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a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
120 lines
3.5 KiB
C
120 lines
3.5 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, PostgreSQL Development Team
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*
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* $Id: tuptoaster.h,v 1.11 2001/05/07 00:43:24 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/heapam.h"
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#include "access/htup.h"
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#include "access/tupmacs.h"
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#include "utils/rel.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 and
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* alignment-padding overhead.
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*
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* The numbers need not be the same, though they currently are.
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*/
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#define TOAST_TUPLE_THRESHOLD (MaxTupleSize / 4)
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#define TOAST_TUPLE_TARGET (MaxTupleSize / 4)
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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_formtuple().
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*/
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#define TOAST_INDEX_TARGET (MaxTupleSize / 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) is no more than MaxTupleSize
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* bytes. It *should* be small enough to make toast-table tuples no more
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* than TOAST_TUPLE_THRESHOLD bytes, else heapam.c will uselessly invoke
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* the toaster on toast-table tuples.
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*
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* NB: you cannot change this value without forcing initdb, at least not
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* if your DB contains any multi-chunk toasted values.
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*/
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#define TOAST_MAX_CHUNK_SIZE (TOAST_TUPLE_THRESHOLD - \
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MAXALIGN( \
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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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* heap_tuple_toast_attrs() -
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*
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* Called by heap_insert(), heap_update() and heap_delete().
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* Outdates any no-longer-needed toast entries referenced
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* by oldtup and creates new ones until newtup is no more than
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* TOAST_TUPLE_TARGET (or we run out of toastable values).
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* Possibly modifies newtup by replacing the t_data part!
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*
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* oldtup is NULL if insert, newtup is NULL if delete.
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* ----------
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*/
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extern void heap_tuple_toast_attrs(Relation rel,
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HeapTuple newtup, 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 varattrib *heap_tuple_fetch_attr(varattrib *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 varattrib *heap_tuple_untoast_attr(varattrib *attr);
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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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#endif /* TUPTOASTER_H */
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