initial commit

Signed-off-by: Alex Chi <iskyzh@gmail.com>
2022-12-23 14:29:32 -05:00
commit 68303e99b8
17 changed files with 849 additions and 0 deletions
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -0,0 +1,3 @@
+[alias]
+xtask = "run --package mini-lsm-xtask --"
+x = "run --package mini-lsm-xtask --"
--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "editor.formatOnSave": true
+}
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -0,0 +1,419 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "anyhow"
+version = "1.0.68"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2cb2f989d18dd141ab8ae82f64d1a8cdd37e0840f73a406896cf5e99502fab61"
+
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "bytes"
+version = "1.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dfb24e866b15a1af2a1b663f10c6b6b8f397a84aadb828f12e5b289ec23a3a3c"
+
+[[package]]
+name = "cc"
+version = "1.0.78"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a20104e2335ce8a659d6dd92a51a767a0c062599c73b343fd152cb401e828c3d"
+
+[[package]]
+name = "clap"
+version = "4.0.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7db700bc935f9e43e88d00b0850dae18a63773cfbec6d8e070fccf7fef89a39"
+dependencies = [
+ "bitflags",
+ "clap_derive",
+ "clap_lex",
+ "is-terminal",
+ "once_cell",
+ "strsim",
+ "termcolor",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.0.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0177313f9f02afc995627906bbd8967e2be069f5261954222dac78290c2b9014"
+dependencies = [
+ "heck",
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "clap_lex"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0d4198f73e42b4936b35b5bb248d81d2b595ecb170da0bac7655c54eedfa8da8"
+dependencies = [
+ "os_str_bytes",
+]
+
+[[package]]
+name = "console"
+version = "0.15.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c050367d967ced717c04b65d8c619d863ef9292ce0c5760028655a2fb298718c"
+dependencies = [
+ "encode_unicode",
+ "lazy_static",
+ "libc",
+ "terminal_size",
+ "unicode-width",
+ "winapi",
+]
+
+[[package]]
+name = "duct"
+version = "0.13.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37ae3fc31835f74c2a7ceda3aeede378b0ae2e74c8f1c36559fcc9ae2a4e7d3e"
+dependencies = [
+ "libc",
+ "once_cell",
+ "os_pipe",
+ "shared_child",
+]
+
+[[package]]
+name = "encode_unicode"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a357d28ed41a50f9c765dbfe56cbc04a64e53e5fc58ba79fbc34c10ef3df831f"
+
+[[package]]
+name = "errno"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f639046355ee4f37944e44f60642c6f3a7efa3cf6b78c78a0d989a8ce6c396a1"
+dependencies = [
+ "errno-dragonfly",
+ "libc",
+ "winapi",
+]
+
+[[package]]
+name = "errno-dragonfly"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa68f1b12764fab894d2755d2518754e71b4fd80ecfb822714a1206c2aab39bf"
+dependencies = [
+ "cc",
+ "libc",
+]
+
+[[package]]
+name = "heck"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2540771e65fc8cb83cd6e8a237f70c319bd5c29f78ed1084ba5d50eeac86f7f9"
+
+[[package]]
+name = "hermit-abi"
+version = "0.2.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee512640fe35acbfb4bb779db6f0d80704c2cacfa2e39b601ef3e3f47d1ae4c7"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "io-lifetimes"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46112a93252b123d31a119a8d1a1ac19deac4fac6e0e8b0df58f0d4e5870e63c"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "is-terminal"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "28dfb6c8100ccc63462345b67d1bbc3679177c75ee4bf59bf29c8b1d110b8189"
+dependencies = [
+ "hermit-abi",
+ "io-lifetimes",
+ "rustix",
+ "windows-sys",
+]
+
+[[package]]
+name = "lazy_static"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
+
+[[package]]
+name = "libc"
+version = "0.2.139"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "201de327520df007757c1f0adce6e827fe8562fbc28bfd9c15571c66ca1f5f79"
+
+[[package]]
+name = "linux-raw-sys"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f051f77a7c8e6957c0696eac88f26b0117e54f52d3fc682ab19397a8812846a4"
+
+[[package]]
+name = "mini-lsm"
+version = "0.1.0"
+dependencies = [
+ "bytes",
+]
+
+[[package]]
+name = "mini-lsm-xtask"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "clap",
+ "console",
+ "duct",
+]
+
+[[package]]
+name = "once_cell"
+version = "1.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "86f0b0d4bf799edbc74508c1e8bf170ff5f41238e5f8225603ca7caaae2b7860"
+
+[[package]]
+name = "os_pipe"
+version = "1.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c6a252f1f8c11e84b3ab59d7a488e48e4478a93937e027076638c49536204639"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "os_str_bytes"
+version = "6.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b7820b9daea5457c9f21c69448905d723fbd21136ccf521748f23fd49e723ee"
+
+[[package]]
