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First cut at making useful selectivity estimates for range queries

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(ie, WHERE x > lowbound AND x < highbound).  It's not very bright yet
but it does something useful.  Also, rename intltsel/intgtsel to
scalarltsel/scalargtsel to reflect usage better.  Extend convert_to_scalar
to do something a little bit useful with string data types.  Still need
to make it do something with date/time datatypes, but I'll wait for
Thomas's datetime unification dust to settle first.  Eventually the
routine ought not have any type-specific knowledge at all; it ought to
be calling a type-dependent routine found via a pg_type column; but
that's a task for another day.
This commit is contained in:
Tom Lane
2000-01-24 07:16:52 +00:00
parent 8bcac56086
commit 0dbffa704a
9 changed files with 529 additions and 248 deletions
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245
src/backend/optimizer/path/clausesel.c
View File

@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/clausesel.c,v 1.28 2000/01/23 02:06:58 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/clausesel.c,v 1.29 2000/01/24 07:16:46 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -23,6 +23,23 @@
#include "utils/lsyscache.h"
/*
* Data structure for accumulating info about possible range-query
* clause pairs in clauselist_selectivity.
*/
typedef struct RangeQueryClause {
struct RangeQueryClause *next; /* next in linked list */
Node *var; /* The common variable of the clauses */
bool have_lobound; /* found a low-bound clause yet? */
bool have_hibound; /* found a high-bound clause yet? */
Selectivity lobound; /* Selectivity of a var > something clause */
Selectivity hibound; /* Selectivity of a var < something clause */
} RangeQueryClause;
static void addRangeClause(RangeQueryClause **rqlist, Node *clause,
int flag, bool isLTsel, Selectivity s2);
/****************************************************************************
* ROUTINES TO COMPUTE SELECTIVITIES
****************************************************************************/
@@ -55,29 +72,237 @@ restrictlist_selectivity(Query *root,
* must be returned.
*
* See clause_selectivity() for the meaning of the varRelid parameter.
*
* Our basic approach is to take the product of the selectivities of the
* subclauses. However, that's only right if the subclauses have independent
* probabilities, and in reality they are often NOT independent. So,
* we want to be smarter where we can.
* Currently, the only extra smarts we have is to recognize "range queries",
* such as "x > 34 AND x < 42". Clauses are recognized as possible range
* query components if they are restriction opclauses whose operators have
* scalarltsel() or scalargtsel() as their restriction selectivity estimator.
* We pair up clauses of this form that refer to the same variable. An
* unpairable clause of this kind is simply multiplied into the selectivity
* product in the normal way. But when we find a pair, we know that the
* selectivities represent the relative positions of the low and high bounds
* within the column's range, so instead of figuring the selectivity as
* hisel * losel, we can figure it as hisel + losel - 1. (To visualize this,
* see that hisel is the fraction of the range below the high bound, while
* losel is the fraction above the low bound; so hisel can be interpreted
* directly as a 0..1 value but we need to convert losel to 1-losel before
* interpreting it as a value. Then the available range is 1-losel to hisel.)
* If the calculation yields zero or negative, however, we chicken out and
* use the default interpretation; that probably means that one or both
* selectivities is a default estimate rather than an actual range value.
* Of course this is all very dependent on the behavior of
* scalarltsel/scalargtsel; perhaps some day we can generalize the approach.
*/
Selectivity
clauselist_selectivity(Query *root,
List *clauses,
int varRelid)
{
Selectivity s1 = 1.0;
List *clause;
Selectivity s1 = 1.0;
RangeQueryClause *rqlist = NULL;
List *clist;
/* Use the product of the selectivities of the subclauses.
* XXX this is too optimistic, since the subclauses
* are very likely not independent...
/*
* Initial scan over clauses. Anything that doesn't look like a
* potential rangequery clause gets multiplied into s1 and forgotten.
* Anything that does gets inserted into an rqlist entry.
*/
foreach(clause, clauses)
foreach(clist, clauses)
{
Selectivity s2 = clause_selectivity(root,
(Node *) lfirst(clause),
varRelid);
Node *clause = (Node *) lfirst(clist);
Selectivity s2;
/*
* See if it looks like a restriction clause with a constant.
* (If it's not a constant we can't really trust the selectivity!)
* NB: for consistency of results, this fragment of code had
* better match what clause_selectivity() would do.
