[BugFix] Do not copy null_column data in fnv_hash() and crc32_hash me…

…thod of NullableColumn (#52885)

## Why I'm doing:
The fnv_hash() method of ArrayColumn is slow when there are NULLs in the array.

## What I'm doing:

Change fnv_hash() method of NullableColumn to not copy null_column data.

Fixes #issue

fnv_hash() method of ArrayColumn is very slow when there are NULLs in the array.

SQLs to reproduce the issue

Query 1 is very fast (the input arrays do not contain NULLs)
```
with input as (select array_generate(1000000) as arr union all select ARRAY_MAP(x -> CASE WHEN x % 2 = 1 THEN 2 ELSE x END, array_generate(1000000)) as arr) select count(distinct arr) from input;
 ```

Query 2 is very slow (one of the input arrays contains NULLs)
```
with input as (select array_generate(1000000) as arr union all select ARRAY_MAP(x -> CASE WHEN x % 2 = 1 THEN NULL ELSE x END, array_generate(1000000)) as arr) select count(distinct arr) from input;
```

The original implementation copies the null_column data in fnv_hash() of NullableColumn and fnv_hash() is called per element in the array.

Benchmark
1. Original Implementation: Query 1 (0.63 s), Query 2 (32.93 s).
2. New Implementation: Query 1 (0.67 s), Query 2 (0.60 s).

Signed-off-by: Yaqi Zhang <[email protected]>
(cherry picked from commit cedf586)

be/src/column/nullable_column.cpp

@@ -312,7 +312,7 @@ void NullableColumn::fnv_hash(uint32_t* hash, uint32_t from, uint32_t to) const
         return;
     }
 
-    auto null_data = _null_column->get_data();
+    const auto& null_data = _null_column->get_data();
     uint32_t value = 0x9e3779b9;
     while (from < to) {
         uint32_t new_from = from + 1;
@@ -337,7 +337,7 @@ void NullableColumn::crc32_hash(uint32_t* hash, uint32_t from, uint32_t to) cons
         return;
     }
 
-    auto null_data = _null_column->get_data();
+    const auto& null_data = _null_column->get_data();
     // NULL is treat as 0 when crc32 hash for data loading
     static const int INT_VALUE = 0;
     while (from < to) {