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Fix up btree's initial scankey processing to be able to detect redundant

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or contradictory keys even in cross-data-type scenarios.  This is another
benefit of the opfamily rewrite: we can find the needed comparison
operators now.
This commit is contained in:
Tom Lane 2006-12-28 23:16:39 +00:00
parent 3870341d1e
commit 9aefd56669
3 changed files with 209 additions and 100 deletions
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11
src/backend/access/nbtree/README
View File

@ -1,4 +1,4 @@
$PostgreSQL: pgsql/src/backend/access/nbtree/README,v 1.14 2006/11/01 19:43:17 tgl Exp $
$PostgreSQL: pgsql/src/backend/access/nbtree/README,v 1.15 2006/12/28 23:16:39 tgl Exp $
This directory contains a correct implementation of Lehman and Yao's
high-concurrency B-tree management algorithm (P. Lehman and S. Yao,
@ -480,7 +480,8 @@ than key.
Notes to operator class implementors
------------------------------------
With this implementation, we require each supported datatype to supply
us with a comparison procedure via pg_amproc. This procedure must take
two nonnull values A and B and return an int32 < 0, 0, or > 0 if A < B,
A = B, or A > B, respectively. See nbtcompare.c for examples.
With this implementation, we require each supported combination of
datatypes to supply us with a comparison procedure via pg_amproc.
This procedure must take two nonnull values A and B and return an int32 < 0,
0, or > 0 if A < B, A = B, or A > B, respectively. See nbtcompare.c for
examples.

24
src/backend/access/nbtree/nbtsearch.c
View File

@ -8,7 +8,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.108 2006/12/23 00:43:09 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.109 2006/12/28 23:16:39 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -476,16 +476,16 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* attributes to its right, because it would break our simplistic notion
* of what initial positioning strategy to use.
*
* When the scan keys include non-default operators, _bt_preprocess_keys
* When the scan keys include cross-type operators, _bt_preprocess_keys
* may not be able to eliminate redundant keys; in such cases we will
* arbitrarily pick a usable one for each attribute. This is correct
* but possibly not optimal behavior. (For example, with keys like
* "x >= 4 AND x >= 5" we would elect to scan starting at x=4 when
* x=5 would be more efficient.) Since the situation only arises in
* hokily-worded queries, live with it.
* x=5 would be more efficient.) Since the situation only arises given
* a poorly-worded query plus an incomplete opfamily, live with it.
*
* When both equality and inequality keys appear for a single attribute
* (again, only possible when non-default operators appear), we *must*
* (again, only possible when cross-type operators appear), we *must*
* select one of the equality keys for the starting point, because
* _bt_checkkeys() will stop the scan as soon as an equality qual fails.
* For example, if we have keys like "x >= 4 AND x = 10" and we elect to
@ -658,11 +658,15 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
* to an insertion scan key by replacing the sk_func with the
* appropriate btree comparison function.
*
* If scankey operator is of the default type for the index, we
* can use the cached comparison function; otherwise gotta look it
* up in the catalogs. Also, we support the convention that
* sk_subtype == 0 means the default type; this is a hack to
* simplify life for ScanKeyInit().
* If scankey operator is not a cross-type comparison, we can use
* the cached comparison function; otherwise gotta look it up in
* the catalogs. (That can't lead to infinite recursion, since no
* indexscan initiated by syscache lookup will use cross-data-type
* operators.)
*
* We support the convention that sk_subtype == InvalidOid means
* the opclass input type; this is a hack to simplify life for
* ScanKeyInit().
*/
if (cur->sk_subtype == rel->rd_opcintype[i] ||
cur->sk_subtype == InvalidOid)

274
src/backend/access/nbtree/nbtutils.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtutils.c,v 1.79 2006/10/04 00:29:49 momjian Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtutils.c,v 1.80 2006/12/28 23:16:39 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -24,8 +24,12 @@
#include "miscadmin.h"
#include "storage/lwlock.h"
#include "storage/shmem.h"
#include "utils/lsyscache.h"
static bool _bt_compare_scankey_args(IndexScanDesc scan, ScanKey op,
ScanKey leftarg, ScanKey rightarg,
bool *result);
static void _bt_mark_scankey_required(ScanKey skey);
static bool _bt_check_rowcompare(ScanKey skey,
IndexTuple tuple, TupleDesc tupdesc,
@ -145,7 +149,7 @@ _bt_freestack(BTStack stack)
}
/*----------
/*
* _bt_preprocess_keys() -- Preprocess scan keys
*
* The caller-supplied search-type keys (in scan->keyData[]) are copied to
@ -155,9 +159,9 @@ _bt_freestack(BTStack stack)
*
* The primary purpose of this routine is to discover how many scan keys
* must be satisfied to continue the scan. It also attempts to eliminate
* redundant keys and detect contradictory keys. At present, redundant and
* contradictory keys can only be detected for same-data-type comparisons,
* but that's the usual case so it seems worth doing.
