[tarantool-patches] Re: [PATCH 3/3] sql: fix passing FP values to integer iterator
Vladislav Shpilevoy
v.shpilevoy at tarantool.org
Thu Jun 6 22:07:12 MSK 2019
Thanks for the fixes!
>>>>> diff --git a/src/box/sql/wherecode.c b/src/box/sql/wherecode.c
>>>>> index 977c0fced..e779729c7 100644
>>>>> --- a/src/box/sql/wherecode.c
>>>>> +++ b/src/box/sql/wherecode.c
>>>>> @@ -1086,31 +1086,61 @@ sqlWhereCodeOneLoopStart(WhereInfo * pWInfo, /* Complete information about the W
>>>>> start_constraints = 1;
>>>>> }
>>>>> struct index_def *idx_pk = space->index[0]->def;
>>>>> - int fieldno = idx_pk->key_def->parts[0].fieldno;
>>>>> -
>>>>> uint32_t pk_part_count = idx_pk->key_def->part_count;
>>>>> - if (pk_part_count == 1 &&
>>>>> - space->def->fields[fieldno].type == FIELD_TYPE_INTEGER) {
>>>>> - /* Right now INTEGER PRIMARY KEY is the only option to
>>>>> - * get Tarantool's INTEGER column type. Need special handling
>>>>> - * here: try to loosely convert FLOAT to INT. If RHS type
>>>>> - * is not INT or FLOAT - skip this ites, i.e. goto addrNxt.
>>>>> - */
>>>>> - int limit = pRangeStart == NULL ? nEq : nEq + 1;
>>>>> - for (int i = 0; i < limit; i++) {
>>>>> - if (idx_def->key_def->parts[i].fieldno ==
>>>>> - idx_pk->key_def->parts[0].fieldno) {
>>>>> - /* Here: we know for sure that table has INTEGER
>>>>> - PRIMARY KEY, single column, and Index we're
>>>>> - trying to use for scan contains this column. */
>>>>> - if (i < nEq)
>>>>> - sqlVdbeAddOp2(v, OP_MustBeInt, regBase + i, addrNxt);
>>>>> - else
>>>>> - force_integer_reg = regBase + i;
>>>>> - break;
>>>>> - }
>>>>> + /*
>>>>> + * Tarantool's iterator over integer fields doesn't
>>>>> + * tolerate floating point values. Hence, if term
>>>>> + * is equality comparison and value of operand is
>>>>> + * not integer, we can skip it since it always
>>>>> + * results in false: INT a == 0.5 -> false;
>>>>> + * It is done using OP_MustBeInt facilities.
>>>>> + * In case term is greater comparison (a > ?), we
>>>>> + * should notify OP_SeekGT to process truncation of
>>>>> + * floating point value: a > 0.5 -> a >= 1;
>>>>> + * It is done by setting P5 flag for OP_Seek*.
>>>>> + * It is worth mentioning that we do not need
>>>>> + * this step when it comes for less comparison:
>>>>> + * key is NULL in this case: values are ordered
>>>>> + * as NULL, ... NULL, min_value, ..., so to
>>>>> + * fetch min value we pass NULL to GT iterator.
>>>>
>>>> 4. I did not get the 'less comparator == compare with NULL'
>>>> idea. Firstly you describe how to compare 'a > ?', this is
>>>> fully understandable. Then you, as I see, go to the 'a < ?'
>>>> case, but somewhy say, that it is the same as 'NULL < ?'.
>>>> Do not understand.
>>>
>>> I say that in this case key which is passed to iterator is NULL
>>> and type of iterator is GE.
>>
>> 2. Why? I still do not understand. What if I wrote 'a < 100'? you
>> do not replace 100 with NULL. But the comment says, that for any
>> 'less' operator a key is NULL: "when it comes for less comparison
>> key is NULL”.
>
> Consider example:
>
> box.execute("CREATE TABLE t1(id INT PRIMARY KEY, a INT UNIQUE);")
> box.execute("INSERT INTO t1 VALUES (1, 1), (2, 2), (3, -1), (4, NULL), (5, NULL);”)
> box.execute("SELECT a FROM t1 WHERE a < 100;”)
>
> Bytecode for this query is:
>
> 102> 0 Init 0 1 0 00 Start at 1
> 102> 1 IteratorOpen 1 1 0 space<name=T1> 00 index id = 1, space ptr = space<name=T1> or reg[0]; unique_unnamed_T1_2
> 102> 2 Explain 0 0 0 SEARCH TABLE T1 USING COVERING INDEX unique_unnamed_T1_2 (A<?) 00
> 102> 3 Null 0 1 0 00 r[1]=NULL
> 102> 4 SeekGT 1 10 1 1 00 key=r[1]
> 102> 5 Integer 100 1 0 00 r[1]=100
> 102> 6 IdxGE 1 10 1 1 00 key=r[1]
> 102> 7 Column 1 1 2 00 r[2]=T1.A
> 102> 8 ResultRow 2 1 0 00 output=r[2]
> 102> 9 Next 1 6 0 00
> 102> 10 Halt 0 0 0 00
>
> As you can see, SeekGT accepts NULL as a key for iterator.
> Then we iterate until search condition is true. So, basically
> 100 is replaced with NULL and not used as a key of iterator.
> I wanted to underline this fact in my comment.
Ah, thanks, now I got it.
Kirill, the patchset LGTM.
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