Implement short circuit function evaluation

[Avogar]

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Changelog category (leave one):

• New Feature

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Implementation of short circuit function evaluation, closes #12587.
Add settings short_circuit_function_evaluation to configure short circuit function evaluation.

Detailed description / Documentation draft:

Short circuit function evaluation

Now for functions if, multiIf, and, or values of their arguments (except the first one) are executed only if they are needed in the result.

1) if(cond, expr_1, expr_2)

expr_1 will be evaluated only on rows where cond is true, expr_2 - where condition is false.

Example:

SELECT if(number = 0, 0, intDiv(42, number)) FROM numbers(10)

In this example we won't get an exception about division by zero because intDiv(42, number) will be evaluated only for numbers that doesn't satisfy condition number = 0.

2) multiIf(cond_1, expr_1, cond_2, expr_2, ..., cond_{n-1}, expr_{n-1}, )

expr_i will be evaluated only on rows where (not cond_1) and (NOT cond_2) and ... and (not cond_{i-1}) and cond_i is true.
cond_i will be evaluated only on rows where (not cond_1) and (not cond_2) and ... and (not cond_{i-1}) is true.

Example:

SELECT multiIf(number == 0, 0, number == 1, intDiv(1, number), number == 2, intDiv(1, number - 1), number == 3, intDiv(1, number - 2), intDiv(1, number - 3)) FROM numbers(10);

In this example we won't get an exception about division by zero.

3) expr_1 and expr_2 and ... and expr_n

expr_i will be evaluated only on rows where expr_1 and expr_2 and ... and expr_{i-1} is true.

Example:

SELECT number != 0 and intDiv(1, number) == 0 and number != 2 and intDiv(1, number - 2) == 0 FROM numbers(10);

In this example we won't get an exception about division by zero.

4) expr_1 or expr_2 or ... or exp_n

expr_i will be evaluated only on rows where (not expr_1) and (not expr_2) and ... and (not expr_{i-1}) is true.

Example:

SELECT number == 0 or intDiv(1, number) != 0 or number == 2 or intDiv(1, number - 2) != 0 FROM numbers(10);

In this example we won't get an exception about division by zero.

User setting

There is a new setting for users: short_circuit_function_evaluation. Possible values:

• enable Enables short-circuit function evaluation for functions that are suitable for it (can throw or computationally heavy).
• force_enable Enables short-circuit function evaluation for all functions.
• disable Disables short-circuit function evaluation.

[KochetovNicolai]

I suppose arrayJoin also should be supported.
E.g.: select if(number != 0, arrayJoin([1, intDiv(42, number), 2]), 0)
Here, arrayJoin for short-circuit column will work as if array is empty for mask = 0.

[Avogar]

I suppose arrayJoin also should be supported

I spent a lot of time thinking about how to support it for arrayJoin, but I considered that it's almost impossible. I wrote a comment about it:
https://github.com/ClickHouse/ClickHouse/blob/591cecc66499e99948001a82b0f03e1ced4c7763/src/Interpreters/ExpressionActions.cpp#L81-L87

[KochetovNicolai]

But I think it is ok to get offsets after filtering.
select if (number % 2 = 0, [], arrayJoin(range(number))) from numbers(4);
Ordinary evaluation
[0, 1, 2, 3] -> range -> [[], [0], [0, 1], [0, 1, 2]] -> arrayJoin -> [0, 0, 1, 0, 1, 2] -> if -> [0, 0, 1, 2]
[1, 0, 1, 0] -> arrayJoin -> [0, 1, 1, 0, 0, 0]

short-circuit evaluation
if -> [?, 1, ?, 3] -> range -> [?, [0], ?, [0, 1, 2]] -> arrayJoin -> [0, 0, 1, 2]
if -> [1, 0, 1, 0]

But we can support it later (if needed)

[Avogar]

@Mergifyio update

[mergify]

Command update: success

Branch has been successfully updated

[KochetovNicolai]

:) select if(number > 0, intDiv(42, number), 0) from numbers(4)

SELECT if(number > 0, intDiv(42, number), 0)
FROM numbers(4)

Query id: 9d6e83c0-b3e9-4a71-b03a-d03307aafe8d

┌─if(greater(number, 0), intDiv(42, number), 0)─┐
│                                             0 │
│                                            42 │
│                                            21 │
│                                            14 │
└───────────────────────────────────────────────┘

4 rows in set. Elapsed: 0.003 sec. 

