pitrou commented on code in PR #40484:
URL: https://github.com/apache/arrow/pull/40484#discussion_r1544470906
##########
cpp/src/arrow/compute/key_hash.cc:
##########
@@ -378,20 +378,40 @@ void Hashing32::HashFixed(int64_t hardware_flags, bool
combine_hashes, uint32_t
}
}
-void Hashing32::HashMultiColumn(const std::vector<KeyColumnArray>& cols,
- LightContext* ctx, uint32_t* hashes) {
- uint32_t num_rows = static_cast<uint32_t>(cols[0].length());
-
- constexpr uint32_t max_batch_size = util::MiniBatch::kMiniBatchLength;
+Status Hashing32::HashMultiColumn(const std::vector<KeyColumnArray>& cols,
+ LightContext* ctx, uint32_t* hashes) {
+ auto num_rows = static_cast<uint32_t>(cols[0].length());
+ // The max_batch_size represents the number of rows to be processed in each
iteration,
+ // and it is used to allocate enough space for the allocated TempVectorStack.
+ const auto max_batch_size =
+ std::min(num_rows,
static_cast<uint32_t>(util::MiniBatch::kMiniBatchLength));
+
+ // pre calculate alloc size in TempVectorStack for hash_temp_buf,
null_hash_temp_buf
+ // and null_indices_buf
+ const auto alloc_hash_temp_buf =
+ util::TempVectorStack::EstimateAllocationSize(max_batch_size *
sizeof(uint32_t));
+ const auto alloc_for_null_indices_buf =
+ util::TempVectorStack::EstimateAllocationSize(max_batch_size *
sizeof(uint16_t));
+ const auto alloc_size = alloc_hash_temp_buf * 2 + alloc_for_null_indices_buf;
+
+ std::unique_ptr<util::TempVectorStack> temp_stack(nullptr);
+ auto stack = ctx->stack;
+ if (!stack) {
Review Comment:
> So for this pr:
> We should mark the key_hash.h --> key_hash_internal.h and add them into
internal namespace?
Yes, +1 to this. We should make the same change for other similar
functionality IMHO (`key_map.h`, `light_array.h`).
> For the enhancement:
> Do you think we should provide users with a hash value that can generate
recordbatch-level?
We can. The API will just have to follow the usual Arrow C++ conventions,
and also be high-level enough.
Note there's another PR lying around for a long time, you might or might not
want to build on it: https://github.com/apache/arrow/pull/39836
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