getKeysResults is typically initialized with 2kb of zeros (16 * 256), which isn't strictly necessary since the only thing we have to initialize is some of the metadata fields. The rest of the data can remain junk as long as we don't access it. This was a bit of a regression in 7.0 with the keyspecs, since we doubled the size of the zeros, but hopefully this recovers a lot of the performance drop.

I saw a modest performance bump for a single shard cluster:

Before:

./src/valkey-benchmark --threads 2 -n 20000000 -r 100000 -d 128 -P 25 -t set
Summary:
  throughput summary: 518672.19 requests per second
  latency summary (msec):
          avg       min       p50       p95       p99       max
        2.328     0.312     2.495     3.231     3.519    11.831

After:

./src/valkey-benchmark --threads 2 -n 20000000 -r 100000 -d 128 -P 25 -t set
Summary:
  throughput summary: 551040.12 requests per second
  latency summary (msec):
          avg       min       p50       p95       p99       max
        2.191     0.840     2.367     2.999     3.207     6.503

I think we would see some comparable improvements in the other places where we are using it such as tracking and ACLs.