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Implement sharable row-level locks, and use them for foreign key references

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to eliminate unnecessary deadlocks.  This commit adds SELECT ... FOR SHARE
paralleling SELECT ... FOR UPDATE.  The implementation uses a new SLRU
data structure (managed much like pg_subtrans) to represent multiple-
transaction-ID sets.  When more than one transaction is holding a shared
lock on a particular row, we create a MultiXactId representing that set
of transactions and store its ID in the row's XMAX.  This scheme allows
an effectively unlimited number of row locks, just as we did before,
while not costing any extra overhead except when a shared lock actually
has to be shared.   Still TODO: use the regular lock manager to control
the grant order when multiple backends are waiting for a row lock.

Alvaro Herrera and Tom Lane.
This commit is contained in:
Tom Lane
2005-04-28 21:47:18 +00:00
parent d902e7d63b
commit bedb78d386
55 changed files with 2802 additions and 439 deletions
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28
src/include/access/htup.h
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@@ -1,4 +1,4 @@
/*-------------------------------------------------------------------------
/*-------------------------------------------------------------------------
*
* htup.h
* POSTGRES heap tuple definitions.
@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/htup.h,v 1.73 2005/03/28 01:50:34 tgl Exp $
* $PostgreSQL: pgsql/src/include/access/htup.h,v 1.74 2005/04/28 21:47:17 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -93,11 +93,11 @@ typedef struct HeapTupleFields
{
TransactionId t_xmin; /* inserting xact ID */
CommandId t_cmin; /* inserting command ID */
TransactionId t_xmax; /* deleting xact ID */
TransactionId t_xmax; /* deleting or locking xact ID */
union
{
CommandId t_cmax; /* deleting command ID */
CommandId t_cmax; /* deleting or locking command ID */
TransactionId t_xvac; /* VACUUM FULL xact ID */
} t_field4;
} HeapTupleFields;
@@ -152,12 +152,16 @@ typedef HeapTupleHeaderData *HeapTupleHeader;
* attribute(s) */
#define HEAP_HASEXTENDED 0x000C /* the two above combined */
#define HEAP_HASOID 0x0010 /* has an object-id field */
/* 0x0020, 0x0040 and 0x0080 are unused */
/* 0x0020 is presently unused */
#define HEAP_XMAX_EXCL_LOCK 0x0040 /* xmax is exclusive locker */
#define HEAP_XMAX_SHARED_LOCK 0x0080 /* xmax is shared locker */
/* if either LOCK bit is set, xmax hasn't deleted the tuple, only locked it */
#define HEAP_IS_LOCKED (HEAP_XMAX_EXCL_LOCK | HEAP_XMAX_SHARED_LOCK)
#define HEAP_XMIN_COMMITTED 0x0100 /* t_xmin committed */
#define HEAP_XMIN_INVALID 0x0200 /* t_xmin invalid/aborted */
#define HEAP_XMAX_COMMITTED 0x0400 /* t_xmax committed */
#define HEAP_XMAX_INVALID 0x0800 /* t_xmax invalid/aborted */
#define HEAP_MARKED_FOR_UPDATE 0x1000 /* marked for UPDATE */
#define HEAP_XMAX_IS_MULTI 0x1000 /* t_xmax is a MultiXactId */
#define HEAP_UPDATED 0x2000 /* this is UPDATEd version of row */
#define HEAP_MOVED_OFF 0x4000 /* moved to another place by
* VACUUM FULL */
@@ -406,7 +410,8 @@ typedef HeapTupleData *HeapTuple;
#define XLOG_HEAP_MOVE 0x30
#define XLOG_HEAP_CLEAN 0x40
#define XLOG_HEAP_NEWPAGE 0x50
/* opcodes 0x60, 0x70 still free */
#define XLOG_HEAP_LOCK 0x60
/* opcode 0x70 still free */
#define XLOG_HEAP_OPMASK 0x70
/*
* When we insert 1st item on new page in INSERT/UPDATE
@@ -496,4 +501,13 @@ typedef struct xl_heap_newpage
#define SizeOfHeapNewpage (offsetof(xl_heap_newpage, blkno) + sizeof(BlockNumber))
/* This is what we need to know about lock */
typedef struct xl_heap_lock
{
xl_heaptid target; /* locked tuple id */
bool shared_lock; /* shared or exclusive row lock? */
} xl_heap_lock;
#define SizeOfHeapLock (offsetof(xl_heap_lock, shared_lock) + sizeof(bool))
#endif /* HTUP_H */