+name = "proc-macro-error"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+dependencies = [
+ "proc-macro-error-attr",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro-error-attr"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.49"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "57a8eca9f9c4ffde41714334dee777596264c7825420f521abc92b5b5deb63a5"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8856d8364d252a14d474036ea1358d63c9e6965c8e5c1885c18f73d70bff9c7b"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "rustix"
+version = "0.36.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a3807b5d10909833d3e9acd1eb5fb988f79376ff10fce42937de71a449c4c588"
+dependencies = [
+ "bitflags",
+ "errno",
+ "io-lifetimes",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
+[[package]]
+name = "shared_child"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0d94659ad3c2137fef23ae75b03d5241d633f8acded53d672decfa0e6e0caef"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
+[[package]]
+name = "strsim"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
+
+[[package]]
+name = "syn"
+version = "1.0.107"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1f4064b5b16e03ae50984a5a8ed5d4f8803e6bc1fd170a3cda91a1be4b18e3f5"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "termcolor"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bab24d30b911b2376f3a13cc2cd443142f0c81dda04c118693e35b3835757755"
+dependencies = [
+ "winapi-util",
+]
+
+[[package]]
+name = "terminal_size"
+version = "0.1.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "633c1a546cee861a1a6d0dc69ebeca693bf4296661ba7852b9d21d159e0506df"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "84a22b9f218b40614adcb3f4ff08b703773ad44fa9423e4e0d346d5db86e4ebc"
+
+[[package]]
+name = "unicode-width"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c0edd1e5b14653f783770bce4a4dabb4a5108a5370a5f5d8cfe8710c361f6c8b"
+
+[[package]]
+name = "version_check"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-util"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
+dependencies = [
+ "winapi",
+]
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
+
+[[package]]
+name = "windows-sys"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a3e1820f08b8513f676f7ab6c1f99ff312fb97b553d30ff4dd86f9f15728aa7"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "41d2aa71f6f0cbe00ae5167d90ef3cfe66527d6f613ca78ac8024c3ccab9a19e"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dd0f252f5a35cac83d6311b2e795981f5ee6e67eb1f9a7f64eb4500fbc4dcdb4"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fbeae19f6716841636c28d695375df17562ca208b2b7d0dc47635a50ae6c5de7"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "84c12f65daa39dd2babe6e442988fc329d6243fdce47d7d2d155b8d874862246"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bf7b1b21b5362cbc318f686150e5bcea75ecedc74dd157d874d754a2ca44b0ed"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09d525d2ba30eeb3297665bd434a54297e4170c7f1a44cad4ef58095b4cd2028"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.42.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40009d85759725a34da6d89a94e63d7bdc50a862acf0dbc7c8e488f1edcb6f5"
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -0,0 +1,13 @@
+[workspace]
+members = [
+  "mini-lsm",
+  "xtask"
+]
+
+[workspace.package]
+version = "0.1.0"
+edition = "2021"
+homepage = "https://github.com/skyzh/mini-lsm"
+keywords = ["storage", "database", "tutorial"]
+license = "Apache-2.0"
+repository = "https://github.com/skyzh/mini-lsm"
--- a/mini-lsm-book/.gitignore
+++ b/mini-lsm-book/.gitignore
@@ -0,0 +1 @@
+book
--- a/mini-lsm-book/book.toml
+++ b/mini-lsm-book/book.toml
@@ -0,0 +1,10 @@
+[book]
+authors = ["Alex Chi"]
+language = "en"
+multilingual = false
+src = "src"
+title = "LSM in a Week"
+
+[preprocessor.toc]
+command = "mdbook-toc"
+renderer = ["html"]
--- a/mini-lsm-book/src/SUMMARY.md
+++ b/mini-lsm-book/src/SUMMARY.md
@@ -0,0 +1,3 @@
+# Summary
+
+- [Chapter 1](./chapter_1.md)
--- a/mini-lsm-book/src/chapter_1.md
+++ b/mini-lsm-book/src/chapter_1.md
@@ -0,0 +1 @@
+# Chapter 1
--- a/mini-lsm/Cargo.toml
+++ b/mini-lsm/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "mini-lsm"
+version = { workspace = true }
+edition = { workspace = true }
+homepage = { workspace = true }
+keywords = { workspace = true }
+license = { workspace = true }
+repository = { workspace = true }
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bytes = "1"
--- a/mini-lsm/src/block.rs
+++ b/mini-lsm/src/block.rs
@@ -0,0 +1,132 @@
+mod builder;
+mod iterator;
+
+use bytes::{Buf, BufMut, Bytes};
+
+pub use builder::BlockBuilder;
+pub use iterator::BlockIterator;
+
+pub const SIZEOF_U16: usize = std::mem::size_of::<u16>();
+
+/// A block is the smallest unit of read and caching in LSM tree. It is a collection of sorted key-value pairs.
