tuptoaster.c

来自「PostgreSQL7.4.6 for Linux」· C语言 代码 · 共 1,307 行 · 第 1/3 页

/*-------------------------------------------------------------------------
 *
 * tuptoaster.c
 *	  Support routines for external and compressed storage of
 *	  variable size attributes.
 *
 * Copyright (c) 2000-2003, PostgreSQL Global Development Group
 *
 *
 * IDENTIFICATION
 *	  $Header: /cvsroot/pgsql/src/backend/access/heap/tuptoaster.c,v 1.38 2003/08/04 23:59:37 tgl Exp $
 *
 *
 * INTERFACE ROUTINES
 *		heap_tuple_toast_attrs -
 *			Try to make a given tuple fit into one page by compressing
 *			or moving off attributes
 *
 *		heap_tuple_untoast_attr -
 *			Fetch back a given value from the "secondary" relation
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <unistd.h>
#include <fcntl.h>

#include "access/heapam.h"
#include "access/genam.h"
#include "access/tuptoaster.h"
#include "catalog/catalog.h"
#include "utils/rel.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/pg_lzcompress.h"


#undef TOAST_DEBUG

static void toast_delete(Relation rel, HeapTuple oldtup);
static void toast_delete_datum(Relation rel, Datum value);
static void toast_insert_or_update(Relation rel, HeapTuple newtup,
					   HeapTuple oldtup);
static Datum toast_save_datum(Relation rel, Datum value);
static varattrib *toast_fetch_datum(varattrib *attr);
static varattrib *toast_fetch_datum_slice(varattrib *attr,
						int32 sliceoffset, int32 length);


/* ----------
 * heap_tuple_toast_attrs -
 *
 *	This is the central public entry point for toasting from heapam.
 *
 *	Calls the appropriate event specific action.
 * ----------
 */
void
heap_tuple_toast_attrs(Relation rel, HeapTuple newtup, HeapTuple oldtup)
{
	if (newtup == NULL)
		toast_delete(rel, oldtup);
	else
		toast_insert_or_update(rel, newtup, oldtup);
}


/* ----------
 * heap_tuple_fetch_attr -
 *
 *	Public entry point to get back a toasted value
 *	external storage (possibly still in compressed format).
 * ----------
 */
varattrib *
heap_tuple_fetch_attr(varattrib *attr)
{
	varattrib  *result;

	if (VARATT_IS_EXTERNAL(attr))
	{
		/*
		 * This is an external stored plain value
		 */
		result = toast_fetch_datum(attr);
	}
	else
	{
		/*
		 * This is a plain value inside of the main tuple - why am I
		 * called?
		 */
		result = attr;
	}

	return result;
}


/* ----------
 * heap_tuple_untoast_attr -
 *
 *	Public entry point to get back a toasted value from compression
 *	or external storage.
 * ----------
 */
varattrib *
heap_tuple_untoast_attr(varattrib *attr)
{
	varattrib  *result;

	if (VARATT_IS_EXTERNAL(attr))
	{
		if (VARATT_IS_COMPRESSED(attr))
		{
			/* ----------
			 * This is an external stored compressed value
			 * Fetch it from the toast heap and decompress.
			 * ----------
			 */
			varattrib  *tmp;

			tmp = toast_fetch_datum(attr);
			result = (varattrib *) palloc(attr->va_content.va_external.va_rawsize
										  + VARHDRSZ);
			VARATT_SIZEP(result) = attr->va_content.va_external.va_rawsize
				+ VARHDRSZ;
			pglz_decompress((PGLZ_Header *) tmp, VARATT_DATA(result));

			pfree(tmp);
		}
		else
		{
			/*
			 * This is an external stored plain value
			 */
			result = toast_fetch_datum(attr);
		}
	}
	else if (VARATT_IS_COMPRESSED(attr))
	{
		/*
		 * This is a compressed value inside of the main tuple
		 */
		result = (varattrib *) palloc(attr->va_content.va_compressed.va_rawsize
									  + VARHDRSZ);
		VARATT_SIZEP(result) = attr->va_content.va_compressed.va_rawsize
			+ VARHDRSZ;
		pglz_decompress((PGLZ_Header *) attr, VARATT_DATA(result));
	}
	else

