xact.c

PostgreSQL7.4.6 for Linux

/*-------------------------------------------------------------------------
 *
 * xact.c
 *	  top level transaction system support routines
 *
 * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.156.2.1 2004/08/11 04:08:00 tgl Exp $
 *
 * NOTES
 *		Transaction aborts can now occur two ways:
 *
 *		1)	system dies from some internal cause  (syntax error, etc..)
 *		2)	user types ABORT
 *
 *		These two cases used to be treated identically, but now
 *		we need to distinguish them.  Why?	consider the following
 *		two situations:
 *
 *				case 1							case 2
 *				------							------
 *		1) user types BEGIN				1) user types BEGIN
 *		2) user does something			2) user does something
 *		3) user does not like what		3) system aborts for some reason
 *		   she sees and types ABORT
 *
 *		In case 1, we want to abort the transaction and return to the
 *		default state.	In case 2, there may be more commands coming
 *		our way which are part of the same transaction block and we have
 *		to ignore these commands until we see a COMMIT transaction or
 *		ROLLBACK.
 *
 *		Internal aborts are now handled by AbortTransactionBlock(), just as
 *		they always have been, and user aborts are now handled by
 *		UserAbortTransactionBlock().  Both of them rely on AbortTransaction()
 *		to do all the real work.  The only difference is what state we
 *		enter after AbortTransaction() does its work:
 *
 *		* AbortTransactionBlock() leaves us in TBLOCK_ABORT and
 *		* UserAbortTransactionBlock() leaves us in TBLOCK_ENDABORT
 *
 *		Low-level transaction abort handling is divided into two phases:
 *		* AbortTransaction() executes as soon as we realize the transaction
 *		  has failed.  It should release all shared resources (locks etc)
 *		  so that we do not delay other backends unnecessarily.
 *		* CleanupTransaction() executes when we finally see a user COMMIT
 *		  or ROLLBACK command; it cleans things up and gets us out of
 *		  the transaction internally.  In particular, we mustn't destroy
 *		  TopTransactionContext until this point.
 *
 *	 NOTES
 *		The essential aspects of the transaction system are:
 *
 *				o  transaction id generation
 *				o  transaction log updating
 *				o  memory cleanup
 *				o  cache invalidation
 *				o  lock cleanup
 *
 *		Hence, the functional division of the transaction code is
 *		based on which of the above things need to be done during
 *		a start/commit/abort transaction.  For instance, the
 *		routine AtCommit_Memory() takes care of all the memory
 *		cleanup stuff done at commit time.
 *
 *		The code is layered as follows:
 *
 *				StartTransaction
 *				CommitTransaction
 *				AbortTransaction
 *				CleanupTransaction
 *
 *		are provided to do the lower level work like recording
 *		the transaction status in the log and doing memory cleanup.
 *		above these routines are another set of functions:
 *
 *				StartTransactionCommand
 *				CommitTransactionCommand
 *				AbortCurrentTransaction
 *
 *		These are the routines used in the postgres main processing
 *		loop.  They are sensitive to the current transaction block state
 *		and make calls to the lower level routines appropriately.
 *
 *		Support for transaction blocks is provided via the functions:
 *
 *				StartTransactionBlock
 *				CommitTransactionBlock
 *				AbortTransactionBlock
 *
 *		These are invoked only in response to a user "BEGIN WORK", "COMMIT",
 *		or "ROLLBACK" command.	The tricky part about these functions
 *		is that they are called within the postgres main loop, in between
 *		the StartTransactionCommand() and CommitTransactionCommand().
 *
 *		For example, consider the following sequence of user commands:
 *
 *		1)		begin
 *		2)		select * from foo
 *		3)		insert into foo (bar = baz)
 *		4)		commit
 *
 *		in the main processing loop, this results in the following
 *		transaction sequence:
 *
 *			/	StartTransactionCommand();
 *		1) /	ProcessUtility();				<< begin
 *		   \		StartTransactionBlock();
 *			\	CommitTransactionCommand();
 *
 *			/	StartTransactionCommand();
 *		2) <	ProcessQuery();					<< select * from foo
 *			\	CommitTransactionCommand();
 *
 *			/	StartTransactionCommand();
 *		3) <	ProcessQuery();					<< insert into foo (bar = baz)
 *			\	CommitTransactionCommand();
 *
 *			/	StartTransactionCommand();
 *		4) /	ProcessUtility();				<< commit
 *		   \		CommitTransactionBlock();
 *			\	CommitTransactionCommand();
 *
 *		The point of this example is to demonstrate the need for
 *		StartTransactionCommand() and CommitTransactionCommand() to
 *		be state smart -- they should do nothing in between the calls
 *		to StartTransactionBlock() and EndTransactionBlock() and
 *		outside these calls they need to do normal start/commit
 *		processing.
 *
 *		Furthermore, suppose the "select * from foo" caused an abort
 *		condition.	We would then want to abort the transaction and
 *		ignore all subsequent commands up to the "commit".
 *		-cim 3/23/90
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <unistd.h>
#include <sys/time.h>

