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This variable indicates the number of least significant bits within the 32-bit server_id  which actually identify the server. Indicating that the server is actually identified by fewer than 32 bits makes it possible for some of the remaining bits to be used for other purposes, such as storing user data generated by applications using the NDB API’s Event API within the AnyValue  of an OperationOptions  structure (NDB Cluster uses the AnyValue  to store the server ID). 

When extracting the effective server ID from server_id  for purposes such as detection of replication loops, the server ignores the remaining bits. The server_id_bits  variable is used to mask out any irrelevant bits of server_id  in the I/O and SQL threads when deciding whether an event should be ignored based on the server ID. 

This data can be read from the binary log by mysqlbinlog , provided that it is run with its own server_id_bits  variable set to 32 (the default). 

If the value of server_id  greater than or equal to 2 to the power of server_id_bits ; otherwise, mysqld  refuses to start. 

This system variable is supported only by NDB Cluster. It is not supported in the standard MySQL 8.0 Server. 

• slave_allow_batching 

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Whether or not batched updates are enabled on NDB Cluster replicas. 

Setting this variable has an effect only when using replication with the NDB  storage engine; in MySQL Server 8.0, it is present but does nothing. For more information, see Section 23.6.6, “Starting NDB Cluster Replication (Single Replication Channel)” . 

• transaction_allow_batching 

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