MDEV-34857: After-review fixes.

Reviewed-by: Monty <monty@mariadb.org>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

mysql-test/main/mysqld--help.result

@@ -1305,7 +1305,7 @@ The following specify which files/extra groups are read (specified before remain
  Maximum time a slave DDL will wait for a blocking SELECT
  or other user query until that query will be aborted. The
  argument will be treated as a decimal value with
- microsecond precision
+ nanosecond precision
  --slave-compressed-protocol 
  Use compression on master/slave protocol
  --slave-connections-needed-for-purge=# 

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -4015,7 +4015,7 @@ COMMAND_LINE_ARGUMENT	OPTIONAL
 VARIABLE_NAME	SLAVE_ABORT_BLOCKING_TIMEOUT
 VARIABLE_SCOPE	GLOBAL
 VARIABLE_TYPE	DOUBLE
-VARIABLE_COMMENT	Maximum time a slave DDL will wait for a blocking SELECT or other user query until that query will be aborted. The argument will be treated as a decimal value with microsecond precision
+VARIABLE_COMMENT	Maximum time a slave DDL will wait for a blocking SELECT or other user query until that query will be aborted. The argument will be treated as a decimal value with nanosecond precision
 NUMERIC_MIN_VALUE	0
 NUMERIC_MAX_VALUE	31536000
 NUMERIC_BLOCK_SIZE	NULL

sql/mdl.cc

@@ -2404,6 +2404,11 @@ MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
   if (abort_blocking_timeout < lock_wait_timeout &&
       m_owner->get_thd()->rgi_slave)
   {
+    /*
+      After @@slave_abort_blocking_timeout seconds, kill non-replication
+      queries that are blocking a replication event (such as an ALTER TABLE)
+      from proceeding.
+    */
     set_timespec_nsec(abs_abort_blocking_timeout,
                       (ulonglong)(abort_blocking_timeout * 1000000000ULL));
     abort_blocking_enabled= true;
@@ -2428,7 +2433,7 @@ MDL_context::acquire_lock(MDL_request *mdl_request, double lock_wait_timeout)
       abort_blocking= true;
       abort_blocking_enabled= false;
     }
-    if (cmp_timespec(abs_shortwait, abs_timeout) > 0)
+    else if (cmp_timespec(abs_shortwait, abs_timeout) > 0)
       break;
 
     /* abs_timeout is far away. Wait a short while and notify locks. */

sql/sys_vars.cc

@@ -2598,7 +2598,7 @@ static Sys_var_on_access_global<
         "slave_abort_blocking_timeout",
         "Maximum time a slave DDL will wait for a blocking SELECT or other "
         "user query until that query will be aborted. The argument will be "
-        "treated as a decimal value with microsecond precision",
+        "treated as a decimal value with nanosecond precision",
         GLOBAL_VAR(slave_abort_blocking_timeout), CMD_LINE(REQUIRED_ARG),
         VALID_RANGE(0, LONG_TIMEOUT), DEFAULT(LONG_TIMEOUT), NO_MUTEX_GUARD,
         NOT_IN_BINLOG);