postgresql/contrib/pgrowlocks/pgrowlocks.c

/*
 * contrib/pgrowlocks/pgrowlocks.c
 *
 * Copyright (c) 2005-2006	Tatsuo Ishii
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose, without fee, and without a
 * written agreement is hereby granted, provided that the above
 * copyright notice and this paragraph and the following two
 * paragraphs appear in all copies.
 *
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
 * LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
 * DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * THE AUTHOR SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS
 * IS" BASIS, AND THE AUTHOR HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
 * SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

#include "postgres.h"

#include "access/multixact.h"
#include "access/relscan.h"
#include "access/xact.h"
#include "catalog/namespace.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/procarray.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/rel.h"
#include "utils/tqual.h"


PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(pgrowlocks);

extern Datum pgrowlocks(PG_FUNCTION_ARGS);

/* ----------
 * pgrowlocks:
 * returns tids of rows being locked
 * ----------
 */

#define NCHARS 32

typedef struct
{
	Relation	rel;
	HeapScanDesc scan;
	int			ncolumns;
} MyData;

#define		Atnum_tid		0
#define		Atnum_xmax		1
#define		Atnum_ismulti	2
#define		Atnum_xids		3
#define		Atnum_modes		4
#define		Atnum_pids		5

Datum
pgrowlocks(PG_FUNCTION_ARGS)
{
	FuncCallContext *funcctx;
	HeapScanDesc scan;
	HeapTuple	tuple;
	TupleDesc	tupdesc;
	AttInMetadata *attinmeta;
	Datum		result;
	MyData	   *mydata;
	Relation	rel;

	if (SRF_IS_FIRSTCALL())
	{
		text	   *relname;
		RangeVar   *relrv;
		MemoryContext oldcontext;
		AclResult	aclresult;

		funcctx = SRF_FIRSTCALL_INIT();
		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

		/* Build a tuple descriptor for our result type */
		if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
			elog(ERROR, "return type must be a row type");

		attinmeta = TupleDescGetAttInMetadata(tupdesc);
		funcctx->attinmeta = attinmeta;

		relname = PG_GETARG_TEXT_P(0);
		relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
		rel = heap_openrv(relrv, AccessShareLock);

		/* check permissions: must have SELECT on table */
		aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
									  ACL_SELECT);
		if (aclresult != ACLCHECK_OK)
			aclcheck_error(aclresult, ACL_KIND_CLASS,
						   RelationGetRelationName(rel));

		scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
		mydata = palloc(sizeof(*mydata));
		mydata->rel = rel;
		mydata->scan = scan;
		mydata->ncolumns = tupdesc->natts;
		funcctx->user_fctx = mydata;

		MemoryContextSwitchTo(oldcontext);
	}

	funcctx = SRF_PERCALL_SETUP();
	attinmeta = funcctx->attinmeta;
	mydata = (MyData *) funcctx->user_fctx;
	scan = mydata->scan;

	/* scan the relation */
	while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
	{
		HTSU_Result	htsu;
		TransactionId xmax;
		uint16		infomask;

		/* must hold a buffer lock to call HeapTupleSatisfiesUpdate */
		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

		htsu = HeapTupleSatisfiesUpdate(tuple->t_data,
										GetCurrentCommandId(false),
										scan->rs_cbuf);
		xmax = HeapTupleHeaderGetRawXmax(tuple->t_data);
		infomask = tuple->t_data->t_infomask;

		/*
		 * a tuple is locked if HTSU returns BeingUpdated, and if it returns
		 * MayBeUpdated but the Xmax is valid and pointing at us.
		 */
		if (htsu == HeapTupleBeingUpdated ||
			(htsu == HeapTupleMayBeUpdated &&
			 !(infomask & HEAP_XMAX_INVALID) &&
			 !(infomask & HEAP_XMAX_IS_MULTI) &&
			 (xmax == GetCurrentTransactionIdIfAny())))
		{
			char	  **values;

			values = (char **) palloc(mydata->ncolumns * sizeof(char *));

			values[Atnum_tid] = (char *) DirectFunctionCall1(tidout,
															 PointerGetDatum(&tuple->t_self));

			values[Atnum_xmax] = palloc(NCHARS * sizeof(char));
			snprintf(values[Atnum_xmax], NCHARS, "%d", xmax);
			if (infomask & HEAP_XMAX_IS_MULTI)
			{
				MultiXactMember *members;
				int			nmembers;
				bool		first = true;
				bool		allow_old;