		/*
		 * This is a plain value inside of the main tuple - why am I
		 * called?
		 */
		return attr;

	return result;
}


/* ----------
 * heap_tuple_untoast_attr_slice -
 *
 *		Public entry point to get back part of a toasted value
 *		from compression or external storage.
 * ----------
 */
varattrib *
heap_tuple_untoast_attr_slice(varattrib *attr, int32 sliceoffset, int32 slicelength)
{
	varattrib  *preslice;
	varattrib  *result;
	int32		attrsize;

	if (VARATT_IS_COMPRESSED(attr))
	{
		varattrib  *tmp;

		if (VARATT_IS_EXTERNAL(attr))
			tmp = toast_fetch_datum(attr);
		else
		{
			tmp = attr;			/* compressed in main tuple */
		}

		preslice = (varattrib *) palloc(attr->va_content.va_external.va_rawsize
										+ VARHDRSZ);
		VARATT_SIZEP(preslice) = attr->va_content.va_external.va_rawsize + VARHDRSZ;
		pglz_decompress((PGLZ_Header *) tmp, VARATT_DATA(preslice));

		if (tmp != attr)
			pfree(tmp);
	}
	else
	{
		/* Plain value */
		if (VARATT_IS_EXTERNAL(attr))
		{
			/* fast path */
			return (toast_fetch_datum_slice(attr, sliceoffset, slicelength));
		}
		else
			preslice = attr;
	}

	/* slicing of datum for compressed cases and plain value */

	attrsize = VARSIZE(preslice) - VARHDRSZ;
	if (sliceoffset >= attrsize)
	{
		sliceoffset = 0;
		slicelength = 0;
	}

	if (((sliceoffset + slicelength) > attrsize) || slicelength < 0)
		slicelength = attrsize - sliceoffset;

	result = (varattrib *) palloc(slicelength + VARHDRSZ);
	VARATT_SIZEP(result) = slicelength + VARHDRSZ;

	memcpy(VARDATA(result), VARDATA(preslice) + sliceoffset, slicelength);

	if (preslice != attr)
		pfree(preslice);

	return result;
}


/* ----------
 * toast_raw_datum_size -
 *
 *	Return the raw (detoasted) size of a varlena datum
 * ----------
 */
Size
toast_raw_datum_size(Datum value)
{
	varattrib  *attr = (varattrib *) DatumGetPointer(value);
	Size		result;

	if (VARATT_IS_COMPRESSED(attr))
	{
		/*
		 * va_rawsize shows the original data size, whether the datum is
		 * external or not.
		 */
		result = attr->va_content.va_compressed.va_rawsize + VARHDRSZ;
	}
	else if (VARATT_IS_EXTERNAL(attr))
	{
		/*
		 * an uncompressed external attribute has rawsize including the
		 * header (not too consistent!)
		 */
		result = attr->va_content.va_external.va_rawsize;
	}
	else
	{
		/* plain untoasted datum */
		result = VARSIZE(attr);
	}
	return result;
}


/* ----------
 * toast_delete -
 *
 *	Cascaded delete toast-entries on DELETE
 * ----------
 */
static void
toast_delete(Relation rel, HeapTuple oldtup)
{
	TupleDesc	tupleDesc;
	Form_pg_attribute *att;
	int			numAttrs;
	int			i;
	Datum		value;
	bool		isnull;

	/*
	 * Get the tuple descriptor, the number of and attribute descriptors.
	 */
	tupleDesc = rel->rd_att;
	numAttrs = tupleDesc->natts;
	att = tupleDesc->attrs;

