Reduce overhead in command propagation

[tezc]

Refactor command propagation code to reduce overhead on master

Currently, the main bottleneck is feedReplicationBuffer(). It is called for each argument in the command and has bookkeeping overhead on every call (e.g. checking whether to attach replicas to the replication backlog). It is also not inlined by the compiler. These costs become more visible with pipelining and commands with many arguments (e.g. HSET with many fields).

Changes:

• Defer all bookkeeping to be done once per command instead of once per command argument.
• Refactor the hot path so the compiler can inline replBufWriterAppend().
• Add replBufWritterAppendBulkLen() that uses shared RESP headers for small values, avoiding formatting overhead.

These changes should not introduce any behavioral change.

TODO: In a follow-up PR, explore forwarding the exact command from the client querybuf to avoid re-serialization. Many commands are propagated without modification and can benefit from this.

--

Benchmark	Before (ops/s)	After (ops/s)	Improvement
SET	256,048	265,131	+3%
SET (pipeline)	1,477,310	1,671,272	+13%
HSET 10 fields	145,000	158,000	+9%
HSET 10 fields (pipeline)	363,483	430,855	+18%
HSET 10 fields, 15B values (pipeline)	387,443	487,135	+26%
ZADD 5 members	180,700	193,519	+7%
ZADD 5 members (pipeline)	466,453	564,872	+21%

---

Co-authored-by: Yuan Wang yuan.wang@redis.com

[tezc]