*/
if (varRelid != 0 || NumRelids(clause) == 1)
{
int relidx;
AttrNumber attno;
Datum constval;
int flag;
get_relattval(clause, varRelid,
&relidx, &attno, &constval, &flag);
if (relidx != 0 && (flag & SEL_CONSTANT))
{
/* if get_relattval succeeded, it must be an opclause */
Oid opno = ((Oper *) ((Expr *) clause)->oper)->opno;
RegProcedure oprrest = get_oprrest(opno);
if (!oprrest)
s2 = (Selectivity) 0.5;
else
s2 = restriction_selectivity(oprrest, opno,
getrelid(relidx,
root->rtable),
attno,
constval, flag);
/*
* If we reach here, we have computed the same result
* that clause_selectivity would, so we can just use s2
* if it's the wrong oprrest. But if it's the right
* oprrest, add the clause to rqlist for later processing.
*/
switch (oprrest)
{
case F_SCALARLTSEL:
addRangeClause(&rqlist, clause, flag, true, s2);
break;
case F_SCALARGTSEL:
addRangeClause(&rqlist, clause, flag, false, s2);
break;
default:
/* Just merge the selectivity in generically */
s1 = s1 * s2;
break;
}
continue; /* drop to loop bottom */
}
}
/* Not the right form, so treat it generically. */
s2 = clause_selectivity(root, clause, varRelid);
s1 = s1 * s2;
}
/*
* Now scan the rangequery pair list.
*/
while (rqlist != NULL)
{
RangeQueryClause *rqnext;
if (rqlist->have_lobound && rqlist->have_hibound)
{
/* Successfully matched a pair of range clauses */
Selectivity s2 = rqlist->hibound + rqlist->lobound - 1.0;
if (s2 > 0.0)
{
/* All our hard work has paid off! */
s1 *= s2;
}
else
{
/* One or both is probably a default estimate,
* so punt and just merge them in generically.
*/
s1 *= rqlist->hibound * rqlist->lobound;
}
}
else
{
/* Only found one of a pair, merge it in generically */
if (rqlist->have_lobound)
s1 *= rqlist->lobound;
else
s1 *= rqlist->hibound;
}
/* release storage and advance */
rqnext = rqlist->next;
pfree(rqlist);
rqlist = rqnext;
}
return s1;
}
/*
* addRangeClause --- add a new range clause for clauselist_selectivity
*
* Here is where we try to match up pairs of range-query clauses
*/
static void
addRangeClause(RangeQueryClause **rqlist, Node *clause,
int flag, bool isLTsel, Selectivity s2)
{
RangeQueryClause *rqelem;
Node *var;
bool is_lobound;
/* get_relattval sets flag&SEL_RIGHT if the var is on the LEFT. */
if (flag & SEL_RIGHT)
{
var = (Node *) get_leftop((Expr *) clause);
is_lobound = ! isLTsel; /* x < something is high bound */
}
else
{
var = (Node *) get_rightop((Expr *) clause);
is_lobound = isLTsel; /* something < x is low bound */
}
for (rqelem = *rqlist; rqelem; rqelem = rqelem->next)
{
/* We use full equal() here because the "var" might be a function
* of one or more attributes of the same relation...
*/
if (! equal(var, rqelem->var))
continue;
/* Found the right group to put this clause in */
if (is_lobound)
{
if (! rqelem->have_lobound)
{
rqelem->have_lobound = true;
rqelem->lobound = s2;
}
else
{
/* We have found two similar clauses, such as
* x < y AND x < z. Keep only the more restrictive one.
*/
if (rqelem->lobound > s2)
rqelem->lobound = s2;
}
}
else
{
if (! rqelem->have_hibound)
{
rqelem->have_hibound = true;
rqelem->hibound = s2;
}
else
{
/* We have found two similar clauses, such as
* x > y AND x > z. Keep only the more restrictive one.
*/
if (rqelem->hibound > s2)
rqelem->hibound = s2;
}
}
return;
}
/* No matching var found, so make a new clause-pair data structure */
rqelem = (RangeQueryClause *) palloc(sizeof(RangeQueryClause));
rqelem->var = var;
if (is_lobound)
{
rqelem->have_lobound = true;
rqelem->have_hibound = false;
rqelem->lobound = s2;
}
else
{
rqelem->have_lobound = false;
rqelem->have_hibound = true;
rqelem->hibound = s2;
}
rqelem->next = *rqlist;
*rqlist = rqelem;
}
/*
* clause_selectivity -
* Compute the selectivity of a general boolean expression clause.

