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Support "x IS NOT NULL" clauses as indexscan conditions. This turns out

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to be just a minor extension of the previous patch that made "x IS NULL"
indexable, because we can treat the IS NOT NULL condition as if it were
"x < NULL" or "x > NULL" (depending on the index's NULLS FIRST/LAST option),
just like IS NULL is treated like "x = NULL".  Aside from any possible
usefulness in its own right, this is an important improvement for
index-optimized MAX/MIN aggregates: it is now reliably possible to get
a column's min or max value cheaply, even when there are a lot of nulls
cluttering the interesting end of the index.
This commit is contained in:
Tom Lane
2010-01-01 21:53:49 +00:00
parent 15faca2596
commit 29c4ad9829
18 changed files with 295 additions and 120 deletions
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144
src/backend/access/nbtree/nbtutils.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtutils.c,v 1.94 2009/10/08 22:34:57 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/nbtree/nbtutils.c,v 1.95 2010/01/01 21:53:49 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -276,6 +276,11 @@ _bt_preprocess_keys(IndexScanDesc scan)
* in any particular strategy in this case, so set it to
* BTEqualStrategyNumber --- we can treat IS NULL as an equality
* operator for purposes of search strategy.
*
* Likewise, "x IS NOT NULL" is supported. We treat that as either
* "less than NULL" in a NULLS LAST index, or "greater than NULL"
* in a NULLS FIRST index. However, we have to flip those around in
* a DESC index, to allow for the re-flipping that occurs elsewhere.
*/
if (cur->sk_flags & SK_ISNULL)
{
@ -284,6 +289,21 @@ _bt_preprocess_keys(IndexScanDesc scan)
cur->sk_strategy = BTEqualStrategyNumber;
cur->sk_subtype = InvalidOid;
}
else if (cur->sk_flags & SK_SEARCHNOTNULL)
{
switch (indoption[cur->sk_attno - 1] &
(INDOPTION_DESC | INDOPTION_NULLS_FIRST))
{
case 0: /* ASC / NULLS LAST */
case INDOPTION_DESC | INDOPTION_NULLS_FIRST:
cur->sk_strategy = BTLessStrategyNumber;
break;
default:
cur->sk_strategy = BTGreaterStrategyNumber;
break;
}
cur->sk_subtype = InvalidOid;
}
else
so->qual_ok = false;
}
@ -320,7 +340,7 @@ _bt_preprocess_keys(IndexScanDesc scan)
{
if (i < numberOfKeys)
{
/* See comments above about NULLs and IS NULL handling. */
/* See comments above about NULLs and IS NULL/NOT NULL handling */
/* Note: we assume SK_ISNULL is never set in a row header key */
if (cur->sk_flags & SK_ISNULL)
{
@ -329,6 +349,21 @@ _bt_preprocess_keys(IndexScanDesc scan)
cur->sk_strategy = BTEqualStrategyNumber;
cur->sk_subtype = InvalidOid;
}
else if (cur->sk_flags & SK_SEARCHNOTNULL)
{
switch (indoption[cur->sk_attno - 1] &
(INDOPTION_DESC | INDOPTION_NULLS_FIRST))
{
case 0: /* ASC / NULLS LAST */
case INDOPTION_DESC | INDOPTION_NULLS_FIRST:
cur->sk_strategy = BTLessStrategyNumber;
break;
default:
cur->sk_strategy = BTGreaterStrategyNumber;
break;
}
cur->sk_subtype = InvalidOid;
}
else
{
so->qual_ok = false;
@ -365,13 +400,6 @@ _bt_preprocess_keys(IndexScanDesc scan)
if (!chk || j == (BTEqualStrategyNumber - 1))
continue;
/* IS NULL together with any other predicate must fail */
if (eq->sk_flags & SK_SEARCHNULL)
{
so->qual_ok = false;
return;
}
if (_bt_compare_scankey_args(scan, chk, eq, chk,
&test_result))
{
@ -484,23 +512,6 @@ _bt_preprocess_keys(IndexScanDesc scan)
else
{
/* yup, keep only the more restrictive key */
/* if either arg is NULL, don't try to compare */
if ((cur->sk_flags | xform[j]->sk_flags) & SK_ISNULL)
{
/* at least one of them must be an IS NULL clause */
Assert(j == (BTEqualStrategyNumber - 1));
Assert((cur->sk_flags | xform[j]->sk_flags) & SK_SEARCHNULL);
/* if one is and one isn't, the search must fail */
if ((cur->sk_flags ^ xform[j]->sk_flags) & SK_SEARCHNULL)
{
so->qual_ok = false;
return;
}
/* we have duplicate IS NULL clauses, ignore the newer one */
continue;
}
if (_bt_compare_scankey_args(scan, cur, cur, xform[j],
&test_result))
{
@ -534,8 +545,7 @@ _bt_preprocess_keys(IndexScanDesc scan)
}
/*
* Compare two scankey values using a specified operator. Both values
* must be already known non-NULL.