#include "access/gistscan.h"
#include "access/hash.h"
#include "access/nbtree.h"
#include "access/rtree.h"
#include "access/xact.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "catalog/namespace.h"
#include "commands/async.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "commands/user.h"
#include "executor/spi.h"
#include "libpq/be-fsstubs.h"
#include "miscadmin.h"
#include "storage/proc.h"
#include "storage/sinval.h"
#include "storage/smgr.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/portal.h"
#include "utils/catcache.h"
#include "utils/relcache.h"
#include "pgstat.h"


static void AbortTransaction(void);
static void AtAbort_Cache(void);
static void AtAbort_Locks(void);
static void AtAbort_Memory(void);
static void AtCleanup_Memory(void);
static void AtCommit_Cache(void);
static void AtCommit_LocalCache(void);
static void AtCommit_Locks(void);
static void AtCommit_Memory(void);
static void AtStart_Cache(void);
static void AtStart_Locks(void);
static void AtStart_Memory(void);
static void CallEOXactCallbacks(bool isCommit);
static void CleanupTransaction(void);
static void CommitTransaction(void);
static void RecordTransactionAbort(void);
static void StartTransaction(void);

/*
 *	global variables holding the current transaction state.
 */
static TransactionStateData CurrentTransactionStateData = {
	0,							/* transaction id */
	FirstCommandId,				/* command id */
	0,							/* scan command id */
	0x0,						/* start time */
	TRANS_DEFAULT,				/* transaction state */
	TBLOCK_DEFAULT				/* transaction block state from the client
								 * perspective */
};

static TransactionState CurrentTransactionState = &CurrentTransactionStateData;

/*
 *	User-tweakable parameters
 */
int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
int			XactIsoLevel;

bool		DefaultXactReadOnly = false;
bool		XactReadOnly;

int			CommitDelay = 0;	/* precommit delay in microseconds */
int			CommitSiblings = 5; /* number of concurrent xacts needed to
								 * sleep */


/*
 * List of add-on end-of-xact callbacks
 */
typedef struct EOXactCallbackItem
{
	struct EOXactCallbackItem *next;
	EOXactCallback callback;
	void	   *arg;
} EOXactCallbackItem;

static EOXactCallbackItem *EOXact_callbacks = NULL;

static void (*_RollbackFunc) (void *) = NULL;
static void *_RollbackData = NULL;


/* ----------------------------------------------------------------
 *	transaction state accessors
 * ----------------------------------------------------------------
 */

#ifdef NOT_USED

/* --------------------------------
 *	TransactionFlushEnabled()
 *	SetTransactionFlushEnabled()
 *
 *	These are used to test and set the "TransactionFlushState"
 *	variable.  If this variable is true (the default), then
 *	the system will flush all dirty buffers to disk at the end
 *	of each transaction.   If false then we are assuming the
 *	buffer pool resides in stable main memory, in which case we
 *	only do writes as necessary.
 * --------------------------------
 */
static int	TransactionFlushState = 1;

int
TransactionFlushEnabled(void)
{
	return TransactionFlushState;
}

void
SetTransactionFlushEnabled(bool state)
{
	TransactionFlushState = (state == true);
}
#endif


