perf: split CommandComplete tags on char (instead of String) by jkaczman · Pull Request #2011 · pgdogdev/pgdog

jkaczman · 2026-11-11T14:23:28Z

Postgres sends CommandComplete messages with the command at the end of all queries (e.g., INSERT 0 5 after an INSERT of 5 rows). Then, we use Stats::rows_affected to look at the tag of these CommandComplete messages (e.g., INSERT in INSERT 0 5) via the method CommandComplete::tag.

Previously, CommandComplete::tag was splitting the message via a 1-character string (" ") to find the tag. Rust's standard library searches for strings with TwoWaySearcher, the general substring search, which does extra work, such as analyzing the string before searching, which costs extra instructions.

Even in release builds with all optimizations on, the compiler doesn't replace the string " " with the char ' '.

This is now fixed to split on the char ' ', which runs about 56 CPU instructions per call instead of about 224

codecov · 2026-11-11T14:26:55Z

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

github-actions · 2026-11-11T15:05:36Z

Metal bench (arm64) passed. All 517 measures within bounds.

suite	throughput	cpu/txn	user cycles/txn	user instr/txn	kernel cycles/txn	kernel instr/txn	ctx/txn
pooler		19.05 (+0.1% ± 1.1%)	18,552 (+0.3% ± 0.8%)	31,925 (-0.4% ± 0.08%)	30,159 (-0.1% ± 2.4%)	51,077 (-0.1% ± 0.5%)
lb		19.66 (+0.4% ± 1.2%)	19,161 (+0.2% ± 0.5%)	32,811 (-0.4% ± 0.07%)	30,838 (+0.7% ± 2.0%)	52,134 (-0.0% ± 0.2%)
sharding-w2		31.38 (+0.0% ± 1.2%)	42,829 (+0.0% ± 1.2%)	97,315 (-0.1% ± 0.02%)	38,515 (-0.2% ± 2.6%)	53,748 (+0.0% ± 0.2%)	1.552 (+0.1% ± 0.2%)
sharding-w8	250,620 (+0.2% ± 3.8%)	28.4 (-0.4% ± 3.9%)	43,424 (-0.4% ± 2.6%)	52,835 (-0.2% ± 0.08%)	34,987 (-0.3% ± 5.6%)	42,408 (-0.0% ± 0.2%)	0.1728 (-0.1% ± 3.0%)

Counters per txn

suite	frontend stall	l1i refill
pooler	7,964 (+1.4% ± 2.2%)	2,650 (+0.3% ± 0.9%)
lb	8,294 (+1.5% ± 1.4%)	2,707 (+0.3% ± 0.6%)
sharding-w2	16,327 (-0.5% ± 2.8%)	3,923 (-0.2% ± 1.8%)
sharding-w8	17,892 (-1.8% ± 4.2%)	3,780 (-1.2% ± 2.3%)

Microbench: all 504 measures within bounds.

Hot code per txn

path	base	head	change
pooler	111.4 KB	111.7 KB	+0.2 KB
sharding-w2	164.6 KB	163.7 KB	-0.9 KB

pooler:

crate	base	head	change
pgdog::frontend::client::query_engine	19.4 KB	19.5 KB	+0.1 KB
tokio	18.4 KB	18.3 KB	-0.1 KB
pgdog::backend::pool	17.4 KB	17.6 KB	+0.2 KB
aws-lc (TLS crypto)	10.7 KB	10.3 KB	-0.4 KB
rustls (TLS)	8.1 KB	8.4 KB	+0.3 KB
pgdog::frontend (other)	7.8 KB	7.8 KB	+0.1 KB
pgdog::backend::server	7.3 KB	7.2 KB	-0.1 KB
other	6.2 KB	6.4 KB	+0.2 KB
everything else	16.1 KB	16.1 KB	-0.1 KB

function	head	change
`pgdog::frontend::client::Client::run::{{closure}}`	5.5 KB	+0.0 KB
`pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:`	5.2 KB	+0.1 KB
`pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}`	4.1 KB	+0.1 KB
`tokio::runtime::task::raw::poll`	3.2 KB	+0.0 KB
`pgdog::backend::server::Server::read::{{closure}}`	2.9 KB	+0.1 KB

sharding-w2:

crate	base	head	change
pgdog::frontend::router	28.6 KB	28.1 KB	-0.5 KB
pgdog::frontend::client::query_engine	20.6 KB	20.5 KB	-0.1 KB
tokio	18.4 KB	18.4 KB	+0.1 KB
pgdog::backend::pool	18.3 KB	17.8 KB	-0.5 KB
aws-lc (TLS crypto)	13.2 KB	13.0 KB	-0.2 KB
other	9.7 KB	9.9 KB	+0.2 KB
pgdog::frontend (other)	8.4 KB	8.6 KB	+0.1 KB
rustls (TLS)	8.1 KB	7.9 KB	-0.2 KB
everything else	39.2 KB	39.4 KB	+0.2 KB

function	head	change
`pgdog::frontend::client::Client::run::{{closure}}`	6.0 KB	+0.0 KB
`pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:`	5.1 KB	+0.1 KB
`pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}`	3.9 KB	-0.2 KB
`pgdog::frontend::router::parser::query::select::<impl pgdog::frontend::router::parser::que`	3.3 KB	-0.1 KB
`tokio::runtime::task::raw::poll`	3.2 KB	+0.1 KB

lb flamegraph vs a2b6aa9

Open interactive for hover, zoom and search.