 :) select if(number = 0, 0, intDiv(42, number)) from numbers(4)

SELECT if(number = 0, 0, intDiv(42, number))
FROM numbers(4)

Query id: 27a0f2c2-a395-4346-a332-2a41b666072d

┌─if(equals(number, 0), 0, intDiv(42, number))─┐
│                                            0 │
│                                           42 │
│                                           21 │
│                                           14 │
└──────────────────────────────────────────────┘

4 rows in set. Elapsed: 0.002 sec. 


 :) select if(number > 0, intDiv(42, number), 0), if(number = 0, 0, intDiv(42, number)) from numbers(4)

SELECT
    if(number > 0, intDiv(42, number), 0),
    if(number = 0, 0, intDiv(42, number))
FROM numbers(4)

Query id: 2219d4ed-5dcc-4906-9b37-0b0c6093802f


0 rows in set. Elapsed: 0.004 sec. 

Received exception from server (version 21.7.1):
Code: 153. DB::Exception: Received from localhost:9000. DB::Exception: Division by zero: while executing 'FUNCTION intDiv(42 :: 2, number :: 0) -> intDiv(42, number) UInt8 : 5'. 

[KochetovNicolai]

:) select if(if(number > 0, intDiv(42, number), 7), intDiv(42, number), 8) from numbers(4) format TSV

SELECT if(if(number > 0, intDiv(42, number), 7), intDiv(42, number), 8)
FROM numbers(4)
FORMAT TSV

Query id: d55177ae-ccb0-4ba9-9194-66781b257493


0 rows in set. Elapsed: 0.004 sec. 

Received exception from server (version 21.7.1):
Code: 153. DB::Exception: Received from localhost:9000. DB::Exception: Division by zero: while executing 'FUNCTION intDiv(42 :: 2, number :: 0) -> intDiv(42, number) UInt8 : 1'. 

:) select if(number > 0, intDiv(42, number), 7) from numbers(4) format TSV

SELECT if(number > 0, intDiv(42, number), 7)
FROM numbers(4)
FORMAT TSV

Query id: 0d7e3fb5-7f18-4297-a1e1-01e66dfbdc3a

7
42
21
14

4 rows in set. Elapsed: 0.003 sec. 

:) select if(number > 0, intDiv(42, number), 8) from numbers(4) format TSV

SELECT if(number > 0, intDiv(42, number), 8)
FROM numbers(4)
FORMAT TSV

Query id: bae9fdd8-97b5-4d9a-b31b-429b0936f04d

8
42
21
14

4 rows in set. Elapsed: 0.003 sec. 

[KochetovNicolai]

I checked everything except MaskOperations.cpp and IColumn::expand implementation for different columns (btw, do we still need it?). What I have checked looks almost perfect. I think it is 99% ready to be merged.

I see that some binary .arrow and .parquet files are added here. Was it by mistake? Looks like we need to remove them.

[KochetovNicolai]

Maybe exception from the main loop may prevent vectorisation ...
But I am ok with such implementation for now

[KochetovNicolai]

LGTM to merge it

[KochetovNicolai]

But also let's wait for perftest.

[Avogar]

@Mergifyio update

[mergify]

Command update: success

Branch has been successfully updated

[sevirov]

Internal documentation ticket: DOCSUP-13429

[azat]

I found it interesting that even with short circuit evaluation disabled, there is still huge overhead:

SELECT count() FROM zeros(1000000000) WHERE NOT ignore(if(rand() % 2, toDateTime(rand()), toDate(rand()))) settings max_threads=1, short_circuit_function_evaluation='disable'
-- 11.8sec

SELECT count() FROM zeros(1000000000) WHERE NOT ignore(if(rand() % 2, toDateTime(rand()), toDate(rand()))) settings max_threads=1
-- 11.88sec

SELECT count() FROM zeros(1000000000) WHERE NOT ignore(if(rand() % 2, toDateTime(rand()), toDate(rand()))) settings max_threads=1
-- 8.2sec on 21.7 w/o https://github.com/ClickHouse/ClickHouse/pull/23367