ClickHouse ： arrayMap, arrayJoin or ARRAY JOIN memory usage

Why arrayMap, arrayFilter, arrayJoin use so much memory?

arrayMap-like functions memory usage calculation.

In order to calculate arrayMap or similar array* functions ClickHouse temporarily does arrayJoin-like operation, which in certain conditions can lead to huge memory usage for big arrays.

So for example, you have 2 columns:

SELECT *
FROM
(
    SELECT
        [1, 2, 3, 4, 5] AS array_1,
        [1, 2, 3, 4, 5] AS array_2
)

┌─array_1─────┬─array_2─────┐
│ [1,2,3,4,5] │ [1,2,3,4,5] │
└─────────────┴─────────────┘

Let’s say we want to multiply array elemen