/*
 * contrib/pgstattuple/pgstattuple.c
 *
 * 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 "access/gist_private.h"
#include "access/hash.h"
#include "access/nbtree.h"
#include "access/relscan.h"
#include "catalog/namespace.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "utils/builtins.h"
#include "utils/tqual.h"


PG_MODULE_MAGIC;

PG_FUNCTION_INFO_V1(pgstattuple);
PG_FUNCTION_INFO_V1(pgstattuplebyid);

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

/*
 * struct pgstattuple_type
 *
 * tuple_percent, dead_tuple_percent and free_percent are computable,
 * so not defined here.
 */
typedef struct pgstattuple_type
{
	uint64		table_len;
	uint64		tuple_count;
	uint64		tuple_len;
	uint64		dead_tuple_count;
	uint64		dead_tuple_len;
	uint64		free_space;		/* free/reusable space in bytes */
} pgstattuple_type;

typedef void (*pgstat_page) (pgstattuple_type *, Relation, BlockNumber);

static Datum build_pgstattuple_type(pgstattuple_type *stat,
					   FunctionCallInfo fcinfo);
static Datum pgstat_relation(Relation rel, FunctionCallInfo fcinfo);
static Datum pgstat_heap(Relation rel, FunctionCallInfo fcinfo);
static void pgstat_btree_page(pgstattuple_type *stat,
				  Relation rel, BlockNumber blkno);
static void pgstat_hash_page(pgstattuple_type *stat,
				 Relation rel, BlockNumber blkno);
static void pgstat_gist_page(pgstattuple_type *stat,
				 Relation rel, BlockNumber blkno);
static Datum pgstat_index(Relation rel, BlockNumber start,
			 pgstat_page pagefn, FunctionCallInfo fcinfo);
static void pgstat_index_page(pgstattuple_type *stat, Page page,
				  OffsetNumber minoff, OffsetNumber maxoff);

/*
 * build_pgstattuple_type -- build a pgstattuple_type tuple
 */
static Datum
build_pgstattuple_type(pgstattuple_type *stat, FunctionCallInfo fcinfo)
{
#define NCOLUMNS	9
#define NCHARS		32

	HeapTuple	tuple;
	char	   *values[NCOLUMNS];
	char		values_buf[NCOLUMNS][NCHARS];
	int			i;
	double		tuple_percent;
	double		dead_tuple_percent;
	double		free_percent;	/* free/reusable space in % */
	TupleDesc	tupdesc;
	AttInMetadata *attinmeta;

	/* 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");

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

	if (stat->table_len == 0)
	{
		tuple_percent = 0.0;
		dead_tuple_percent = 0.0;
		free_percent = 0.0;
	}
	else
	{
		tuple_percent = 100.0 * stat->tuple_len / stat->table_len;
		dead_tuple_percent = 100.0 * stat->dead_tuple_len / stat->table_len;
		free_percent = 100.0 * stat->free_space / stat->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.
	 */
	for (i = 0; i < NCOLUMNS; i++)
		values[i] = values_buf[i];
	i = 0;
	snprintf(values[i++], NCHARS, INT64_FORMAT, stat->table_len);
	snprintf(values[i++], NCHARS, INT64_FORMAT, stat->tuple_count);
	snprintf(values[i++], NCHARS, INT64_FORMAT, stat->tuple_len);
	snprintf(values[i++], NCHARS, "%.2f", tuple_percent);
	snprintf(values[i++], NCHARS, INT64_FORMAT, stat->dead_tuple_count);
	snprintf(values[i++], NCHARS, INT64_FORMAT, stat->dead_tuple_len);
	snprintf(values[i++], NCHARS, "%.2f", dead_tuple_percent);
	snprintf(values[i++], NCHARS, INT64_FORMAT, stat->free_space);
	snprintf(values[i++], NCHARS, "%.2f", free_percent);

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

	/* make the tuple into a datum */
	return HeapTupleGetDatum(tuple);
}

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

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

	if (!superuser())
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 (errmsg("must be superuser to use pgstattuple functions"))));

