DML statements executed on the primary node in a ColumnStore
cluster do not need to be written to the primary's binlog. This
is due to ColumnStore's distributed storage architecture.
With this patch, we disable writing to binlog when a DML statement
(INSERT/DELETE/UPDATE/LDI/INSERT..SELECT) is performed on a ColumnStore
table. HANDLER::external_lock() calls are used to
1. Turn OFF the OPTION_BIN_LOG flag
2. Turn ON the OPTION_BIN_TMP_LOG_OFF flag
in THD::variables.option_bits during a WRITE lock call.
THD::variables.option_bits is restored back to the original state
during the UNLOCK call in HANDLER::external_lock().
Further, isDMLStatement() function is added to reduce code verbosity
to check if a given statement is a DML statement.
Note that with this patch, not writing to primary's binlog means
DML replication from a ColumnStore cluster to another ColumnStore
cluster or to another foreign engine will not work.
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