* redundant keys and detect contradictory keys. (If the index opfamily
* provides incomplete sets of cross-type operators, we may fail to detect
* redundant or contradictory keys, but we can survive that.)
*
* The output keys must be sorted by index attribute. Presently we expect
* (but verify) that the input keys are already so sorted --- this is done
@ -184,25 +188,23 @@ _bt_freestack(BTStack stack)
* If possible, redundant keys are eliminated: we keep only the tightest
* >/>= bound and the tightest </<= bound, and if there's an = key then
* that's the only one returned. (So, we return either a single = key,
* or one or two boundary-condition keys for each attr.) However, we can
* only detect redundant keys when the right-hand datatypes are all equal
* to the index datatype, because we do not know suitable operators for
* comparing right-hand values of two different datatypes. (In theory
* we could handle comparison of a RHS of the index datatype with a RHS of
* another type, but that seems too much pain for too little gain.) So,
* keys whose operator has a nondefault subtype (ie, its RHS is not of the
* index datatype) are ignored here, except for noting whether they include
* an "=" condition or not. The logic about required keys still works if
* we don't eliminate redundant keys.
* or one or two boundary-condition keys for each attr.) However, if we
* cannot compare two keys for lack of a suitable cross-type operator,
* we cannot eliminate either. If there are two such keys of the same
* operator strategy, the second one is just pushed into the output array
* without further processing here. We may also emit both >/>= or both
* </<= keys if we can't compare them. The logic about required keys still
* works if we don't eliminate redundant keys.
*
* As a byproduct of this work, we can detect contradictory quals such
* as "x = 1 AND x > 2". If we see that, we return so->quals_ok = FALSE,
* as "x = 1 AND x > 2". If we see that, we return so->qual_ok = FALSE,
* indicating the scan need not be run at all since no tuples can match.
* Again though, only keys with RHS datatype equal to the index datatype
* can be checked for contradictions.
* (In this case we do not bother completing the output key array!)
* Again, missing cross-type operators might cause us to fail to prove the
* quals contradictory when they really are, but the scan will work correctly.
*
* Row comparison keys are treated the same as comparisons to nondefault
* datatypes: we just transfer them into the preprocessed array without any
* Row comparison keys are currently also treated without any smarts:
* we just transfer them into the preprocessed array without any
* editorialization. We can treat them the same as an ordinary inequality
* comparison on the row's first index column, for the purposes of the logic
* about required keys.
@ -211,7 +213,6 @@ _bt_freestack(BTStack stack)
* storage is that we are modifying the array based on comparisons of the
* key argument values, which could change on a rescan. Therefore we can't
* overwrite the caller's data structure.
*----------
*/
void
_bt_preprocess_keys(IndexScanDesc scan)
@ -224,8 +225,7 @@ _bt_preprocess_keys(IndexScanDesc scan)
ScanKey outkeys;
ScanKey cur;
ScanKey xform[BTMaxStrategyNumber];
bool hasOtherTypeEqual;
Datum test;
bool test_result;
int i,
j;
AttrNumber attno;
@ -271,15 +271,11 @@ _bt_preprocess_keys(IndexScanDesc scan)
/*
* Initialize for processing of keys for attr 1.
*
* xform[i] points to the currently best scan key of strategy type i+1, if
* any is found with a default operator subtype; it is NULL if we haven't
* yet found such a key for this attr. Scan keys of nondefault subtypes
* are transferred to the output with no processing except for noting if
* they are of "=" type.
* xform[i] points to the currently best scan key of strategy type i+1;
* it is NULL if we haven't yet found such a key for this attr.
*/
attno = 1;
memset(xform, 0, sizeof(xform));
hasOtherTypeEqual = false;
/*
* Loop iterates from 0 to numberOfKeys inclusive; we use the last pass to
@ -317,9 +313,9 @@ _bt_preprocess_keys(IndexScanDesc scan)
elog(ERROR, "btree index keys must be ordered by attribute");
/*
* If = has been specified, no other key will be used. In case of
* key > 2 && key == 1 and so on we have to set qual_ok to false
* before discarding the other keys.
