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/*------------------------------------------------------------------------- * * tuptoaster.h * POSTGRES definitions for external and compressed storage * of variable size attributes. * * Copyright (c) 2000-2012, PostgreSQL Global Development Group * * src/include/access/tuptoaster.h * *------------------------------------------------------------------------- */ #ifndef TUPTOASTER_H #define TUPTOASTER_H #include "access/htup.h" #include "utils/relcache.h" /* * This enables de-toasting of index entries. Needed until VACUUM is * smart enough to rebuild indexes from scratch. */ #define TOAST_INDEX_HACK /* * Find the maximum size of a tuple if there are to be N tuples per page. */ #define MaximumBytesPerTuple(tuplesPerPage) \ MAXALIGN_DOWN((BLCKSZ - \ MAXALIGN(SizeOfPageHeaderData + (tuplesPerPage) * sizeof(ItemIdData))) \ / (tuplesPerPage)) /* * These symbols control toaster activation. If a tuple is larger than * TOAST_TUPLE_THRESHOLD, we will try to toast it down to no more than * TOAST_TUPLE_TARGET bytes through compressing compressible fields and * moving EXTENDED and EXTERNAL data out-of-line. * * The numbers need not be the same, though they currently are. It doesn't * make sense for TARGET to exceed THRESHOLD, but it could be useful to make * it be smaller. * * Currently we choose both values to match the largest tuple size for which * TOAST_TUPLES_PER_PAGE tuples can fit on a heap page. * * XXX while these can be modified without initdb, some thought needs to be * given to needs_toast_table() in toasting.c before unleashing random * changes. Also see LOBLKSIZE in large_object.h, which can *not* be * changed without initdb. */ #define TOAST_TUPLES_PER_PAGE 4 #define TOAST_TUPLE_THRESHOLD MaximumBytesPerTuple(TOAST_TUPLES_PER_PAGE) #define TOAST_TUPLE_TARGET TOAST_TUPLE_THRESHOLD /* * The code will also consider moving MAIN data out-of-line, but only as a * last resort if the previous steps haven't reached the target tuple size. * In this phase we use a different target size, currently equal to the * largest tuple that will fit on a heap page. This is reasonable since * the user has told us to keep the data in-line if at all possible. */ #define TOAST_TUPLES_PER_PAGE_MAIN 1 #define TOAST_TUPLE_TARGET_MAIN MaximumBytesPerTuple(TOAST_TUPLES_PER_PAGE_MAIN) /* * If an index value is larger than TOAST_INDEX_TARGET, we will try to * compress it (we can't move it out-of-line, however). Note that this * number is per-datum, not per-tuple, for simplicity in index_form_tuple(). */ #define TOAST_INDEX_TARGET (MaxHeapTupleSize / 16) /* * When we store an oversize datum externally, we divide it into chunks * containing at most TOAST_MAX_CHUNK_SIZE data bytes. This number *must* * be small enough that the completed toast-table tuple (including the * ID and sequence fields and all overhead) will fit on a page. * The coding here sets the size on the theory that we want to fit * EXTERN_TUPLES_PER_PAGE tuples of maximum size onto a page. * * NB: Changing TOAST_MAX_CHUNK_SIZE requires an initdb. */ #define EXTERN_TUPLES_PER_PAGE 4 /* tweak only this */ #define EXTERN_TUPLE_MAX_SIZE MaximumBytesPerTuple(EXTERN_TUPLES_PER_PAGE) #define TOAST_MAX_CHUNK_SIZE \ (EXTERN_TUPLE_MAX_SIZE - \ MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) - \ sizeof(Oid) - \ sizeof(int32) - \ VARHDRSZ) /* ---------- * toast_insert_or_update - * * Called by heap_insert() and heap_update(). * ---------- */ extern HeapTuple toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup, int options); /* ---------- * toast_delete - * * Called by heap_delete(). * ---------- */ extern void toast_delete(Relation rel, HeapTuple oldtup); /* ---------- * heap_tuple_fetch_attr() - * * Fetches an external stored attribute from the toast * relation. Does NOT decompress it, if stored external * in compressed format. * ---------- */ extern struct varlena *heap_tuple_fetch_attr(struct varlena * attr); /* ---------- * heap_tuple_untoast_attr() - * * Fully detoasts one attribute, fetching and/or decompressing * it as needed. * ---------- */ extern struct varlena *heap_tuple_untoast_attr(struct varlena * attr); /* ---------- * heap_tuple_untoast_attr_slice() - * * Fetches only the specified portion of an attribute. * (Handles all cases for attribute storage) * ---------- */ extern struct varlena *heap_tuple_untoast_attr_slice(struct varlena * attr, int32 sliceoffset, int32 slicelength); /* ---------- * toast_flatten_tuple - * * "Flatten" a tuple to contain no out-of-line toasted fields. * (This does not eliminate compressed or short-header datums.) * ---------- */ extern HeapTuple toast_flatten_tuple(HeapTuple tup, TupleDesc tupleDesc); /* ---------- * toast_flatten_tuple_to_datum - * * "Flatten" a tuple containing out-of-line toasted fields into a Datum. * ---------- */ extern Datum toast_flatten_tuple_to_datum(HeapTupleHeader tup, uint32 tup_len, TupleDesc tupleDesc); /* ---------- * toast_compress_datum - * * Create a compressed version of a varlena datum, if possible * ---------- */ extern Datum toast_compress_datum(Datum value); /* ---------- * toast_raw_datum_size - * * Return the raw (detoasted) size of a varlena datum * ---------- */ extern Size toast_raw_datum_size(Datum value); /* ---------- * toast_datum_size - * * Return the storage size of a varlena datum * ---------- */ extern Size toast_datum_size(Datum value); #endif /* TUPTOASTER_H */