westonpace commented on code in PR #41335:
URL: https://github.com/apache/arrow/pull/41335#discussion_r1598538825
##########
cpp/src/arrow/compute/key_hash_internal.h:
##########
@@ -161,6 +167,12 @@ class ARROW_EXPORT Hashing64 {
static void HashMultiColumn(const std::vector<KeyColumnArray>& cols,
LightContext* ctx,
uint64_t* hashes);
+ // Clarify the max temp stack usage for HashBatch so the caller could
reserve enough
+ // size in advance.
+ static constexpr auto kHashBatchTempStackUsage =
+ (sizeof(uint16_t) + sizeof(uint64_t) + /*extra=*/1) *
Review Comment:
Minor nit: but why does this constant have 2 `sizeof` calls in the
calculation but the previous constant has 3 `sizeof` calls?
##########
cpp/src/arrow/compute/row/compare_internal.h:
##########
@@ -32,6 +32,13 @@ namespace compute {
class ARROW_EXPORT KeyCompare {
public:
+ // Clarify the max temp stack usage for CompareColumnsToRows so the caller
could reserve
+ // enough size in advance.
+ constexpr static int64_t CompareColumnsToRowsTempStackUsage(int64_t
num_rows) {
+ return (sizeof(uint8_t) + sizeof(uint8_t) + sizeof(uint8_t)) * num_rows +
Review Comment:
Maybe add comments in these blocks explaining what each of the parts is?
Also, elsewhere we multiple by `kMiniBatchLength` but here it seems we are
adding `kMiniBatchLength`. Why the difference?
##########
cpp/src/arrow/compute/key_hash_internal.h:
##########
@@ -48,6 +48,12 @@ class ARROW_EXPORT Hashing32 {
static void HashMultiColumn(const std::vector<KeyColumnArray>& cols,
LightContext* ctx,
uint32_t* out_hash);
+ // Clarify the max temp stack usage for HashBatch so the caller could
reserve enough
+ // size in advance.
Review Comment:
I'm not sure I understand this comment.
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