176
src/backend/utils/adt/selfuncs.c
View File

@@ -14,7 +14,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.52 2000/01/24 02:12:55 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.53 2000/01/24 07:16:46 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -47,15 +47,13 @@
/* default selectivity estimate for inequalities such as "A < b" */
#define DEFAULT_INEQ_SEL (1.0 / 3.0)
static bool convert_to_scale(Datum value, Oid typid,
double *scaleval);
static void getattproperties(Oid relid, AttrNumber attnum,
Oid *typid,
int *typlen,
bool *typbyval,
int32 *typmod);
static bool getattstatistics(Oid relid, AttrNumber attnum,
Oid opid, Oid typid, int32 typmod,
Oid typid, int32 typmod,
double *nullfrac,
double *commonfrac,
Datum *commonval,
@@ -100,7 +98,7 @@ eqsel(Oid opid,
&typid, &typlen, &typbyval, &typmod);
/* get stats for the attribute, if available */
if (getattstatistics(relid, attno, opid, typid, typmod,
if (getattstatistics(relid, attno, typid, typmod,
&nullfrac, &commonfrac, &commonval,
NULL, NULL))
{
@@ -212,19 +210,18 @@ neqsel(Oid opid,
}
/*
* intltsel - Selectivity of "<" (also "<=") for integers.
* scalarltsel - Selectivity of "<" (also "<=") for scalars.
*
* Actually, this works and is used for all numeric types, so it should
* be renamed. In fact, it is also currently called for all manner of
* non-numeric types, for which it is NOT very helpful. That needs
* to be fixed.
* This routine works for any datatype (or pair of datatypes) known to
* convert_to_scalar(). If it is applied to some other datatype,
* it will return a default estimate.
*/
float64
intltsel(Oid opid,
Oid relid,
AttrNumber attno,
Datum value,
int32 flag)
scalarltsel(Oid opid,
Oid relid,
AttrNumber attno,
Datum value,
int32 flag)
{
float64 result;
@@ -253,19 +250,19 @@ intltsel(Oid opid,
*/
oprtuple = get_operator_tuple(opid);
if (! HeapTupleIsValid(oprtuple))
elog(ERROR, "intltsel: no tuple for operator %u", opid);
elog(ERROR, "scalarltsel: no tuple for operator %u", opid);
ltype = ((Form_pg_operator) GETSTRUCT(oprtuple))->oprleft;
rtype = ((Form_pg_operator) GETSTRUCT(oprtuple))->oprright;
/* Convert the constant to a uniform comparison scale. */
if (! convert_to_scale(value,
((flag & SEL_RIGHT) ? rtype : ltype),
&val))
if (! convert_to_scalar(value,
((flag & SEL_RIGHT) ? rtype : ltype),
&val))
{
/* Ideally we'd produce an error here, on the grounds that
* the given operator shouldn't have intltsel registered as its
/* Ideally we'd produce an error here, on the grounds that the
* given operator shouldn't have scalarltsel registered as its
* selectivity func unless we can deal with its operand types.
* But currently, all manner of stuff is invoking intltsel,
* But currently, all manner of stuff is invoking scalarltsel,
* so give a default estimate until that can be fixed.
*/
*result = DEFAULT_INEQ_SEL;
@@ -276,7 +273,7 @@ intltsel(Oid opid,
getattproperties(relid, attno,
&typid, &typlen, &typbyval, &typmod);
if (! getattstatistics(relid, attno, opid, typid, typmod,
if (! getattstatistics(relid, attno, typid, typmod,
NULL, NULL, NULL,
&loval, &hival))
{
@@ -286,8 +283,8 @@ intltsel(Oid opid,
}
/* Convert the attribute's loval/hival to common scale. */
if (! convert_to_scale(loval, typid, &low) ||
! convert_to_scale(hival, typid, &high))
if (! convert_to_scalar(loval, typid, &low) ||
! convert_to_scalar(hival, typid, &high))
{
/* See above comments... */
if (! typbyval)
@@ -341,23 +338,23 @@ intltsel(Oid opid,
}
/*
* intgtsel - Selectivity of ">" (also ">=") for integers.
* scalargtsel - Selectivity of ">" (also ">=") for integers.
*
* See above comments for intltsel.
* See above comments for scalarltsel.
*/
float64
intgtsel(Oid opid,
Oid relid,
AttrNumber attno,
Datum value,
int32 flag)
scalargtsel(Oid opid,
Oid relid,
AttrNumber attno,
Datum value,
int32 flag)
{
float64 result;
/* Compute selectivity of "<", then invert --- but only if we
* were able to produce a non-default estimate.
