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Cosmetic improvements to group locking.

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Reflow text in lock manager README so that it fits within 80 columns.
Correct some mistakes.  Expand the README to explain not only why group
locking exists but also the data structures that support it.  Improve
comments related to group locking several files.  Change the name of a
macro argument for improved clarity.

Most of these problems were reported by Tom Lane, but I found a few
of them myself.

Robert Haas and Tom Lane
This commit is contained in:
Robert Haas
2016-02-21 15:42:02 +05:30
parent dd077ef832
commit d91a4a6c85
5 changed files with 102 additions and 53 deletions
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21
src/backend/storage/lmgr/deadlock.c
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@@ -33,12 +33,21 @@
#include "utils/memutils.h"
/* One edge in the waits-for graph */
/*
* One edge in the waits-for graph.
*
* waiter and blocker may or may not be members of a lock group, but if either
* is, it will be the leader rather than any other member of the lock group.
* The group leaders act as representatives of the whole group even though
* those particular processes need not be waiting at all. There will be at
* least one member of the waiter's lock group on the wait queue for the given
* lock, maybe more.
*/
typedef struct
{
PGPROC *waiter; /* the waiting process */
PGPROC *blocker; /* the process it is waiting for */
LOCK *lock; /* the lock it is waiting for */
PGPROC *waiter; /* the leader of the waiting lock group */
PGPROC *blocker; /* the leader of the group it is waiting for */
LOCK *lock; /* the lock being waited for */
int pred; /* workspace for TopoSort */
int link; /* workspace for TopoSort */
} EDGE;
@@ -1006,8 +1015,8 @@ TopoSort(LOCK *lock,
return false;
/*
* Output everything in the lock group. There's no point in outputing
* an ordering where members of the same lock group are not
* Output everything in the lock group. There's no point in
* outputting an ordering where members of the same lock group are not
* consecutive on the wait queue: if some other waiter is between two
* requests that belong to the same group, then either it conflicts
* with both of them and is certainly not a solution; or it conflicts