216 lines
8.2 KiB
C
216 lines
8.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_statistic.h
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* definition of the system "statistic" relation (pg_statistic)
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* along with the relation's initial contents.
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*
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*
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* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/pg_statistic.h,v 1.23 2003/11/29 22:40:58 pgsql Exp $
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*
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* NOTES
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* the genbki.sh script reads this file and generates .bki
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* information from the DATA() statements.
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_STATISTIC_H
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#define PG_STATISTIC_H
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/* ----------------
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* postgres.h contains the system type definitions and the
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* CATALOG(), BOOTSTRAP and DATA() sugar words so this file
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* can be read by both genbki.sh and the C compiler.
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* ----------------
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*/
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/*
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* Keep C compiler happy with anyarray, below. This will need to go elsewhere
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* if we ever use anyarray for more than pg_statistic.
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*/
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typedef struct varlena anyarray;
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/* ----------------
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* pg_statistic definition. cpp turns this into
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* typedef struct FormData_pg_statistic
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* ----------------
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*/
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CATALOG(pg_statistic) BKI_WITHOUT_OIDS
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{
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/* These fields form the unique key for the entry: */
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Oid starelid; /* relation containing attribute */
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int2 staattnum; /* attribute (column) stats are for */
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/* the fraction of the column's entries that are NULL: */
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float4 stanullfrac;
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/*
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* stawidth is the average width in bytes of non-null entries. For
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* fixed-width datatypes this is of course the same as the typlen, but
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* for var-width types it is more useful. Note that this is the
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* average width of the data as actually stored, post-TOASTing (eg,
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* for a moved-out-of-line value, only the size of the pointer object
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* is counted). This is the appropriate definition for the primary
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* use of the statistic, which is to estimate sizes of in-memory hash
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* tables of tuples.
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*/
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int4 stawidth;
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/* ----------------
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* stadistinct indicates the (approximate) number of distinct non-null
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* data values in the column. The interpretation is:
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* 0 unknown or not computed
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* > 0 actual number of distinct values
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* < 0 negative of multiplier for number of rows
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* The special negative case allows us to cope with columns that are
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* unique (stadistinct = -1) or nearly so (for example, a column in
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* which values appear about twice on the average could be represented
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* by stadistinct = -0.5). Because the number-of-rows statistic in
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* pg_class may be updated more frequently than pg_statistic is, it's
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* important to be able to describe such situations as a multiple of
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* the number of rows, rather than a fixed number of distinct values.
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* But in other cases a fixed number is correct (eg, a boolean column).
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* ----------------
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*/
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float4 stadistinct;
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/* ----------------
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* To allow keeping statistics on different kinds of datatypes,
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* we do not hard-wire any particular meaning for the remaining
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* statistical fields. Instead, we provide several "slots" in which
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* statistical data can be placed. Each slot includes:
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* kind integer code identifying kind of data
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* op OID of associated operator, if needed
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* numbers float4 array (for statistical values)
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* values text array (for representations of data values)
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* The ID and operator fields are never NULL; they are zeroes in an
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* unused slot. The numbers and values fields are NULL in an unused
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* slot, and might also be NULL in a used slot if the slot kind has
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* no need for one or the other.
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* ----------------
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*/
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int2 stakind1;
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int2 stakind2;
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int2 stakind3;
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int2 stakind4;
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Oid staop1;
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Oid staop2;
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Oid staop3;
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Oid staop4;
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/*
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* THE REST OF THESE ARE VARIABLE LENGTH FIELDS, and may even be
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* absent (NULL). They cannot be accessed as C struct entries; you
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* have to use the full field access machinery (heap_getattr) for
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* them. We declare them here for the catalog machinery.
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*/
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float4 stanumbers1[1];
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float4 stanumbers2[1];
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float4 stanumbers3[1];
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float4 stanumbers4[1];
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/*
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* Values in these arrays are values of the column's data type. We
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* presently have to cheat quite a bit to allow polymorphic arrays of
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* this kind, but perhaps someday it'll be a less bogus facility.
