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perf: Avoid per-key heap allocation in ra_find_node hash path

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When a RedisArray uses a custom hash algorithm, ra_find_node allocated
the hash context and digest buffers on the heap for every key lookup.
Both are small (the largest common context is SHA-512 at ~208 bytes),
so use stack buffers for the common case and fall back to emalloc only
when an algorithm's context or digest exceeds them.

The context buffer is a union with a double member to guarantee the
alignment the context structs require for their uint64_t state.
This commit is contained in:
Ilia Alshanetsky
2026-06-02 18:11:30 -04:00
committed by Michael Grunder
parent da514c71bb
commit 8b746bfc78
1 changed files with 11 additions and 4 deletions
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redis_array_impl.c
+11 -4
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@@ -497,8 +497,15 @@ ra_find_node(RedisArray *ra, const char *key, int key_len, int *out_pos)
/* hash */
if (ra->algorithm && (ops = redis_hash_fetch_ops(ra->algorithm))) {
void *ctx = emalloc(ops->context_size);
unsigned char *digest = emalloc(ops->digest_size);
/* The union forces alignment suitable for any hash context
* struct (they hold uint64_t state); fall back to the heap for
* the rare algorithm whose context/digest exceeds the buffer. */
union { double align; unsigned char buf[256]; } ctx_stack;
unsigned char digest_stack[64];
void *ctx = ops->context_size <= sizeof(ctx_stack) ? (void *)&ctx_stack
: emalloc(ops->context_size);
unsigned char *digest = ops->digest_size <= sizeof(digest_stack) ? digest_stack
: emalloc(ops->digest_size);
#if PHP_VERSION_ID >= 80100
ops->hash_init(ctx,NULL);
@@ -511,8 +518,8 @@ ra_find_node(RedisArray *ra, const char *key, int key_len, int *out_pos)
memcpy(&ret, digest, MIN(sizeof(ret), ops->digest_size));
ret %= 0xffffffff;
efree(digest);
efree(ctx);
if (digest != digest_stack) efree(digest);
if (ctx != (void *)&ctx_stack) efree(ctx);
} else {
for (i = 0; i < ZSTR_LEN(out); ++i) {
CRC32(ret, ZSTR_VAL(out)[i]);