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9d035f4254
SizeOfPageHeaderData instead of sizeof(PageHeaderData) in places where that makes the code clearer, and avoid casting between Page and PageHeader where possible. Zdenek Kotala, with some additional cleanup by Heikki Linnakangas. I did not apply the parts of the proposed patch that would have resulted in slightly changing the on-disk format of hash indexes; it seems to me that's not a win as long as there's any chance of having in-place upgrade for 8.4.
173 lines
5.1 KiB
C
173 lines
5.1 KiB
C
/*-------------------------------------------------------------------------
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*
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* tuptoaster.h
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* POSTGRES definitions for external and compressed storage
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* of variable size attributes.
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*
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* Copyright (c) 2000-2008, PostgreSQL Global Development Group
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*
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* $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.41 2008/07/13 20:45:47 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef TUPTOASTER_H
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#define TUPTOASTER_H
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#include "access/htup.h"
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#include "storage/bufpage.h"
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#include "utils/relcache.h"
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/*
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* This enables de-toasting of index entries. Needed until VACUUM is
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* smart enough to rebuild indexes from scratch.
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*/
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#define TOAST_INDEX_HACK
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/*
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* These symbols control toaster activation. If a tuple is larger than
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* TOAST_TUPLE_THRESHOLD, we will try to toast it down to no more than
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* TOAST_TUPLE_TARGET bytes. Both numbers include all tuple header overhead
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* and between-fields alignment padding, but we do *not* consider any
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* end-of-tuple alignment padding; hence the values can be compared directly
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* to a tuple's t_len field.
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*
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* The numbers need not be the same, though they currently are. It doesn't
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* make sense for TARGET to exceed THRESHOLD, but it could be useful to make
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* it be smaller.
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*
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* Currently we choose both values to match the largest tuple size for which
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* TOAST_TUPLES_PER_PAGE tuples can fit on a disk page.
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*
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* XXX while these can be modified without initdb, some thought needs to be
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* given to needs_toast_table() in toasting.c before unleashing random
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* changes. Also see LOBLKSIZE in large_object.h, which can *not* be
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* changed without initdb.
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*/
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#define TOAST_TUPLES_PER_PAGE 4
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#define TOAST_TUPLE_THRESHOLD \
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MAXALIGN_DOWN((BLCKSZ - \
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MAXALIGN(SizeOfPageHeaderData + TOAST_TUPLES_PER_PAGE * sizeof(ItemIdData))) \
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/ TOAST_TUPLES_PER_PAGE)
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#define TOAST_TUPLE_TARGET TOAST_TUPLE_THRESHOLD
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/*
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* If an index value is larger than TOAST_INDEX_TARGET, we will try to
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* compress it (we can't move it out-of-line, however). Note that this
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* number is per-datum, not per-tuple, for simplicity in index_form_tuple().
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*/
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#define TOAST_INDEX_TARGET (MaxHeapTupleSize / 16)
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/*
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* When we store an oversize datum externally, we divide it into chunks
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* containing at most TOAST_MAX_CHUNK_SIZE data bytes. This number *must*
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* be small enough that the completed toast-table tuple (including the
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* ID and sequence fields and all overhead) will fit on a page.
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* The coding here sets the size on the theory that we want to fit
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* EXTERN_TUPLES_PER_PAGE tuples of maximum size onto a page.
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*
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* NB: Changing TOAST_MAX_CHUNK_SIZE requires an initdb.
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*/
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#define EXTERN_TUPLES_PER_PAGE 4 /* tweak only this */
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#define EXTERN_TUPLE_MAX_SIZE \
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MAXALIGN_DOWN((BLCKSZ - \
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MAXALIGN(SizeOfPageHeaderData + EXTERN_TUPLES_PER_PAGE * sizeof(ItemIdData))) \
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/ EXTERN_TUPLES_PER_PAGE)
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#define TOAST_MAX_CHUNK_SIZE \
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(EXTERN_TUPLE_MAX_SIZE - \
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MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) - \
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sizeof(Oid) - \
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sizeof(int32) - \
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VARHDRSZ)
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/* ----------
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* toast_insert_or_update -
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*
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* Called by heap_insert() and heap_update().
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* ----------
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*/
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extern HeapTuple toast_insert_or_update(Relation rel,
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HeapTuple newtup, HeapTuple oldtup,
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bool use_wal, bool use_fsm);
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/* ----------
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* toast_delete -
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*
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* Called by heap_delete().
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* ----------
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*/
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extern void toast_delete(Relation rel, HeapTuple oldtup);
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/* ----------
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* heap_tuple_fetch_attr() -
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*
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* Fetches an external stored attribute from the toast
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* relation. Does NOT decompress it, if stored external
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* in compressed format.
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* ----------
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*/
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extern struct varlena *heap_tuple_fetch_attr(struct varlena * attr);
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/* ----------
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* heap_tuple_untoast_attr() -
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*
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* Fully detoasts one attribute, fetching and/or decompressing
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* it as needed.
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* ----------
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*/
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extern struct varlena *heap_tuple_untoast_attr(struct varlena * attr);
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/* ----------
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* heap_tuple_untoast_attr_slice() -
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*
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* Fetches only the specified portion of an attribute.
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* (Handles all cases for attribute storage)
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* ----------
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*/
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extern struct varlena *heap_tuple_untoast_attr_slice(struct varlena * attr,
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int32 sliceoffset,
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int32 slicelength);
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/* ----------
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* toast_flatten_tuple_attribute -
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*
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* If a Datum is of composite type, "flatten" it to contain no toasted fields.
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* This must be invoked on any potentially-composite field that is to be
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* inserted into a tuple. Doing this preserves the invariant that toasting
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* goes only one level deep in a tuple.
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* ----------
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*/
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extern Datum toast_flatten_tuple_attribute(Datum value,
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Oid typeId, int32 typeMod);
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/* ----------
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* toast_compress_datum -
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*
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* Create a compressed version of a varlena datum, if possible
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* ----------
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*/
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extern Datum toast_compress_datum(Datum value);
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/* ----------
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* toast_raw_datum_size -
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*
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* Return the raw (detoasted) size of a varlena datum
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* ----------
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*/
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extern Size toast_raw_datum_size(Datum value);
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/* ----------
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* toast_datum_size -
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*
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* Return the storage size of a varlena datum
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* ----------
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*/
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extern Size toast_datum_size(Datum value);
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#endif /* TUPTOASTER_H */
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