From f3e12c7567cd11fcf118adb14d9fc22f84a51b84 Mon Sep 17 00:00:00 2001
From: Konstantin Osipov <kostja@sun.com>
Date: Wed, 2 Jun 2010 12:06:07 +0400
Subject: [PATCH] Add comments to a few MDL deadlock-search related variables
and methods.
---
sql/mdl.cc | 12 +++++++++++-
sql/mdl.h | 1 +
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/sql/mdl.cc b/sql/mdl.cc
index ba938f8714b..b3702997168 100644
--- a/sql/mdl.cc
+++ b/sql/mdl.cc
@@ -119,8 +119,18 @@ class Deadlock_detection_context
victim(NULL),
current_search_depth(0)
{ }
+ /**
+ The context which has initiated the search. There
+ can be multiple searches happening in parallel at the same time.
+ */
MDL_context *start;
+ /** If a deadlock is found, the context that identifies the victim. */
MDL_context *victim;
+ /** Set to the MAX_SEARCH_DEPTH at start. Decreased whenever
+ we descend into another MDL context (aka traverse to the next
+ wait-for graph node). When 0 is reached, we assume that
+ a deadlock is found, even if we have not found a loop.
+ */
uint current_search_depth;
/**
Maximum depth for deadlock searches. After this depth is
@@ -408,7 +418,7 @@ mdl_locks_key(const uchar *record, size_t *length,
statement, the design capitalizes on that to later save on
look ups in the table definition cache. This leads to reduced
contention overall and on LOCK_open in particular.
- Please see the description of MDL_context::acquire_shared_lock()
+ Please see the description of MDL_context::acquire_lock_impl()
for details.
*/
diff --git a/sql/mdl.h b/sql/mdl.h
index 2e296b73057..1a123d5baa9 100644
--- a/sql/mdl.h
+++ b/sql/mdl.h
@@ -322,6 +322,7 @@ class MDL_request
DBUG_ASSERT(ticket == NULL);
type= type_arg;
}
+ /* A helper used to determine which lock request should be aborted. */
uint get_deadlock_weight() const;
static MDL_request *create(MDL_key::enum_mdl_namespace mdl_namespace,
--
2.30.9