[jkaczman]

Follow up work to try to improve accuracy of microbench instructions in reference to #2003 seeing a +1.54% increase for a measure that shouldn't have been affected by that PR.

After some investigation, this seems to be because our LRU caches hash with foldhash, which builds a hash seed from code addresses (as a source of randomness). My guess is that this can change the order that we free cache entries in, and with that differs the work of all subsequent malloc calls.

Reference to their code that does this: https://github.com/orlp/foldhash/blob/77d8e3dae0d43abe65753e888b9e74efbe4ee3f7/src/seed.rs#L150-L156

Now, in the microbench, the LRU caches hash with a fixed seed (via foldhash::fast::FixedState, which they recommend for determinism).

This doesn't affect production builds.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[levkk]

You could make it conditional, i.e., only if bench feature is enabled. Although LLVM will probably remove it anyway during compilation / dead code elimination.

[github-actions]

Metal bench (arm64) passed. All 475 measures within bounds.

suite	throughput	cpu/txn	user cycles/txn	user instr/txn	kernel cycles/txn	kernel instr/txn	ctx/txn
pooler		19.65 (-0.6% ± 1.4%)	19,416 (-1.3% ± 0.8%)	32,015 (+0.0% ± 0.04%)	31,180 (-0.2% ± 3.0%)	50,961 (+0.3% ± 0.5%)
lb		20.46 (-0.3% ± 1.8%)	20,141 (-0.2% ± 1.0%)	32,911 (+0.0% ± 0.04%)	32,371 (-0.3% ± 3.4%)	52,107 (+0.0% ± 0.4%)
sharding-w2		33.49 (+0.3% ± 2.7%)	45,322 (-0.0% ± 2.3%)	97,446 (+0.0% ± 0.04%)	42,176 (+0.9% ± 4.2%)	53,584 (-0.0% ± 0.2%)	1.532 (-0.2% ± 0.5%)
sharding-w8	240,426 (+1.7% ± 2.0%)	29.89 (-2.0% ± 2.1%)	45,329 (-1.1% ± 2.0%)	52,993 (-0.0% ± 0.1%)	37,308 (-3.0% ± 2.2%)	42,390 (+0.1% ± 0.05%)	0.165 (+2.7% ± 0.5%)

Counters per txn

suite	frontend stall	l1i refill	backend stall
pooler	8,992 (-3.7% ± 2.0%)	2,806 (-1.6% ± 1.1%)
lb	9,493 (-1.5% ± 2.1%)	2,882 (-0.7% ± 1.1%)
sharding-w2	19,697 (+0.1% ± 5.7%)	4,323 (+0.2% ± 3.9%)
sharding-w8	21,497 (-2.5% ± 2.7%)	4,335 (-0.5% ± 1.7%)

Microbench: all 462 measures within bounds.

Hot code per txn

path	base	head	change
pooler	113.1 KB	112.6 KB	-0.5 KB
sharding-w2	166.8 KB	165.5 KB	-1.3 KB

pooler:

crate	base	head	change
pgdog::frontend::client::query_engine	19.8 KB	20.0 KB	+0.2 KB
tokio	18.5 KB	18.8 KB	+0.2 KB
pgdog::backend::pool	17.6 KB	17.6 KB	+0.0 KB
aws-lc (TLS crypto)	10.4 KB	10.2 KB	-0.2 KB
rustls (TLS)	8.4 KB	8.4 KB	-0.1 KB
pgdog::frontend (other)	8.0 KB	8.0 KB	+0.0 KB
pgdog::backend::server	7.1 KB	7.2 KB	+0.1 KB
other	6.6 KB	6.5 KB	-0.1 KB
everything else	16.6 KB	15.9 KB	-0.8 KB

function	head	change
pgdog::frontend::client::Client::run::{{closure}}	5.6 KB	+0.0 KB
pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:	5.4 KB	+0.0 KB
pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}	4.0 KB	+0.1 KB
tokio::runtime::task::raw::poll	3.2 KB	+0.1 KB
pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:	3.0 KB	+0.1 KB

sharding-w2:

crate	base	head	change
pgdog::frontend::router	28.8 KB	28.8 KB	+0.0 KB
pgdog::frontend::client::query_engine	21.1 KB	20.9 KB	-0.2 KB
pgdog::backend::pool	18.1 KB	18.4 KB	+0.4 KB
tokio	18.9 KB	18.4 KB	-0.4 KB
aws-lc (TLS crypto)	13.2 KB	13.1 KB	-0.2 KB
other	9.8 KB	9.6 KB	-0.2 KB
pgdog::frontend (other)	8.8 KB	8.6 KB	-0.2 KB
rustls (TLS)	8.1 KB	8.4 KB	+0.2 KB
everything else	40.0 KB	39.3 KB	-0.7 KB

function	head	change
pgdog::frontend::client::Client::run::{{closure}}	6.0 KB	-0.1 KB
pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:	5.3 KB	-0.1 KB
pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}	4.1 KB	-0.1 KB
pgdog::frontend::router::parser::query::select::<impl pgdog::frontend::router::parser::que	3.5 KB	+0.2 KB
tokio::runtime::task::raw::poll	3.1 KB	-0.1 KB

lb flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

microbench flamegraph vs 81a9f08

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Open interactive.

pooler flamegraph vs 81a9f08

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Open interactive.

sharding-w2 flamegraph vs 81a9f08

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Open interactive.

sharding-w8 flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

Logs

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

Compared 13b6db7 with 81a9f08 on m8g.metal-24xl (spot).

