diff --git a/Cargo.lock b/Cargo.lock
index 864538a57a4..4b89fb3d389 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -7499,6 +7499,7 @@ dependencies = [
  "bitflags 2.10.0",
  "bytes",
  "crc32c",
+ "criterion",
  "env_logger 0.10.2",
  "futures",
  "itertools 0.12.1",
diff --git a/crates/commitlog/Cargo.toml b/crates/commitlog/Cargo.toml
index 1f538453311..1e13a97ff11 100644
--- a/crates/commitlog/Cargo.toml
+++ b/crates/commitlog/Cargo.toml
@@ -46,6 +46,7 @@ pretty_assertions.workspace = true
 # Also enable 'test' feature, so integration tests can use the helpers.
 spacetimedb-commitlog = { path = ".", features = ["test", "streaming"] }
 
+criterion.workspace = true
 env_logger.workspace = true
 once_cell.workspace = true
 pretty_assertions = { workspace = true, features = ["unstable"] }
@@ -57,3 +58,7 @@ tokio-stream = { version = "0.1.17", features = ["fs"] }
 
 [lints]
 workspace = true
+
+[[bench]]
+name = "write"
+harness = false
diff --git a/crates/commitlog/benches/common/mod.rs b/crates/commitlog/benches/common/mod.rs
new file mode 100644
index 00000000000..d9d780b68f9
--- /dev/null
+++ b/crates/commitlog/benches/common/mod.rs
@@ -0,0 +1,23 @@
+use spacetimedb_sats::buffer::BufWriter;
+
+/// A commitlog payload consisting of uninterpreted bytes.
+pub struct Payload(Box<[u8]>);
+
+impl Payload {
+    pub fn new(bytes: impl Into<Box<[u8]>>) -> Self {
+        Self(bytes.into())
+    }
+}
+
+impl spacetimedb_commitlog::Encode for Payload {
+    fn encode_record<W: BufWriter>(&self, writer: &mut W) {
+        writer.put_u64(self.0.len() as _);
+        writer.put_slice(&self.0[..]);
+    }
+}
+
+impl spacetimedb_commitlog::Encode for &Payload {
+    fn encode_record<W: BufWriter>(&self, writer: &mut W) {
+        (*self).encode_record(writer)
+    }
+}
diff --git a/crates/commitlog/benches/write.rs b/crates/commitlog/benches/write.rs
new file mode 100644
index 00000000000..601767be620
--- /dev/null
+++ b/crates/commitlog/benches/write.rs
@@ -0,0 +1,130 @@
+use core::fmt;
+use std::num::NonZeroU16;
+
+use criterion::{criterion_group, criterion_main, BenchmarkId, Criterion, SamplingMode, Throughput};
+use spacetimedb_commitlog::{Commitlog, Options};
+use spacetimedb_paths::{server::CommitLogDir, FromPathUnchecked as _};
+use tempfile::tempdir_in;
+
+mod common;
+use common::Payload;
+
+struct Params {
+    payloads: Box<[Payload]>,
+    txs_per_commit: NonZeroU16,
+    total_appends: u64,
+    fsync_every: u64,
+}
+
+impl Params {
+    fn with_payloads(payloads: impl Into<Box<[Payload]>>) -> Self {
+        Self {
+            payloads: payloads.into(),
+            txs_per_commit: NonZeroU16::new(1).unwrap(),
+            total_appends: 1_000,
+            fsync_every: 32,
+        }
+    }
+}
+
+impl fmt::Display for Params {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "n={} tx/commit={} fsync={}",
+            self.total_appends, self.txs_per_commit, self.fsync_every
+        )
+    }
+}
+
+fn bench_append(c: &mut Criterion, label: &str, params: Params) {
+    let id = BenchmarkId::from_parameter(&params);
+    c.benchmark_group(label)
+        .sample_size(10)
+        .sampling_mode(SamplingMode::Flat)
+        .throughput(Throughput::Elements(params.total_appends))
+        .bench_with_input(
+            id,
+            &params,
+            |b,
+             Params {
+                 payloads,
+                 txs_per_commit,
+                 total_appends,
+                 fsync_every,
+             }| {
+                let tmp = tempdir_in(".").unwrap();
+                let clog = Commitlog::open(
+                    CommitLogDir::from_path_unchecked(tmp.path()),
+                    Options {
+                        max_records_in_commit: *txs_per_commit,
+                        ..<_>::default()
+                    },
+                    None,
+                )
+                .unwrap();
+
+                b.iter(|| {
+                    let mut payloads = payloads.iter().cycle();
+                    for i in 0..*total_appends {
+                        let payload = payloads.next().unwrap();
+                        let mut retry = Some(payload);
+                        while let Some(txdata) = retry.take() {
+                            if let Err(txdata) = clog.append(txdata) {
+                                clog.flush().unwrap();
+                                retry = Some(txdata);
+                            }
+                        }
+                        if i % fsync_every == 0 {
+                            clog.flush_and_sync().unwrap();
+                        }
+                    }
+                    clog.flush_and_sync().unwrap();
+                })
+            },
+        );
+}
+
+fn baseline(c: &mut Criterion) {
+    let params = Params::with_payloads([Payload::new([b'z'; 64])]);
+    bench_append(c, "baseline", params);
+}
+
+fn large_payload(c: &mut Criterion) {
+    let params = Params::with_payloads([Payload::new([b'z'; 4096])]);
+    bench_append(c, "large payload", params);
+}
+
+fn mixed_payloads(c: &mut Criterion) {
+    let params = Params::with_payloads([
+        Payload::new([b'a'; 64]),
+        Payload::new([b'b'; 512]),
+        Payload::new([b'c'; 1024]),
+        Payload::new([b'd'; 4096]),
+        Payload::new([b'e'; 8102]),
+    ]);
+    bench_append(c, "mixed payloads", params);
+}
+
+fn mixed_payloads_with_batching(c: &mut Criterion) {
+    let params = Params {
+        txs_per_commit: NonZeroU16::new(16).unwrap(),
+        ..Params::with_payloads([
+            Payload::new([b'a'; 64]),
+            Payload::new([b'b'; 512]),
+            Payload::new([b'c'; 1024]),
+            Payload::new([b'd'; 4096]),
+            Payload::new([b'e'; 8102]),
+        ])
+    };
+    bench_append(c, "mixed payloads with batching", params);
+}
+
+criterion_group!(
+    benches,
+    baseline,
+    large_payload,
+    mixed_payloads,
+    mixed_payloads_with_batching
+);
+criterion_main!(benches);