	/*
	 * Check for external stored attributes and delete them from the
	 * secondary relation.
	 */
	for (i = 0; i < numAttrs; i++)
	{
		if (att[i]->attlen == -1)
		{
			value = heap_getattr(oldtup, i + 1, tupleDesc, &isnull);
			if (!isnull && VARATT_IS_EXTERNAL(value))
				toast_delete_datum(rel, value);
		}
	}
}


/* ----------
 * toast_insert_or_update -
 *
 *	Delete no-longer-used toast-entries and create new ones to
 *	make the new tuple fit on INSERT or UPDATE
 * ----------
 */
static void
toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup)
{
	TupleDesc	tupleDesc;
	Form_pg_attribute *att;
	int			numAttrs;
	int			i;
	bool		old_isnull;
	bool		new_isnull;

	bool		need_change = false;
	bool		need_free = false;
	bool		need_delold = false;
	bool		has_nulls = false;

	Size		maxDataLen;

	char		toast_action[MaxHeapAttributeNumber];
	char		toast_nulls[MaxHeapAttributeNumber];
	Datum		toast_values[MaxHeapAttributeNumber];
	int32		toast_sizes[MaxHeapAttributeNumber];
	bool		toast_free[MaxHeapAttributeNumber];
	bool		toast_delold[MaxHeapAttributeNumber];

	/*
	 * Get the tuple descriptor, the number of and attribute descriptors
	 * and the location of the tuple values.
	 */
	tupleDesc = rel->rd_att;
	numAttrs = tupleDesc->natts;
	att = tupleDesc->attrs;

	/* ----------
	 * Then collect information about the values given
	 *
	 * NOTE: toast_action[i] can have these values:
	 *		' '		default handling
	 *		'p'		already processed --- don't touch it
	 *		'x'		incompressible, but OK to move off
	 * ----------
	 */
	memset(toast_action, ' ', numAttrs * sizeof(char));
	memset(toast_nulls, ' ', numAttrs * sizeof(char));
	memset(toast_free, 0, numAttrs * sizeof(bool));
	memset(toast_delold, 0, numAttrs * sizeof(bool));
	for (i = 0; i < numAttrs; i++)
	{
		varattrib  *old_value;
		varattrib  *new_value;

		if (oldtup != NULL)
		{
			/*
			 * For UPDATE get the old and new values of this attribute
			 */
			old_value = (varattrib *) DatumGetPointer(
					heap_getattr(oldtup, i + 1, tupleDesc, &old_isnull));
			toast_values[i] =
				heap_getattr(newtup, i + 1, tupleDesc, &new_isnull);
			new_value = (varattrib *) DatumGetPointer(toast_values[i]);

			/*
			 * If the old value is an external stored one, check if it has
			 * changed so we have to delete it later.
			 */
			if (!old_isnull && att[i]->attlen == -1 &&
				VARATT_IS_EXTERNAL(old_value))
			{
				if (new_isnull || !VARATT_IS_EXTERNAL(new_value) ||
					old_value->va_content.va_external.va_valueid !=
					new_value->va_content.va_external.va_valueid ||
					old_value->va_content.va_external.va_toastrelid !=
					new_value->va_content.va_external.va_toastrelid)
				{
					/*
					 * The old external store value isn't needed any more
					 * after the update
					 */
					toast_delold[i] = true;
					need_delold = true;
				}
				else
				{
					/*
					 * This attribute isn't changed by this update so we
					 * reuse the original reference to the old value in
					 * the new tuple.
					 */
					toast_action[i] = 'p';
					toast_sizes[i] = VARATT_SIZE(toast_values[i]);
					continue;
				}
			}
		}
		else
		{
			/*
			 * For INSERT simply get the new value
			 */
			toast_values[i] =
				heap_getattr(newtup, i + 1, tupleDesc, &new_isnull);
		}

		/*
		 * Handle NULL attributes
		 */
		if (new_isnull)
		{
			toast_action[i] = 'p';
			toast_nulls[i] = 'n';
			has_nulls = true;
			continue;
		}

		/*
		 * Now look at varsize attributes
		 */
		if (att[i]->attlen == -1)
		{
			/*