[github-actions]

Metal bench (x86) passed. All 475 measures within bounds.

suite	throughput	cpu/txn	user cycles/txn	user instr/txn	kernel cycles/txn	kernel instr/txn	ctx/txn
pooler		25.93 (+0.3% ± 0.2%)	19,167 (+0.6% ± 0.10%)	33,948 (-0.0% ± 0.1%)	33,317 (+0.3% ± 0.4%)	36,534 (+0.1% ± 0.8%)
lb		26.31 (+0.2% ± 0.2%)	19,660 (+0.6% ± 0.1%)	34,932 (+0.1% ± 0.07%)	33,429 (+0.1% ± 0.3%)	37,306 (+0.4% ± 0.4%)
sharding-w2		42.01 (+0.1% ± 1.2%)	47,516 (+0.1% ± 0.8%)	101,365 (-0.0% ± 0.07%)	38,067 (+0.2% ± 1.7%)	40,189 (-0.0% ± 0.1%)	1.528 (-0.2% ± 0.6%)
sharding-w8	207,984 (-0.2% ± 0.4%)	32.73 (+0.2% ± 0.7%)	45,625 (+0.2% ± 1.5%)	55,678 (+0.0% ± 0.05%)	31,204 (+0.1% ± 0.5%)	32,504 (+0.0% ± 0.07%)	0.1721 (-0.1% ± 2.6%)

Counters per txn

suite	frontend stall	l1i refill	backend stall
pooler	3,875 (+3.6% ± 0.6%)	1,208 (+1.6% ± 0.6%)	36,860 (-0.3% ± 0.5%)
lb	3,982 (+3.5% ± 0.8%)	1,236 (+1.2% ± 1.2%)	37,737 (-0.3% ± 0.6%)
sharding-w2	6,582 (-5.1% ± 0.9%)	1,676 (-0.2% ± 0.9%)	112,486 (+2.2% ± 2.4%)
sharding-w8	3,592 (-2.9% ± 0.8%)	1,030 (-0.2% ± 1.4%)	170,747 (+0.7% ± 2.6%)

Microbench: all 462 measures within bounds.

Hot code per txn

path	base	head	change
pooler	111.3 KB	111.2 KB	-0.1 KB
sharding-w2	164.6 KB	165.0 KB	+0.4 KB

pooler:

crate	base	head	change
pgdog::frontend::client::query_engine	21.0 KB	21.1 KB	+0.1 KB
tokio	18.4 KB	18.6 KB	+0.2 KB
pgdog::backend::pool	18.5 KB	18.1 KB	-0.4 KB
pgdog::frontend (other)	9.4 KB	9.5 KB	+0.1 KB
aws-lc (TLS crypto)	8.9 KB	8.8 KB	-0.1 KB
rustls (TLS)	7.9 KB	7.9 KB	+0.0 KB
pgdog::backend::server	7.0 KB	7.0 KB	+0.0 KB
other	6.0 KB	5.9 KB	-0.1 KB
everything else	14.2 KB	14.4 KB	+0.2 KB

function	head	change
pgdog::frontend::client::Client::run::{{closure}}	7.3 KB	+0.1 KB
pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:	6.1 KB	+0.0 KB
pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}	5.0 KB	+0.2 KB
tokio::runtime::task::raw::poll	3.6 KB	-0.1 KB
pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:	3.1 KB	-0.2 KB

sharding-w2:

crate	base	head	change
pgdog::frontend::router	28.6 KB	28.9 KB	+0.3 KB
pgdog::frontend::client::query_engine	22.4 KB	22.2 KB	-0.1 KB
tokio	18.2 KB	18.8 KB	+0.6 KB
pgdog::backend::pool	18.6 KB	18.6 KB	+0.1 KB
other	10.2 KB	10.6 KB	+0.4 KB
pgdog::frontend (other)	10.4 KB	10.6 KB	+0.1 KB
aws-lc (TLS crypto)	10.4 KB	10.4 KB	+0.0 KB
pgdog::backend::server	7.9 KB	7.8 KB	-0.1 KB
everything else	38.0 KB	37.2 KB	-0.8 KB

function	head	change
pgdog::frontend::client::Client::run::{{closure}}	8.1 KB	+0.1 KB
pgdog::frontend::client::query_engine::query::<impl pgdog::frontend::client::query_engine:	6.1 KB	+0.1 KB
pgdog::frontend::client::query_engine::QueryEngine::handle::{{closure}}	4.6 KB	-0.1 KB
pgdog::frontend::router::parser::query::select::<impl pgdog::frontend::router::parser::que	4.3 KB	+0.1 KB
tokio::runtime::task::raw::poll	4.2 KB	+0.4 KB

lb flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

microbench flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

pooler flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

sharding-w2 flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

sharding-w8 flamegraph vs 81a9f08

Open interactive for hover, zoom and search.

Open interactive.

Logs

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

Compared 13b6db7 with 81a9f08 on m7i.metal-48xl (spot).