*/
result = intltsel(opid, relid, attno, value, flag);
result = scalarltsel(opid, relid, attno, value, flag);
if (*result != DEFAULT_INEQ_SEL)
*result = 1.0 - *result;
return result;
@@ -429,14 +426,14 @@ neqjoinsel(Oid opid,
}
/*
* intltjoinsel - Join selectivity of "<" and "<="
* scalarltjoinsel - Join selectivity of "<" and "<=" for scalars
*/
float64
intltjoinsel(Oid opid,
Oid relid1,
AttrNumber attno1,
Oid relid2,
AttrNumber attno2)
scalarltjoinsel(Oid opid,
Oid relid1,
AttrNumber attno1,
Oid relid2,
AttrNumber attno2)
{
float64 result;
@@ -446,14 +443,14 @@ intltjoinsel(Oid opid,
}
/*
* intgtjoinsel - Join selectivity of ">" and ">="
* scalargtjoinsel - Join selectivity of ">" and ">=" for scalars
*/
float64
intgtjoinsel(Oid opid,
Oid relid1,
AttrNumber attno1,
Oid relid2,
AttrNumber attno2)
scalargtjoinsel(Oid opid,
Oid relid1,
AttrNumber attno1,
Oid relid2,
AttrNumber attno2)
{
float64 result;
@@ -463,21 +460,25 @@ intgtjoinsel(Oid opid,
}
/*
* convert_to_scale
* Convert a given value of the indicated type to the comparison
* scale needed by intltsel(). Returns "true" if successful.
* convert_to_scalar
* Convert a non-NULL value of the indicated type to the comparison
* scale needed by scalarltsel()/scalargtsel().
* Returns "true" if successful.
*
* All numeric datatypes are simply converted to their equivalent
* "double" values.
* Future extension: convert string-like types to some suitable scale.
* "double" values. String datatypes are converted to a crude scale
* using their first character (only if it is in the ASCII range,
* to try to avoid problems with non-ASCII collating sequences).
*/
static bool
convert_to_scale(Datum value, Oid typid,
double *scaleval)
bool
convert_to_scalar(Datum value, Oid typid,
double *scaleval)
{
/* Fast-path conversions for some built-in types */
switch (typid)
{
/*
* Built-in numeric types
*/
case BOOLOID:
*scaleval = (double) DatumGetUInt8(value);
return true;
@@ -504,18 +505,54 @@ convert_to_scale(Datum value, Oid typid,
/* we can treat OIDs as integers... */
*scaleval = (double) DatumGetObjectId(value);
return true;
case TEXTOID:
/*
* Eventually this should get handled by somehow scaling as a
* string value. For now, we need to call it out to avoid
* falling into the default case, because there is a float8(text)
* function declared in pg_proc that will do the wrong thing :-(
*/
/*
* Built-in string types
*/
case CHAROID:
{
char ch = DatumGetChar(value);
if (ch >= 0 && ch < 127)
{
*scaleval = (double) ch;
return true;
}
break;
}
case BPCHAROID:
case VARCHAROID:
case TEXTOID:
if (VARSIZE(DatumGetPointer(value)) > VARHDRSZ)
{
char ch = * (char *) VARDATA(DatumGetPointer(value));
if (ch >= 0 && ch < 127)
{
*scaleval = (double) ch;
return true;
}
}
break;
case NAMEOID:
{
NameData *nm = (NameData *) DatumGetPointer(value);
char ch = NameStr(*nm)[0];
if (ch >= 0 && ch < 127)
{
*scaleval = (double) ch;
return true;
}
break;
}
default:
{
/* See whether there is a registered type-conversion function,
/*
* See whether there is a registered type-conversion function,
* namely a procedure named "float8" with the right signature.
* If so, assume we can convert the value to the numeric scale.
*/
Oid oid_array[FUNC_MAX_ARGS];
HeapTuple ftup;
@@ -589,7 +626,9 @@ getattproperties(Oid relid, AttrNumber attnum,
* after use if the data type is not by-value.)
*/
static bool
getattstatistics(Oid relid, AttrNumber attnum, Oid opid, Oid typid,
getattstatistics(Oid relid,
AttrNumber attnum,
Oid typid,
int32 typmod,
double *nullfrac,
double *commonfrac,
@@ -603,8 +642,15 @@ getattstatistics(Oid relid, AttrNumber attnum, Oid opid, Oid typid,
Oid typelem;
bool isnull;
/* We assume that there will only be one entry in pg_statistic
* for the given rel/att. Someday, VACUUM might store more than one...
/*
* We assume that there will only be one entry in pg_statistic for
* the given rel/att, so we search WITHOUT considering the staop
* column. Someday, VACUUM might store more than one entry per rel/att,
* corresponding to more than one possible sort ordering defined for
* the column type. However, to make that work we will need to figure
* out which staop to search for --- it's not necessarily the one we
* have at hand! (For example, we might have a '>' operator rather than
* the '<' operator that will appear in staop.)
*/
tuple = SearchSysCacheTuple(STATRELID,
ObjectIdGetDatum(relid),