* Compare two scankey values using a specified operator.
*
* The test we want to perform is logically "leftarg op rightarg", where
* leftarg and rightarg are the sk_argument values in those ScanKeys, and
@ -555,8 +565,7 @@ _bt_preprocess_keys(IndexScanDesc scan)
*
* Note: this routine needs to be insensitive to any DESC option applied
* to the index column. For example, "x < 4" is a tighter constraint than
* "x < 5" regardless of which way the index is sorted. We don't worry about
* NULLS FIRST/LAST either, since the given values are never nulls.
* "x < 5" regardless of which way the index is sorted.
*/
static bool
_bt_compare_scankey_args(IndexScanDesc scan, ScanKey op,
@ -571,6 +580,64 @@ _bt_compare_scankey_args(IndexScanDesc scan, ScanKey op,
cmp_op;
StrategyNumber strat;
/*
* First, deal with cases where one or both args are NULL. This should
* only happen when the scankeys represent IS NULL/NOT NULL conditions.
*/
if ((leftarg->sk_flags | rightarg->sk_flags) & SK_ISNULL)
{
bool leftnull,
rightnull;
if (leftarg->sk_flags & SK_ISNULL)
{
Assert(leftarg->sk_flags & (SK_SEARCHNULL | SK_SEARCHNOTNULL));
leftnull = true;
}
else
leftnull = false;
if (rightarg->sk_flags & SK_ISNULL)
{
Assert(rightarg->sk_flags & (SK_SEARCHNULL | SK_SEARCHNOTNULL));
rightnull = true;
}
else
rightnull = false;
/*
* We treat NULL as either greater than or less than all other values.
* Since true > false, the tests below work correctly for NULLS LAST
* logic. If the index is NULLS FIRST, we need to flip the strategy.
*/
strat = op->sk_strategy;
if (op->sk_flags & SK_BT_NULLS_FIRST)
strat = BTCommuteStrategyNumber(strat);
switch (strat)
{
case BTLessStrategyNumber:
*result = (leftnull < rightnull);
break;
case BTLessEqualStrategyNumber:
*result = (leftnull <= rightnull);
break;
case BTEqualStrategyNumber:
*result = (leftnull == rightnull);
break;
case BTGreaterEqualStrategyNumber:
*result = (leftnull >= rightnull);
break;
case BTGreaterStrategyNumber:
*result = (leftnull > rightnull);
break;
default:
elog(ERROR, "unrecognized StrategyNumber: %d", (int) strat);
*result = false; /* keep compiler quiet */
break;
}
return true;
}
/*
* The opfamily we need to worry about is identified by the index column.
*/
@ -844,11 +911,18 @@ _bt_checkkeys(IndexScanDesc scan,
if (key->sk_flags & SK_ISNULL)
{
/* Handle IS NULL tests */
Assert(key->sk_flags & SK_SEARCHNULL);
if (isNull)
continue; /* tuple satisfies this qual */
/* Handle IS NULL/NOT NULL tests */
if (key->sk_flags & SK_SEARCHNULL)
{
if (isNull)
continue; /* tuple satisfies this qual */
}
else
{
Assert(key->sk_flags & SK_SEARCHNOTNULL);
if (!isNull)
continue; /* tuple satisfies this qual */
}
/*
* Tuple fails this qual. If it's a required qual for the current