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-rw-r--r-- | src/include/access/heaptoast.h | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/src/include/access/heaptoast.h b/src/include/access/heaptoast.h new file mode 100644 index 0000000..2635831 --- /dev/null +++ b/src/include/access/heaptoast.h @@ -0,0 +1,149 @@ +/*------------------------------------------------------------------------- + * + * heaptoast.h + * Heap-specific definitions for external and compressed storage + * of variable size attributes. + * + * Copyright (c) 2000-2020, PostgreSQL Global Development Group + * + * src/include/access/heaptoast.h + * + *------------------------------------------------------------------------- + */ +#ifndef HEAPTOAST_H +#define HEAPTOAST_H + +#include "access/htup_details.h" +#include "storage/lockdefs.h" +#include "utils/relcache.h" + +/* + * 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(SizeofHeapTupleHeader) - \ + sizeof(Oid) - \ + sizeof(int32) - \ + VARHDRSZ) + +/* ---------- + * heap_toast_insert_or_update - + * + * Called by heap_insert() and heap_update(). + * ---------- + */ +extern HeapTuple heap_toast_insert_or_update(Relation rel, HeapTuple newtup, + HeapTuple oldtup, int options); + +/* ---------- + * heap_toast_delete - + * + * Called by heap_delete(). + * ---------- + */ +extern void heap_toast_delete(Relation rel, HeapTuple oldtup, + bool is_speculative); + +/* ---------- + * 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_build_flattened_tuple - + * + * Build a tuple containing no out-of-line toasted fields. + * (This does not eliminate compressed or short-header datums.) + * ---------- + */ +extern HeapTuple toast_build_flattened_tuple(TupleDesc tupleDesc, + Datum *values, + bool *isnull); + +/* ---------- + * heap_fetch_toast_slice + * + * Fetch a slice from a toast value stored in a heap table. + * ---------- + */ +extern void heap_fetch_toast_slice(Relation toastrel, Oid valueid, + int32 attrsize, int32 sliceoffset, + int32 slicelength, struct varlena *result); + +#endif /* HEAPTOAST_H */ |