				values[Atnum_ismulti] = pstrdup("true");

				allow_old = !(infomask & HEAP_LOCK_MASK) &&
							 (infomask & HEAP_XMAX_LOCK_ONLY);
				nmembers = GetMultiXactIdMembers(xmax, &members, allow_old);
				if (nmembers == -1)
				{
					values[Atnum_xids] = "{0}";
					values[Atnum_modes] = "{transient upgrade status}";
					values[Atnum_pids] = "{0}";
				}
				else
				{
					int			j;

					values[Atnum_xids] = palloc(NCHARS * nmembers);
					values[Atnum_modes] = palloc(NCHARS * nmembers);
					values[Atnum_pids] = palloc(NCHARS * nmembers);

					strcpy(values[Atnum_xids], "{");
					strcpy(values[Atnum_modes], "{");
					strcpy(values[Atnum_pids], "{");

					for (j = 0; j < nmembers; j++)
					{
						char		buf[NCHARS];

						if (!first)
						{
							strcat(values[Atnum_xids], ",");
							strcat(values[Atnum_modes], ",");
							strcat(values[Atnum_pids], ",");
						}
						snprintf(buf, NCHARS, "%d", members[j].xid);
						strcat(values[Atnum_xids], buf);
						switch (members[j].status)
						{
							case MultiXactStatusUpdate:
								snprintf(buf, NCHARS, "Update");
								break;
							case MultiXactStatusNoKeyUpdate:
								snprintf(buf, NCHARS, "No Key Update");
								break;
							case MultiXactStatusForUpdate:
								snprintf(buf, NCHARS, "For Update");
								break;
							case MultiXactStatusForNoKeyUpdate:
								snprintf(buf, NCHARS, "For No Key Update");
								break;
							case MultiXactStatusForShare:
								snprintf(buf, NCHARS, "Share");
								break;
							case MultiXactStatusForKeyShare:
								snprintf(buf, NCHARS, "Key Share");
								break;
						}
						strcat(values[Atnum_modes], buf);
						snprintf(buf, NCHARS, "%d",
								 BackendXidGetPid(members[j].xid));
						strcat(values[Atnum_pids], buf);

						first = false;
					}

					strcat(values[Atnum_xids], "}");
					strcat(values[Atnum_modes], "}");
					strcat(values[Atnum_pids], "}");
				}
			}
			else
			{
				values[Atnum_ismulti] = pstrdup("false");

				values[Atnum_xids] = palloc(NCHARS * sizeof(char));
				snprintf(values[Atnum_xids], NCHARS, "{%d}", xmax);

				values[Atnum_modes] = palloc(NCHARS);
				if (infomask & HEAP_XMAX_LOCK_ONLY)
				{
					if (HEAP_XMAX_IS_SHR_LOCKED(infomask))
						snprintf(values[Atnum_modes], NCHARS, "{For Share}");
					else if (HEAP_XMAX_IS_KEYSHR_LOCKED(infomask))
						snprintf(values[Atnum_modes], NCHARS, "{For Key Share}");
					else if (HEAP_XMAX_IS_EXCL_LOCKED(infomask))
						snprintf(values[Atnum_modes], NCHARS, "{For Update}");
					else
						/* neither keyshare nor exclusive bit it set */
						snprintf(values[Atnum_modes], NCHARS,
								 "{transient upgrade status}");
				}
				else
				{
					if (tuple->t_data->t_infomask2 & HEAP_KEYS_UPDATED)
						snprintf(values[Atnum_modes], NCHARS, "{Key Update}");
					else
						snprintf(values[Atnum_modes], NCHARS, "{Update}");
				}

				values[Atnum_pids] = palloc(NCHARS * sizeof(char));
				snprintf(values[Atnum_pids], NCHARS, "{%d}",
						 BackendXidGetPid(xmax));
			}

			LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);

			/* build a tuple */
			tuple = BuildTupleFromCStrings(attinmeta, values);

			/* make the tuple into a datum */
			result = HeapTupleGetDatum(tuple);

			/*
			 * no need to pfree what we allocated; it's on a short-lived memory
			 * context anyway
			 */

			SRF_RETURN_NEXT(funcctx, result);
		}
		else
		{
			LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
		}
	}

	heap_endscan(scan);
	heap_close(mydata->rel, AccessShareLock);

	SRF_RETURN_DONE(funcctx);
}