/*
 *	IsTransactionState
 *
 *	This returns true if we are currently running a query
 *	within an executing transaction.
 */
bool
IsTransactionState(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->state)
	{
		case TRANS_DEFAULT:
			return false;
		case TRANS_START:
			return true;
		case TRANS_INPROGRESS:
			return true;
		case TRANS_COMMIT:
			return true;
		case TRANS_ABORT:
			return true;
	}

	/*
	 * Shouldn't get here, but lint is not happy with this...
	 */
	return false;
}

/*
 *	IsAbortedTransactionBlockState
 *
 *	This returns true if we are currently running a query
 *	within an aborted transaction block.
 */
bool
IsAbortedTransactionBlockState(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->blockState == TBLOCK_ABORT)
		return true;

	return false;
}


/*
 *	GetCurrentTransactionId
 */
TransactionId
GetCurrentTransactionId(void)
{
	TransactionState s = CurrentTransactionState;

	return s->transactionIdData;
}


/*
 *	GetCurrentCommandId
 */
CommandId
GetCurrentCommandId(void)
{
	TransactionState s = CurrentTransactionState;

	return s->commandId;
}


/*
 *	GetCurrentTransactionStartTime
 */
AbsoluteTime
GetCurrentTransactionStartTime(void)
{
	TransactionState s = CurrentTransactionState;

	return s->startTime;
}


/*
 *	GetCurrentTransactionStartTimeUsec
 */
AbsoluteTime
GetCurrentTransactionStartTimeUsec(int *msec)
{
	TransactionState s = CurrentTransactionState;

	*msec = s->startTimeUsec;

	return s->startTime;
}


/*
 *	TransactionIdIsCurrentTransactionId
 *
 *	During bootstrap, we cheat and say "it's not my transaction ID" even though
 *	it is.	Along with transam.c's cheat to say that the bootstrap XID is
 *	already committed, this causes the tqual.c routines to see previously
 *	inserted tuples as committed, which is what we need during bootstrap.
 */
bool
TransactionIdIsCurrentTransactionId(TransactionId xid)
{
	TransactionState s = CurrentTransactionState;

	if (AMI_OVERRIDE)
	{
		Assert(xid == BootstrapTransactionId);
		return false;
	}

	return TransactionIdEquals(xid, s->transactionIdData);
}


/*
 *	CommandIdIsCurrentCommandId
 */
bool
CommandIdIsCurrentCommandId(CommandId cid)
{
	TransactionState s = CurrentTransactionState;

	return (cid == s->commandId) ? true : false;
}


/*
 *	CommandCounterIncrement
 */
void
CommandCounterIncrement(void)
{
	TransactionState s = CurrentTransactionState;

	s->commandId += 1;
	if (s->commandId == FirstCommandId) /* check for overflow */
		ereport(ERROR,
				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
				 errmsg("cannot have more than 2^32-1 commands in a transaction")));

	/* Propagate new command ID into query snapshots, if set */
	if (QuerySnapshot)
		QuerySnapshot->curcid = s->commandId;
	if (SerializableSnapshot)
		SerializableSnapshot->curcid = s->commandId;

	/*
	 * make cache changes visible to me.  AtCommit_LocalCache() instead of
	 * AtCommit_Cache() is called here.
	 */
	AtCommit_LocalCache();
	AtStart_Cache();
}


/* ----------------------------------------------------------------
 *						StartTransaction stuff
 * ----------------------------------------------------------------
 */

/*
 *	AtStart_Cache
 */
static void
AtStart_Cache(void)
{
	AcceptInvalidationMessages();
}

/*
 *		AtStart_Locks
 */
static void
AtStart_Locks(void)
{
	/*
	 * at present, it is unknown to me what belongs here -cim 3/18/90
	 *
	 * There isn't anything to do at the start of a xact for locks. -mer
	 * 5/24/92
	 */
}

/*
 *	AtStart_Memory
 */
static void
AtStart_Memory(void)
{
	/*