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

	PG_RETURN_DATUM(pgstat_relation(rel, fcinfo));
}

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

	if (!superuser())
		ereport(ERROR,
				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
				 (errmsg("must be superuser to use pgstattuple functions"))));

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

	PG_RETURN_DATUM(pgstat_relation(rel, fcinfo));
}

/*
 * pgstat_relation
 */
static Datum
pgstat_relation(Relation rel, FunctionCallInfo fcinfo)
{
	const char *err;

	/*
	 * 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 (RELATION_IS_OTHER_TEMP(rel))
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("cannot access temporary tables of other sessions")));

	switch (rel->rd_rel->relkind)
	{
		case RELKIND_RELATION:
		case RELKIND_TOASTVALUE:
		case RELKIND_UNCATALOGED:
		case RELKIND_SEQUENCE:
			return pgstat_heap(rel, fcinfo);
		case RELKIND_INDEX:
			switch (rel->rd_rel->relam)
			{
				case BTREE_AM_OID:
					return pgstat_index(rel, BTREE_METAPAGE + 1,
										pgstat_btree_page, fcinfo);
				case HASH_AM_OID:
					return pgstat_index(rel, HASH_METAPAGE + 1,
										pgstat_hash_page, fcinfo);
				case GIST_AM_OID:
					return pgstat_index(rel, GIST_ROOT_BLKNO + 1,
										pgstat_gist_page, fcinfo);
				case GIN_AM_OID:
					err = "gin index";
					break;
				default:
					err = "unknown index";
					break;
			}
			break;
		case RELKIND_VIEW:
			err = "view";
			break;
		case RELKIND_COMPOSITE_TYPE:
			err = "composite type";
			break;
		default:
			err = "unknown";
			break;
	}

	ereport(ERROR,
			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
			 errmsg("\"%s\" (%s) is not supported",
					RelationGetRelationName(rel), err)));
	return 0;					/* should not happen */
}

/*
 * pgstat_heap -- returns live/dead tuples info in a heap
 */
static Datum
pgstat_heap(Relation rel, FunctionCallInfo fcinfo)
{
	HeapScanDesc scan;
	HeapTuple	tuple;
	BlockNumber nblocks;
	BlockNumber block = 0;		/* next block to count free space in */
	BlockNumber tupblock;
	Buffer		buffer;
	pgstattuple_type stat = {0};

	/* Disable syncscan because we assume we scan from block zero upwards */
	scan = heap_beginscan_strat(rel, SnapshotAny, 0, NULL, true, false);

	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 HeapTupleSatisfiesVisibility */
		LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

		if (HeapTupleSatisfiesVisibility(tuple, SnapshotNow, scan->rs_cbuf))
		{
			stat.tuple_len += tuple->t_len;
			stat.tuple_count++;
		}
		else
		{
			stat.dead_tuple_len += tuple->t_len;
			stat.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);
			stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
			UnlockReleaseBuffer(buffer);
			block++;
		}
	}
	heap_endscan(scan);

	while (block < nblocks)
	{
		CHECK_FOR_INTERRUPTS();

		buffer = ReadBuffer(rel, block);
		LockBuffer(buffer, BUFFER_LOCK_SHARE);
		stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
		UnlockReleaseBuffer(buffer);
		block++;
	}

	relation_close(rel, AccessShareLock);

	stat.table_len = (uint64) nblocks *BLCKSZ;

	return build_pgstattuple_type(&stat, fcinfo);
}

/*
 * pgstat_btree_page -- check tuples in a btree page
 */
static void
pgstat_btree_page(pgstattuple_type *stat, Relation rel, BlockNumber blkno)
{
	Buffer		buf;
	Page		page;

	buf = ReadBuffer(rel, blkno);
	LockBuffer(buf, BT_READ);
	page = BufferGetPage(buf);

	/* Page is valid, see what to do with it */
	if (PageIsNew(page))
	{
		/* fully empty page */
		stat->free_space += BLCKSZ;
	}
	else
	{
		BTPageOpaque opaque;

		opaque = (BTPageOpaque) PageGetSpecialPointer(page);
		if (opaque->btpo_flags & (BTP_DELETED | BTP_HALF_DEAD))
		{
			/* recyclable page */
			stat->free_space += BLCKSZ;
		}
		else if (P_ISLEAF(opaque))
		{
			pgstat_index_page(stat, page, P_FIRSTDATAKEY(opaque),
							  PageGetMaxOffsetNumber(page));
		}
		else
		{
			/* root or node */
		}
	}