Open interactive.

microbench flamegraph vs a2b6aa9

Open interactive for hover, zoom and search.

Open interactive.

pooler flamegraph vs a2b6aa9

Open interactive for hover, zoom and search.

Open interactive.

sharding-w2 flamegraph vs a2b6aa9

Open interactive for hover, zoom and search.

Open interactive.

sharding-w8 flamegraph vs a2b6aa9

Open interactive for hover, zoom and search.

Open interactive.

Logs

lb, microbench, pooler, sharding-w2, sharding-w8, verdict.json

Compared b47ea9b with a2b6aa9 on m8g.metal-24xl (spot).

github-actions · 2026-11-11T15:06:13Z

Metal bench (x86) passed. All 517 measures within bounds.

suite	throughput	cpu/txn	user cycles/txn	user instr/txn	kernel cycles/txn	kernel instr/txn	ctx/txn
pooler		34.53 (-0.2% ± 0.2%)	22,555 (-0.4% ± 0.3%)	33,810 (-0.5% ± 0.02%)	57,648 (-0.2% ± 0.3%)	38,540 (+0.1% ± 0.2%)
lb		35.55 (+0.1% ± 0.3%)	23,662 (-0.0% ± 0.9%)	34,758 (-0.2% ± 0.8%)	58,644 (+0.2% ± 0.3%)	39,202 (-0.0% ± 0.2%)
sharding-w2		55.57 (-0.3% ± 0.1%)	51,790 (-0.4% ± 1.0%)	101,191 (-0.2% ± 0.08%)	71,841 (-0.3% ± 1.2%)	43,124 (+0.0% ± 0.4%)	1.398 (+0.1% ± 0.3%)
sharding-w8	149,345 (-0.1% ± 0.6%)	48.02 (+0.0% ± 0.6%)	58,130 (+0.1% ± 1.2%)	56,625 (-0.3% ± 0.02%)	63,734 (-0.0% ± 0.4%)	34,219 (+0.0% ± 0.2%)	0.1697 (+0.1% ± 0.6%)

Counters per txn

suite	frontend stall	l1i refill
pooler	71,308 (-0.5% ± 1.2%)	3,595 (-0.6% ± 0.2%)
lb	73,761 (+0.1% ± 1.0%)	3,716 (-0.5% ± 0.10%)
sharding-w2	146,715 (-0.1% ± 1.2%)	5,850 (-0.7% ± 0.9%)
sharding-w8	119,228 (-0.5% ± 2.9%)	4,825 (-0.4% ± 0.6%)

Microbench: all 504 measures within bounds.

Hot code per txn

path	base	head	change
pooler	101.8 KB	103.4 KB	+1.6 KB
sharding-w2	157.9 KB	157.7 KB	-0.2 KB

pooler:

crate	base	head	change
pgdog::frontend::client::query_engine	19.2 KB	19.9 KB	+0.7 KB
tokio	17.3 KB	17.6 KB	+0.2 KB
pgdog::backend::pool	16.8 KB	17.2 KB	+0.4 KB
pgdog::frontend (other)	8.8 KB	9.1 KB	+0.3 KB
rustls (TLS)	6.9 KB	6.9 KB	+0.1 KB
aws-lc (TLS crypto)	6.9 KB	6.9 KB	+0.0 KB
pgdog::backend::server	6.2 KB	6.4 KB	+0.2 KB
other	5.9 KB	5.6 KB	-0.3 KB
everything else	13.9 KB	13.8 KB	-0.1 KB

function	head	change
`pgdog::frontend::client::Client::run::{{closure}}`	6.9 KB	+0.4 KB
`pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:`	6.0 KB	+0.4 KB
`pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}`	4.6 KB	+0.1 KB
`tokio::runtime::task::raw::poll`	3.6 KB	+0.0 KB
`pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:`	2.8 KB	-0.1 KB

sharding-w2:

crate	base	head	change
pgdog::frontend::router	27.2 KB	26.9 KB	-0.2 KB
pgdog::frontend::client::query_engine	22.1 KB	22.1 KB	+0.1 KB
tokio	17.9 KB	18.2 KB	+0.3 KB
pgdog::backend::pool	17.8 KB	17.9 KB	+0.1 KB
aws-lc (TLS crypto)	10.0 KB	9.9 KB	-0.1 KB
other	9.7 KB	9.9 KB	+0.2 KB
pgdog::frontend (other)	10.2 KB	9.9 KB	-0.3 KB
rustls (TLS)	7.3 KB	7.3 KB	+0.0 KB
everything else	35.8 KB	35.5 KB	-0.2 KB

function	head	change
`pgdog::frontend::client::Client::run::{{closure}}`	7.4 KB	-0.2 KB
`pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:`	5.8 KB	+0.1 KB
`pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}`	5.0 KB	+0.1 KB
`pgdog::frontend::router::parser::query::select::<impl pgdog::frontend::router::parser::que`	4.1 KB	+0.1 KB
`tokio::runtime::task::raw::poll`	3.8 KB	+0.0 KB