* If = has been specified, all other keys can be eliminated as
* redundant. In case of key > 2 && key == 1 we can set qual_ok
* to false and abandon further processing.
*/
if (xform[BTEqualStrategyNumber - 1])
{
@ -331,59 +327,56 @@ _bt_preprocess_keys(IndexScanDesc scan)
if (!chk || j == (BTEqualStrategyNumber - 1))
continue;
test = FunctionCall2(&chk->sk_func,
eq->sk_argument,
chk->sk_argument);
if (!DatumGetBool(test))
if (_bt_compare_scankey_args(scan, chk, eq, chk,
&test_result))
{
so->qual_ok = false;
break;
if (!test_result)
{
/* keys proven mutually contradictory */
so->qual_ok = false;
return;
}
/* else discard the redundant non-equality key */
xform[j] = NULL;
}
/* else, cannot determine redundancy, keep both keys */
}
xform[BTLessStrategyNumber - 1] = NULL;
xform[BTLessEqualStrategyNumber - 1] = NULL;
xform[BTGreaterEqualStrategyNumber - 1] = NULL;
xform[BTGreaterStrategyNumber - 1] = NULL;
/* track number of attrs for which we have "=" keys */
numberOfEqualCols++;
}
else
{
/* track number of attrs for which we have "=" keys */
if (hasOtherTypeEqual)
numberOfEqualCols++;
}
/* keep only one of <, <= */
/* try to keep only one of <, <= */
if (xform[BTLessStrategyNumber - 1]
&& xform[BTLessEqualStrategyNumber - 1])
{
ScanKey lt = xform[BTLessStrategyNumber - 1];
ScanKey le = xform[BTLessEqualStrategyNumber - 1];
test = FunctionCall2(&le->sk_func,
lt->sk_argument,
le->sk_argument);
if (DatumGetBool(test))
xform[BTLessEqualStrategyNumber - 1] = NULL;
else
xform[BTLessStrategyNumber - 1] = NULL;
if (_bt_compare_scankey_args(scan, le, lt, le,
&test_result))
{
if (test_result)
xform[BTLessEqualStrategyNumber - 1] = NULL;
else
xform[BTLessStrategyNumber - 1] = NULL;
}
}
/* keep only one of >, >= */
/* try to keep only one of >, >= */
if (xform[BTGreaterStrategyNumber - 1]
&& xform[BTGreaterEqualStrategyNumber - 1])
{
ScanKey gt = xform[BTGreaterStrategyNumber - 1];
ScanKey ge = xform[BTGreaterEqualStrategyNumber - 1];
test = FunctionCall2(&ge->sk_func,
gt->sk_argument,
ge->sk_argument);
if (DatumGetBool(test))
xform[BTGreaterEqualStrategyNumber - 1] = NULL;
else
xform[BTGreaterStrategyNumber - 1] = NULL;
if (_bt_compare_scankey_args(scan, ge, gt, ge,
&test_result))
{
if (test_result)
xform[BTGreaterEqualStrategyNumber - 1] = NULL;
else
xform[BTGreaterStrategyNumber - 1] = NULL;
}
}
/*
@ -412,51 +405,162 @@ _bt_preprocess_keys(IndexScanDesc scan)
/* Re-initialize for new attno */
attno = cur->sk_attno;
memset(xform, 0, sizeof(xform));
hasOtherTypeEqual = false;
}
/* check strategy this key's operator corresponds to */
j = cur->sk_strategy - 1;
/* if row comparison or wrong RHS data type, punt */
if ((cur->sk_flags & SK_ROW_HEADER) || cur->sk_subtype != InvalidOid)
/* if row comparison, push it directly to the output array */
if (cur->sk_flags & SK_ROW_HEADER)
{
ScanKey outkey = &outkeys[new_numberOfKeys++];
memcpy(outkey, cur, sizeof(ScanKeyData));
if (numberOfEqualCols == attno - 1)
_bt_mark_scankey_required(outkey);
if (j == (BTEqualStrategyNumber - 1))
hasOtherTypeEqual = true;
/*
* We don't support RowCompare using equality; such a qual would
* mess up the numberOfEqualCols tracking.
