiver) thread.

The password for the replication user account to use for connecting to the replication source server. The maximum length of the string value is 32 characters. If you specify SOURCE_PASSWORD, SOURCE_USER is also required.

The password used for a replication user account in a CHANGE REPLICATION SOURCE TO statement is limited to 32 characters in length. Trying to use a password of more than 32 characters causes CHANGE REPLICATION SOURCE TO to fail.

The password is masked in MySQL Server’s logs, Performance Schema tables, and SHOW PROCESSLIST statements.

The TCP/IP port number that the replica uses to connect to the replication source server.

If you specify SOURCE_HOST or SOURCE_PORT, the replica assumes that the source server is different from before (even if the option value is the same as its current value.) In this case, the old values for the source's binary log file name and position are considered no longer applicable, so if you do not specify SOURCE_LOG_FILE and SOURCE_LOG_POS in the statement, SOURCE_LOG_FILE='' and SOURCE_LOG_POS=4 are silently appended to it.

Enables RSA key pair-based password exchange by providing the path name to a file containing a replica-side copy of the public key required by the source. The file must be in PEM format. The maximum length of the string value is 511 characters.

This option applies to replicas that authenticate with the sha256_password or caching_sha2_password authentication plugin. (For sha256_password, SOURCE_PUBLIC_KEY_PATH can be used only if MySQL was built using OpenSSL.) If you are using a replication user account that authenticates with the caching_sha2_password plugin (which is the default from MySQL 8.0), and you are not using a secure connection, you must specify either this option or the GET_SOURCE_PUBLIC_KEY=1 option to provide the RSA public key to the replica.

Sets the maximum number of reconnection attempts that the replica makes after the connection to the source times out, as determined by the replica_net_timeout or slave_net_timeout system variable. If the replica does need to reconnect, the first retry occurs immediately after the timeout. The default is 86400 attempts.

The interval between the attempts is specified by the SOURCE_CONNECT_RETRY option. If both the default settings are used, the replica waits 60 seconds between reconnection attempts (SOURCE_CONNECT_RETRY=60), and keeps attempting to reconnect at this rate for 60 days (SOURCE_RETRY_COUNT=86400). A setting of 0 for SOURCE_RETRY_COUNT means that there is no limit on the number of reconnection attempts, so the replica keeps trying to reconnect indefinitely.

The values for SOURCE_CONNECT_RETRY and SOURCE_RETRY_COUNT are recorded in the source metadata repository and shown in the replication_connection_configuration Performance Schema table. SOURCE_RETRY_COUNT supersedes the --master-retry-count server startup option.

Specify whether the replica encrypts the replication connection. The default is 0, meaning that the replica does not encrypt the replication connection. If you set SOURCE_SSL=1, you can configure the encryption using the SOURCE_SSL_xxx and SOURCE_TLS_xxx options.

Setting SOURCE_SSL=1 for a replication connection and then setting no further SOURCE_SSL_xxx options corresponds to setting --ssl-mode=REQUIRED for the client, as described in Command Options for Encrypted Connections. With SOURCE_SSL=1, the connection attempt only succeeds if an encrypted connection can be established. A replication connection does not fall back to an unencrypted connection, so there is no setting corresponding to the --ssl-mode=PREFERRED setting for replication. If SOURCE_SSL=0 is set, this corresponds to --ssl-mode=DISABLED.

Specify how the replica uses encryption and ciphers to secure the replication connection. These options can be changed even on replicas that are compiled without SSL support. They are saved to the source metadata repository, but are ignored if the replica does not have SSL support enabled. The maximum length of the value for the string-valued SOURCE_SSL_xxx and SOURCE_TLS_xxx options is 511 characters, with the exception of SOURCE_TLS_CIPHERSUITES, for which it is 4000 characters.

The SOURCE_SSL_xxx and SOURCE_TLS_xxx options perform the same functions as the --ssl-xxx and --tls-xxx client options described in Command Options for Encrypted Connections. The correspondence between the two sets of options, and the use of the SOURCE_SSL_xxx and SOURCE_TLS_xxx options to set up a secure connection, is explained in Section 17.3.1, “Setting Up Replication to Use Encrypted Connections”.

The user name for the replication user account to use for connecting to the replication source server. The maximum length of the string value is 96 characters.

For Group Replication, this account must exist on every member of the replication group. It is used for distributed recovery if the XCom communication stack is in use for the group, and also used for group communication connections if the MySQL communication stack is in use for the group. With the MySQL communication stack, the account must have the GROUP_REPLICATION_STREAM permission.

It is possible to set an empty user name by specifying SOURCE_USER='', but the replication channel cannot be started with an empty user name. In releases before MySQL 8.0.21, only set an empty SOURCE_USER user name if you need to clear previously used credentials from the replication metadata repositories for security purposes. Do not use the channel afterwards, due to a bug in these releases that can substitute a default user name if an empty user name is read from the repositories (for example, during an automatic restart of a Group Replication channel). From MySQL 8.0.21, it is valid to set an empty SOURCE_USER user name and use the channel afterwards if you always provide user credentials using the START REPLICA statement or START GROUP_REPLICATION statement that starts the replication channel. This approach means that the replication channel always needs operator intervention to restart, but the user credentials are not recorded in the replication metadata repositories.

The compression level to use for connections to the replication source server that use the zstd compression algorithm. SOURCE_ZSTD_COMPRESSION_LEVEL is available as of MySQL 8.0.18. The permitted levels are from 1 to 22, with larger values indicating increasing levels of compression. The default level is 3.

The compression level setting has no effect on connections that do not use zstd compression. For more information, see Section 4.2.8, “Connection Compression Control”.