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*/
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anyarray stavalues1;
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anyarray stavalues2;
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anyarray stavalues3;
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anyarray stavalues4;
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} FormData_pg_statistic;
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#define STATISTIC_NUM_SLOTS 4
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/* ----------------
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* Form_pg_statistic corresponds to a pointer to a tuple with
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* the format of pg_statistic relation.
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* ----------------
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*/
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typedef FormData_pg_statistic *Form_pg_statistic;
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/* ----------------
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* compiler constants for pg_statistic
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* ----------------
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*/
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#define Natts_pg_statistic 21
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#define Anum_pg_statistic_starelid 1
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#define Anum_pg_statistic_staattnum 2
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#define Anum_pg_statistic_stanullfrac 3
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#define Anum_pg_statistic_stawidth 4
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#define Anum_pg_statistic_stadistinct 5
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#define Anum_pg_statistic_stakind1 6
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#define Anum_pg_statistic_stakind2 7
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#define Anum_pg_statistic_stakind3 8
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#define Anum_pg_statistic_stakind4 9
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#define Anum_pg_statistic_staop1 10
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#define Anum_pg_statistic_staop2 11
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#define Anum_pg_statistic_staop3 12
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#define Anum_pg_statistic_staop4 13
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#define Anum_pg_statistic_stanumbers1 14
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#define Anum_pg_statistic_stanumbers2 15
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#define Anum_pg_statistic_stanumbers3 16
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#define Anum_pg_statistic_stanumbers4 17
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#define Anum_pg_statistic_stavalues1 18
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#define Anum_pg_statistic_stavalues2 19
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#define Anum_pg_statistic_stavalues3 20
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#define Anum_pg_statistic_stavalues4 21
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/*
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* Currently, three statistical slot "kinds" are defined: most common values,
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* histogram, and correlation. Additional "kinds" will probably appear in
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* future to help cope with non-scalar datatypes.
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*
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* Code reading the pg_statistic relation should not assume that a particular
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* data "kind" will appear in any particular slot. Instead, search the
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* stakind fields to see if the desired data is available.
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*/
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/*
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* In a "most common values" slot, staop is the OID of the "=" operator
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* used to decide whether values are the same or not. stavalues contains
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* the K most common non-null values appearing in the column, and stanumbers
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* contains their frequencies (fractions of total row count). The values
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* shall be ordered in decreasing frequency. Note that since the arrays are
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* variable-size, K may be chosen by the statistics collector. Values should
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* not appear in MCV unless they have been observed to occur more than once;
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* a unique column will have no MCV slot.
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*/
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#define STATISTIC_KIND_MCV 1
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/*
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* A "histogram" slot describes the distribution of scalar data. staop is
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* the OID of the "<" operator that describes the sort ordering. (In theory,
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* more than one histogram could appear, if a datatype has more than one
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* useful sort operator.) stavalues contains M (>=2) non-null values that
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* divide the non-null column data values into M-1 bins of approximately equal
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* population. The first stavalues item is the MIN and the last is the MAX.
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* stanumbers is not used and should be NULL. IMPORTANT POINT: if an MCV
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* slot is also provided, then the histogram describes the data distribution
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* *after removing the values listed in MCV* (thus, it's a "compressed
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* histogram" in the technical parlance). This allows a more accurate
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* representation of the distribution of a column with some very-common
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* values. In a column with only a few distinct values, it's possible that
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* the MCV list describes the entire data population; in this case the
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* histogram reduces to empty and should be omitted.
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*/
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#define STATISTIC_KIND_HISTOGRAM 2
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/*
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* A "correlation" slot describes the correlation between the physical order
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* of table tuples and the ordering of data values of this column, as seen
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* by the "<" operator identified by staop. (As with the histogram, more
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* than one entry could theoretically appear.) stavalues is not used and
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* should be NULL. stanumbers contains a single entry, the correlation
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* coefficient between the sequence of data values and the sequence of
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* their actual tuple positions. The coefficient ranges from +1 to -1.
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*/
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#define STATISTIC_KIND_CORRELATION 3
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#endif /* PG_STATISTIC_H */
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