Test Case	Baseline redis/redis unstable (median obs. +- std.dev)	Comparison tezc/redis f541025 (median obs. +- std.dev)	% change (higher-better)	Note
memtier_benchmark-1key-load-hash-1K-fields-with-5B-values	5115	6192	21.1%	IMPROVEMENT
memtier_benchmark-10Kkeys-load-list-rpush-bulkload-pipeline-50	99517 +- 0.0% (2 datapoints)	118988	19.6%	IMPROVEMENT
memtier_benchmark-10Mkeys-load-hash-5-fields-with-10B-values-pipeline-10	494431 +- 0.2% (2 datapoints)	577477	16.8%	IMPROVEMENT
memtier_benchmark-stream-10M-entries-xreadgroup-count-100	7828	9095	16.2%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-50-fields-with-10B-values	45907	52075	13.4%	IMPROVEMENT
memtier_benchmark-stream-concurrent-xadd-xreadgroup-70-30	102797	116363	13.2%	IMPROVEMENT
memtier_benchmark-10Mkeys-load-hash-5-fields-with-100B-values-pipeline-10	375260 +- 0.6% (2 datapoints)	423213	12.8%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-50-fields-with-100B-values	55745 +- 0.3% (2 datapoints)	62352 +- 0.2% (2 datapoints)	11.9%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-10B-values-pipeline-100-nokeyprefix	1725389	1919690	11.3%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-10B-values-pipeline-500	1694296	1874943	10.7%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-20-fields-with-1B-values-pipeline-30	46878 +- 0.1% (2 datapoints)	51574 +- 1.4% (2 datapoints)	10.0%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-10B-values-pipeline-100	1588013	1741303	9.7%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-stream-5-fields-with-100B-values-pipeline-10	286285	313716	9.6%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-stream-1-fields-with-100B-values-pipeline-10	504875	553124	9.6%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-10B-values-pipeline-50	1471440	1609986	9.4%	IMPROVEMENT
memtier_benchmark-stream-concurrent-xadd-xreadgroup-70-30-1k-consumers-claim	93720	101995	8.8%	IMPROVEMENT
memtier_benchmark-1Mkeys-generic-scan-type-pipeline-10	727840	790523	8.6%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-setrange-100B-pipeline-10	933723	1008576	8.0%	IMPROVEMENT
memtier_benchmark-nokeys-pubsub-publish-1K-channels-10B-no-subscribers	1330352	1430084	7.5%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-mset-10-keys-with-100B-values	128662	138133	7.4%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-mset-10-keys-with-10B-values	132748	142487	7.3%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-setex-100B-pipeline-10	767951	821765	7.0%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-incrby-pipeline-10	1100411	1176282	6.9%	IMPROVEMENT
memtier_benchmark-1Kkeys-hash-listpack-500-fields-update-20-fields-with-1B-to-64B-values	74319 +- 0.6% (2 datapoints)	79407	6.8%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-10B-values-pipeline-10	964363	1027089	6.5%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-50-fields-with-10B-values-short-expiration	20333 +- 0.0% (2 datapoints)	21630 +- 0.6% (2 datapoints)	6.4%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-set-with-ex-100B-pipeline-10	767663	816392	6.3%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-append-1-100B-pipeline-10	966112	1027139	6.3%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-5-fields-with-10B-values-short-expiration	121723 +- 0.0% (2 datapoints)	129011 +- 0.2% (2 datapoints)	6.0%	IMPROVEMENT
memtier_benchmark-stream-concurrent-xadd-xreadgroup-100-1-1k-consumers-claim-count100	147712	156391	5.9%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-list-with-10B-values-pipeline-10	930133	985198	5.9%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-hash-50-fields-with-10B-values-long-expiration-pipeline-10	23739	25141	5.9%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-5-fields-with-10B-values-expiration	133831 +- 0.5% (2 datapoints)	141785 +- 1.3% (2 datapoints)	5.9%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-incr-pipeline-10	1179925	1248548	5.8%	IMPROVEMENT
memtier_benchmark-stream-concurrent-xadd-xreadgroup-100-1-1k-consumers-count100	153279	162061	5.7%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-100B-values-pipeline-10	952361	1007115	5.7%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-50-fields-with-10B-values-long-expiration	20988 +- 0.6% (2 datapoints)	22108 +- 0.0% (2 datapoints)	5.3%	IMPROVEMENT
memtier_benchmark-10Kkeys-load-list-with-10B-values-pipeline-50	1053115 +- 0.1% (2 datapoints)	1107446	5.2%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-50-fields-with-10B-values-expiration	20937 +- 0.0% (2 datapoints)	22021 +- 0.6% (2 datapoints)	5.2%	IMPROVEMENT
memtier_benchmark-2keys-lua-evalsha-hset-expire	128490	134607	4.8%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-incrbyfloat-pipeline-10	612220	640979	4.7%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-50-fields-with-1000B-values	16132 +- 2.0% (2 datapoints)	16887 +- 0.9% (2 datapoints)	4.7%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hexpireat-5-fields-10B-values	152985 +- 0.6% (2 datapoints)	160161 +- 0.7% (2 datapoints)	4.7%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-incrby	213780	223444	4.5%	IMPROVEMENT
memtier_benchmark-10Mkeys-load-hash-5-fields-with-10B-values	156019 +- 0.4% (2 datapoints)	163047	4.5%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hpexpire-5-fields-10B-values	153962 +- 0.3% (2 datapoints)	160804 +- 0.8% (2 datapoints)	4.4%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-set-intset-with-100-elements-19-digits-pipeline-10	61512	64181	4.3%	IMPROVEMENT
memtier_benchmark-1Mkeys-hash-transactions-multi-exec-pipeline-20	1488720	1552096	4.3%	IMPROVEMENT
memtier_benchmark-3Mkeys-load-string-with-512B-values-pipeline-10	726183	756702	4.2%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-string-with-1KiB-values-pipeline-10	588843	613179	4.1%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-stream-5-fields-with-100B-values	128074	133138	4.0%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-5-fields-with-10B-values-long-expiration	135021 +- 1.1% (2 datapoints)	140378 +- 0.6% (2 datapoints)	4.0%	IMPROVEMENT
memtier_benchmark-100Kkeys-load-hash-1-fields-with-10B-values-short-expiration	165317 +- 0.5% (2 datapoints)	171866 +- 0.4% (2 datapoints)	4.0%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hexpireat-50-fields-10B-values	31157 +- 0.0% (2 datapoints)	32366 +- 0.1% (2 datapoints)	3.9%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-mixed-50-50-set-get-100B-expire-pipeline-10	856442	889194	3.8%	IMPROVEMENT
memtier_benchmark-10Mkeys-load-hash-5-fields-with-100B-values	143908 +- 0.4% (2 datapoints)	149362	3.8%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-set-intset-with-100-elements-19-digits	51521	53414	3.7%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hpexpire-50-fields-10B-values	30415 +- 0.0% (2 datapoints)	31551 +- 0.1% (2 datapoints)	3.7%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hexpire-5-fields-10B-values	153719 +- 0.4% (2 datapoints)	159407 +- 0.1% (2 datapoints)	3.7%	IMPROVEMENT
memtier_benchmark-connection-hello	204160	211424	3.6%	IMPROVEMENT
memtier_benchmark-1Mkeys-string-mixed-50-50-set-get-100B-pipeline-10	976426	1011991	3.6%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hpexpireat-50-fields-10B-values	31451 +- 0.1% (2 datapoints)	32569 +- 0.1% (2 datapoints)	3.6%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hgetex-50-fields-10B-values	21412 +- 0.7% (2 datapoints)	22188 +- 0.1% (2 datapoints)	3.6%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hexpire-50-fields-10B-values	30424 +- 0.1% (2 datapoints)	31498 +- 0.1% (2 datapoints)	3.5%	IMPROVEMENT
memtier_benchmark-2keys-lua-eval-hset-expire	114908	118813	3.4%	IMPROVEMENT
memtier_benchmark-1Mkeys-hash-hget-hgetall-hkeys-hvals-with-100B-values	219567	226991	3.4%	IMPROVEMENT
memtier_benchmark-stream-concurrent-xadd-xreadgroup-70-30-1k-consumers	150389	155318	3.3%	IMPROVEMENT
memtier_benchmark-100Kkeys-hash-hpexpireat-5-fields-10B-values	157828 +- 0.8% (2 datapoints)	163114 +- 0.4% (2 datapoints)	3.3%	IMPROVEMENT
memtier_benchmark-1Mkeys-load-zset-listpack-with-100-elements-double-score	6105 +- 0.0% (2 datapoints)	6304	3.2%	IMPROVEMENT
memtier_benchmark-1Mkeys-generic-scan-cursor-count-500-pipeline-10	10849	11200	3.2%	IMPROVEMENT

[ShooterIT]

this idea looks good to me, some small comments

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Reviewed by Cursor Bugbot for commit 4eeadae. Configure here.}