perf: Avoid per-key heap allocation in ra_find_node hash path#2856
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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.
michael-grunder
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Jun 2, 2026
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Good use of this trick.
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When a RedisArray uses a custom hash algorithm,
ra_find_nodeallocated 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).Use stack buffers for the common case and fall back to
emalloconly when an algorithm's context or digest exceeds them. The context buffer is a union with adoublemember to guarantee the alignment the context structs require for theiruint64_tstate.Built on PHP 8.4; runtime-tested with a RedisArray under md5 and sha256, 200 keys round-tripping correctly.