关于 MySQL Replication with Global Transaction Identifiers 的疑问

[JasonLaw]

在MySQL :: MySQL 8.0 Reference Manual :: 17.1.3.1 GTID Format and Storage中，有这么一段：

GTID assignment distinguishes between client transactions, which are committed on the source, and replicated transactions, which are reproduced on a replica. When a client transaction is committed on the source, it is assigned a new GTID, provided that the transaction was written to the binary log. Client transactions are guaranteed to have monotonically increasing GTIDs without gaps between the generated numbers. If a client transaction is not written to the binary log (for example, because the transaction was filtered out, or the transaction was read-only), it is not assigned a GTID on the server of origin.

它说“If a client transaction is not written to the binary log (for example, because the transaction was filtered out, or the transaction was read-only), it is not assigned a GTID on the server of origin.”，究竟是什么情况下，client transaction 会被 filtered out 呢？