/*
 * $PostgreSQL: pgsql/contrib/pgstattuple/pgstattuple.c,v 1.20.2.2 2010/04/02 16:17:18 tgl Exp $
 *
 * Copyright (c) 2001,2002	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 "fmgr.h"
#include "funcapi.h"
#include "access/heapam.h"
#include "access/transam.h"
#include "catalog/namespace.h"
#include "miscadmin.h"
#include "utils/builtins.h"


PG_FUNCTION_INFO_V1(pgstattuple);
PG_FUNCTION_INFO_V1(pgstattuplebyid);

extern Datum pgstattuple(PG_FUNCTION_ARGS);
extern Datum pgstattuplebyid(PG_FUNCTION_ARGS);

static Datum pgstattuple_real(Relation rel, FunctionCallInfo fcinfo);


/* ----------
 * pgstattuple:
 * returns live/dead tuples info
 *
 * C FUNCTION definition
 * pgstattuple(text) returns pgstattuple_type
 * see pgstattuple.sql for pgstattuple_type
 * ----------
 */

#define NCOLUMNS 9
#define NCHARS 32

Datum
pgstattuple(PG_FUNCTION_ARGS)
{
	text	   *relname = PG_GETARG_TEXT_P(0);
	RangeVar   *relrv;
	Relation	rel;
	Datum		result;

	/* open relation */
	relrv = makeRangeVarFromNameList(textToQualifiedNameList(relname));
	rel = heap_openrv(relrv, AccessShareLock);

	result = pgstattuple_real(rel, fcinfo);

	PG_RETURN_DATUM(result);
}

Datum
pgstattuplebyid(PG_FUNCTION_ARGS)
{
	Oid			relid = PG_GETARG_OID(0);
	Relation	rel;
	Datum		result;

	/* open relation */
	rel = heap_open(relid, AccessShareLock);

	result = pgstattuple_real(rel, fcinfo);

	PG_RETURN_DATUM(result);
}

/*
 * pgstattuple_real
 *
 * The real work occurs here
 */
static Datum
pgstattuple_real(Relation rel, FunctionCallInfo fcinfo)
{
	HeapScanDesc scan;
	HeapTuple	tuple;
	BlockNumber nblocks;
	BlockNumber block = 0;		/* next block to count free space in */
	BlockNumber tupblock;
	Buffer		buffer;
	uint64		table_len;
	uint64		tuple_len = 0;
	uint64		dead_tuple_len = 0;
	uint64		tuple_count = 0;
	uint64		dead_tuple_count = 0;
	double		tuple_percent;
	double		dead_tuple_percent;
	uint64		free_space = 0; /* free/reusable space in bytes */
	double		free_percent;	/* free/reusable space in % */
	TupleDesc	tupdesc;
	AttInMetadata *attinmeta;
	char	  **values;
	int			i;
	Datum		result;

	/*
	 * Reject attempts to read non-local temporary relations; we would
	 * be likely to get wrong data since we have no visibility into the
	 * owning session's local buffers.
	 */
	if (isOtherTempNamespace(RelationGetNamespace(rel)))
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("cannot access temporary tables of other sessions")));

	/* 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");

	/* make sure we have a persistent copy of the tupdesc */
	tupdesc = CreateTupleDescCopy(tupdesc);

	/*
	 * Generate attribute metadata needed later to produce tuples from raw C
	 * strings
	 */
	attinmeta = TupleDescGetAttInMetadata(tupdesc);

	scan = heap_beginscan(rel, SnapshotAny, 0, NULL);

	nblocks = scan->rs_nblocks; /* # blocks to be scanned */

	/* scan the relation */
	while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
	{
		CHECK_FOR_INTERRUPTS();

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

		if (HeapTupleSatisfiesNow(tuple->t_data, scan->rs_cbuf))
		{
			tuple_len += tuple->t_len;
			tuple_count++;
		}
		else
		{
			dead_tuple_len += tuple->t_len;
			dead_tuple_count++;
		}

		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);

		/*
		 * To avoid physically reading the table twice, try to do the
		 * free-space scan in parallel with the heap scan.	However,
		 * heap_getnext may find no tuples on a given page, so we cannot
		 * simply examine the pages returned by the heap scan.
		 */
		tupblock = BlockIdGetBlockNumber(&tuple->t_self.ip_blkid);

		while (block <= tupblock)
		{
			CHECK_FOR_INTERRUPTS();

			buffer = ReadBuffer(rel, block);
			LockBuffer(buffer, BUFFER_LOCK_SHARE);
			free_space += PageGetFreeSpace((Page) BufferGetPage(buffer));
			LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
			ReleaseBuffer(buffer);
			block++;
		}
	}
	heap_endscan(scan);

	while (block < nblocks)
	{
		CHECK_FOR_INTERRUPTS();

		buffer = ReadBuffer(rel, block);
		free_space += PageGetFreeSpace((Page) BufferGetPage(buffer));
		ReleaseBuffer(buffer);
		block++;
	}

	heap_close(rel, AccessShareLock);

	table_len = (uint64) nblocks *BLCKSZ;

	if (nblocks == 0)
	{
		tuple_percent = 0.0;
		dead_tuple_percent = 0.0;
		free_percent = 0.0;
	}
	else
	{
		tuple_percent = (double) tuple_len *100.0 / table_len;
		dead_tuple_percent = (double) dead_tuple_len *100.0 / table_len;
		free_percent = (double) free_space *100.0 / table_len;
	}

	/*
	 * Prepare a values array for constructing the tuple. This should be an
	 * array of C strings which will be processed later by the appropriate
	 * "in" functions.
	 */
	values = (char **) palloc(NCOLUMNS * sizeof(char *));
	for (i = 0; i < NCOLUMNS; i++)
		values[i] = (char *) palloc(NCHARS * sizeof(char));
	i = 0;
	snprintf(values[i++], NCHARS, INT64_FORMAT, table_len);
	snprintf(values[i++], NCHARS, INT64_FORMAT, tuple_count);
	snprintf(values[i++], NCHARS, INT64_FORMAT, tuple_len);
	snprintf(values[i++], NCHARS, "%.2f", tuple_percent);
	snprintf(values[i++], NCHARS, INT64_FORMAT, dead_tuple_count);
	snprintf(values[i++], NCHARS, INT64_FORMAT, dead_tuple_len);
	snprintf(values[i++], NCHARS, "%.2f", dead_tuple_percent);
	snprintf(values[i++], NCHARS, INT64_FORMAT, free_space);
	snprintf(values[i++], NCHARS, "%.2f", free_percent);

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

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

	/* Clean up */
	for (i = 0; i < NCOLUMNS; i++)
		pfree(values[i]);
	pfree(values);

	return (result);
}
