Preallocate HvAUX() structures for large bucket arrays

The assumption is that the time/space tradeoff of not allocating
the HvAUX() structure goes away for a large bucket array where the
size of the allocated buffer is much larger than the nonallocated
HvAUX() "extension".

This should make keys() and each() on larger hashes faster, but
still preserve the essence of the original space conservation,
where the assumption is a lot of small hash based objects which
will never be traversed.

1 files changed, 10 insertions, 0 deletions

diff --git a/hv.h b/hv.h
index 5b52f98460..8ff1d140f3 100644
--- a/hv.h
+++ b/hv.h
@@ -238,6 +238,16 @@ C<SV*>.
 */
 
 #define PERL_HASH_DEFAULT_HvMAX 7
+/* HvMAX(hv)+1 is >= to this we preallocate the HvAUX() struct during hsplit()
+ * The assumption being that we are using so much space anyway we might
+ * as well allocate the extra bytes and speed up later keys()
+ * or each() operations. We don't do this to small hashes as we assume
+ * that a) it will be easy/fast to resize them to add the iterator, and b) that
+ * many of them will be objects which won't be traversed. Larger hashes however
+ * will take longer to extend, and the size of the aux struct is swamped by the
+ * overall length of the bucket array.
+ * */
+#define PERL_HV_ALLOC_AUX_SIZE (1 << 9)
 
 /* these hash entry flags ride on hent_klen (for use only in magic/tied HVs) */
 #define HEf_SVKEY	-2	/* hent_key is an SV* */