MDEV-6676: Optimistic parallel replication

Implement a new mode for parallel replication. In this mode, all transactions
are optimistically attempted applied in parallel. In case of conflicts, the
offending transaction is rolled back and retried later non-parallel.

This is an early-release patch to facilitate testing, more changes to user
interface / options will be expected. The new mode is not enabled by default.

1 files changed, 23 insertions, 1 deletions

diff --git a/sql/rpl_parallel.h b/sql/rpl_parallel.h
index 239818855b8..2062c89e62e 100644
--- a/sql/rpl_parallel.h
+++ b/sql/rpl_parallel.h
@@ -49,7 +49,29 @@ struct group_commit_orderer {
   uint64 wait_count;
   group_commit_orderer *prev_gco;
   group_commit_orderer *next_gco;
-  bool installed;
+  /*
+    This flag is set when this GCO has been installed into the next_gco pointer
+    of the previous GCO.
+  */
+  static const uint8 INSTALLED = 0x01;
+  /*
+    This flag is set for a GCO in which we have event groups with multiple
+    different commit_id values from the master. This happens when we
+    optimistically try to execute in parallel transactions not known to be
+    conflict-free.
+
+    When this flag is set, in case of DDL we need to start a new GCO regardless
+    of current commit_id, as DDL is not safe to speculatively apply in parallel
+    with prior event groups.
+  */
+  static const uint8 MULTI_BATCH = 0x02;
+  /*
+    This flag is set for a GCO that contains DDL. If set, it forces a switch to
+    a new GCO upon seeing a new commit_id, as DDL is not safe to speculatively
+    replicate in parallel with subsequent transactions.
+  */
+  static const uint8 FORCE_SWITCH = 0x04;
+  uint8 flags;
 };