Commitlog offset index (#1671)

Signed-off-by: Shubham Mishra <shubham@clockworklabs.io>
Co-authored-by: Kim Altintop <kim@eagain.io>

crates/bindings/tests/snapshots/deps__duplicate_deps.snap

@@ -2,6 +2,6 @@
 source: crates/bindings/tests/deps.rs
 expression: cargo tree -p spacetimedb -e no-dev -d --depth 0
 ---
-syn v1.0.109
+heck v0.4.1
 
-syn v2.0.39
+heck v0.5.0

crates/bindings/tests/snapshots/deps__spacetimedb_bindings_dependencies.snap

@@ -2,7 +2,7 @@
 source: crates/bindings/tests/deps.rs
 expression: "cargo tree -p spacetimedb -f {lib} -e no-dev"
 ---
-total crates: 60
+total crates: 62
 spacetimedb
 ├── bytemuck
 ├── derive_more
@@ -26,6 +26,12 @@ spacetimedb
 │   ├── libc
 │   ├── rand_chacha
 │   │   ├── ppv_lite86
+│   │   │   └── zerocopy
+│   │   │       ├── byteorder
+│   │   │       └── zerocopy_derive
+│   │   │           ├── proc_macro2 (*)
+│   │   │           ├── quote (*)
+│   │   │           └── syn (*)
 │   │   └── rand_core
 │   │       └── getrandom (*)
 │   └── rand_core (*)
@@ -42,10 +48,7 @@ spacetimedb
 │   │   ├── itertools
 │   │   │   └── either
 │   │   └── nohash_hasher
-│   └── syn
-│       ├── proc_macro2 (*)
-│       ├── quote (*)
-│       └── unicode_ident
+│   └── syn (*)
 ├── spacetimedb_bindings_sys
 │   └── spacetimedb_primitives (*)
 ├── spacetimedb_lib
@@ -65,7 +68,7 @@ spacetimedb
 │   │   │   ├── ahash
 │   │   │   │   ├── cfg_if
 │   │   │   │   ├── once_cell
-│   │   │   │   └── zerocopy
+│   │   │   │   └── zerocopy (*)
 │   │   │   │   [build-dependencies]
 │   │   │   │   └── version_check
 │   │   │   └── allocator_api2

crates/commitlog/Cargo.toml

@@ -15,9 +15,11 @@ bitflags.workspace = true
 crc32c.workspace = true
 itertools.workspace = true
 log.workspace = true
+memmap2 = "0.9.4"
 serde = { workspace = true, optional = true }
 spacetimedb-primitives.workspace = true
 spacetimedb-sats.workspace = true
+tempfile.workspace = true
 thiserror.workspace = true
 
 [dev-dependencies]

crates/commitlog/src/commitlog.rs

@@ -230,8 +230,8 @@ impl<R: Repo, T> Generic<R, T> {
                 } else {
                     let byte_offset = segment::Header::LEN as u64 + bytes_read;
                     debug!("truncating segment {segment} to {offset} at {byte_offset}");
-                    let file = self.repo.open_segment(segment)?;
-                    file.ftruncate(byte_offset)?;
+                    let mut file = self.repo.open_segment(segment)?;
+                    file.ftruncate(offset, byte_offset)?;
                     // Some filesystems require fsync after ftruncate.
                     file.fsync()?;
                     break;