*/
Assert(j != (BTEqualStrategyNumber - 1));
continue;
}
/* have we seen one of these before? */
if (xform[j])
{
/* yup, keep the more restrictive key */
test = FunctionCall2(&cur->sk_func,
cur->sk_argument,
xform[j]->sk_argument);
if (DatumGetBool(test))
xform[j] = cur;
else if (j == (BTEqualStrategyNumber - 1))
{
/* key == a && key == b, but a != b */
so->qual_ok = false;
return;
}
}
else
if (xform[j] == NULL)
{
/* nope, so remember this scankey */
xform[j] = cur;
}
else
{
/* yup, keep only the more restrictive key */
if (_bt_compare_scankey_args(scan, cur, cur, xform[j],
&test_result))
{
if (test_result)
xform[j] = cur;
else if (j == (BTEqualStrategyNumber - 1))
{
/* key == a && key == b, but a != b */
so->qual_ok = false;
return;
}
/* else old key is more restrictive, keep it */
}
else
{
/*
* We can't determine which key is more restrictive. Keep
* the previous one in xform[j] and push this one directly
* to the output array.
*/
ScanKey outkey = &outkeys[new_numberOfKeys++];
memcpy(outkey, cur, sizeof(ScanKeyData));
if (numberOfEqualCols == attno - 1)
_bt_mark_scankey_required(outkey);
}
}
}
so->numberOfKeys = new_numberOfKeys;
}
/*
* Compare two scankey values using a specified operator. Both values
* must be already known non-NULL.
*
* The test we want to perform is logically "leftarg op rightarg", where
* leftarg and rightarg are the sk_argument values in those ScanKeys, and
* the comparison operator is the one in the op ScanKey. However, in
* cross-data-type situations we may need to look up the correct operator in
* the index's opfamily: it is the one having amopstrategy = op->sk_strategy
* and amoplefttype/amoprighttype equal to the two argument datatypes.
*
* If the opfamily doesn't supply a complete set of cross-type operators we
* may not be able to make the comparison. If we can make the comparison
* we store the operator result in *result and return TRUE. We return FALSE
* if the comparison could not be made.
*
* Note: op always points at the same ScanKey as either leftarg or rightarg.
* Since we don't scribble on the scankeys, this aliasing should cause no
* trouble.
*/
static bool
_bt_compare_scankey_args(IndexScanDesc scan, ScanKey op,
ScanKey leftarg, ScanKey rightarg,
bool *result)
{
Relation rel = scan->indexRelation;
Oid lefttype,
righttype,
optype,
opcintype,
cmp_op;
/*
* The opfamily we need to worry about is identified by the index column.
*/
Assert(leftarg->sk_attno == rightarg->sk_attno);
opcintype = rel->rd_opcintype[leftarg->sk_attno - 1];
/*
* Determine the actual datatypes of the ScanKey arguments. We have to
* support the convention that sk_subtype == InvalidOid means the opclass
* input type; this is a hack to simplify life for ScanKeyInit().
*/
lefttype = leftarg->sk_subtype;
if (lefttype == InvalidOid)
lefttype = opcintype;
righttype = rightarg->sk_subtype;
if (righttype == InvalidOid)
righttype = opcintype;
optype = op->sk_subtype;
if (optype == InvalidOid)
optype = opcintype;
/*
* If leftarg and rightarg match the types expected for the "op" scankey,
* we can use its already-looked-up comparison function.
*/
if (lefttype == opcintype && righttype == optype)
{
*result = DatumGetBool(FunctionCall2(&op->sk_func,
leftarg->sk_argument,
rightarg->sk_argument));
return true;
}
/*
* Otherwise, we need to go to the syscache to find the appropriate
* operator. (This cannot result in infinite recursion, since no
* indexscan initiated by syscache lookup will use cross-data-type
* operators.)
*/
cmp_op = get_opfamily_member(rel->rd_opfamily[leftarg->sk_attno - 1],
lefttype,
righttype,
op->sk_strategy);
if (OidIsValid(cmp_op))
{
RegProcedure cmp_proc = get_opcode(cmp_op);
if (RegProcedureIsValid(cmp_proc))
{
*result = DatumGetBool(OidFunctionCall2(cmp_proc,
leftarg->sk_argument,
rightarg->sk_argument));
return true;
}
}
/* Can't make the comparison */
*result = false; /* suppress compiler warnings */
return false;
}
/*
* Mark a scankey as "required to continue the scan".
*