	_bt_relbuf(rel, buf);
}

/*
 * pgstat_hash_page -- check tuples in a hash page
 */
static void
pgstat_hash_page(pgstattuple_type *stat, Relation rel, BlockNumber blkno)
{
	Buffer		buf;
	Page		page;

	_hash_getlock(rel, blkno, HASH_SHARE);
	buf = _hash_getbuf(rel, blkno, HASH_READ, 0);
	page = BufferGetPage(buf);

	if (PageGetSpecialSize(page) == MAXALIGN(sizeof(HashPageOpaqueData)))
	{
		HashPageOpaque opaque;

		opaque = (HashPageOpaque) PageGetSpecialPointer(page);
		switch (opaque->hasho_flag)
		{
			case LH_UNUSED_PAGE:
				stat->free_space += BLCKSZ;
				break;
			case LH_BUCKET_PAGE:
			case LH_OVERFLOW_PAGE:
				pgstat_index_page(stat, page, FirstOffsetNumber,
								  PageGetMaxOffsetNumber(page));
				break;
			case LH_BITMAP_PAGE:
			case LH_META_PAGE:
			default:
				break;
		}
	}
	else
	{
		/* maybe corrupted */
	}

	_hash_relbuf(rel, buf);
	_hash_droplock(rel, blkno, HASH_SHARE);
}

/*
 * pgstat_gist_page -- check tuples in a gist page
 */
static void
pgstat_gist_page(pgstattuple_type *stat, Relation rel, BlockNumber blkno)
{
	Buffer		buf;
	Page		page;

	buf = ReadBuffer(rel, blkno);
	LockBuffer(buf, GIST_SHARE);
	gistcheckpage(rel, buf);
	page = BufferGetPage(buf);

	if (GistPageIsLeaf(page))
	{
		pgstat_index_page(stat, page, FirstOffsetNumber,
						  PageGetMaxOffsetNumber(page));
	}
	else
	{
		/* root or node */
	}

	UnlockReleaseBuffer(buf);
}

/*
 * pgstat_index -- returns live/dead tuples info in a generic index
 */
static Datum
pgstat_index(Relation rel, BlockNumber start, pgstat_page pagefn,
			 FunctionCallInfo fcinfo)
{
	BlockNumber nblocks;
	BlockNumber blkno;
	pgstattuple_type stat = {0};

	blkno = start;
	for (;;)
	{
		/* Get the current relation length */
		LockRelationForExtension(rel, ExclusiveLock);
		nblocks = RelationGetNumberOfBlocks(rel);
		UnlockRelationForExtension(rel, ExclusiveLock);

		/* Quit if we've scanned the whole relation */
		if (blkno >= nblocks)
		{
			stat.table_len = (uint64) nblocks *BLCKSZ;

			break;
		}

		for (; blkno < nblocks; blkno++)
		{
			CHECK_FOR_INTERRUPTS();

			pagefn(&stat, rel, blkno);
		}
	}

	relation_close(rel, AccessShareLock);

	return build_pgstattuple_type(&stat, fcinfo);
}

/*
 * pgstat_index_page -- for generic index page
 */
static void
pgstat_index_page(pgstattuple_type *stat, Page page,
				  OffsetNumber minoff, OffsetNumber maxoff)
{
	OffsetNumber i;

	stat->free_space += PageGetFreeSpace(page);

	for (i = minoff; i <= maxoff; i = OffsetNumberNext(i))
	{
		ItemId		itemid = PageGetItemId(page, i);

		if (ItemIdIsDead(itemid))
		{
			stat->dead_tuple_count++;
			stat->dead_tuple_len += ItemIdGetLength(itemid);
		}
		else
		{
			stat->tuple_count++;
			stat->tuple_len += ItemIdGetLength(itemid);
		}
	}
}