+pub struct Block {
+    pub(self) data: Vec<u8>,
+    pub(self) offsets: Vec<u16>,
+}
+
+impl Block {
+    pub fn encode(&self) -> Bytes {
+        let mut buf = self.data.clone();
+        let offsets_len = self.offsets.len();
+        for offset in &self.offsets {
+            buf.put_u16(*offset);
+        }
+        buf.put_u16(offsets_len as u16);
+        buf.into()
+    }
+
+    pub fn decode(data: &[u8]) -> Self {
+        let entry_offsets_len = (&data[data.len() - SIZEOF_U16..]).get_u16() as usize;
+        let data_end = data.len() - SIZEOF_U16 - entry_offsets_len * SIZEOF_U16;
+        let offsets_raw = &data[data_end..data.len() - SIZEOF_U16];
+        let offsets = offsets_raw
+            .chunks(SIZEOF_U16)
+            .map(|mut x| x.get_u16())
+            .collect();
+        let data = data[0..data_end].to_vec();
+        Self { data, offsets }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::sync::Arc;
+
+    use super::{builder::BlockBuilder, iterator::BlockIterator, *};
+
+    #[test]
+    fn test_block_build_single_key() {
+        let mut builder = BlockBuilder::new(16);
+        assert!(builder.add(b"233", b"233333"));
+        builder.build();
+    }
+
+    #[test]
+    fn test_block_build_full() {
+        let mut builder = BlockBuilder::new(16);
+        assert!(builder.add(b"11", b"11"));
+        assert!(!builder.add(b"22", b"22"));
+        builder.build();
+    }
+
+    fn key_of(idx: usize) -> Vec<u8> {
+        format!("key_{:03}", idx).into_bytes()
+    }
+
+    fn value_of(idx: usize) -> Vec<u8> {
+        format!("value_{:010}", idx).into_bytes()
+    }
+
+    fn num_of_keys() -> usize {
+        100
+    }
+
+    fn generate_block() -> Block {
+        let mut builder = BlockBuilder::new(10000);
+        for idx in 0..num_of_keys() {
+            let key = key_of(idx);
+            let value = value_of(idx);
+            assert!(builder.add(&key[..], &value[..]));
+        }
+        builder.build()
+    }
+
+    #[test]
+    fn test_block_build_all() {
+        generate_block();
+    }
+
+    #[test]
+    fn test_block_encode() {
+        let block = generate_block();
+        block.encode();
+    }
+
+    #[test]
+    fn test_block_decode() {
+        let block = generate_block();
+        let encoded = block.encode();
+        let decoded_block = Block::decode(&encoded);
+        assert_eq!(block.offsets, decoded_block.offsets);
+        assert_eq!(block.data, decoded_block.data);
+    }
+
+    fn as_bytes(x: &[u8]) -> Bytes {
+        Bytes::copy_from_slice(x)
+    }
+
+    #[test]
+    fn test_block_iterator() {
+        let block = Arc::new(generate_block());
+        let mut iter = BlockIterator::create_and_seek_to_first(block);
+        for i in 0..num_of_keys() {
+            let key = iter.key();
+            let value = iter.value();
+            assert_eq!(
+                key,
+                key_of(i),
+                "expected key: {:?}, actual key: {:?}",
+                as_bytes(&key_of(i)),
+                as_bytes(key)
+            );
+            assert_eq!(
+                value,
+                value_of(i),
+                "expected value: {:?}, actual value: {:?}",
+                as_bytes(&value_of(i)),
+                as_bytes(value)
+            );
+            iter.next();
+        }
+    }
+}
--- a/mini-lsm/src/block/builder.rs
+++ b/mini-lsm/src/block/builder.rs
@@ -0,0 +1,57 @@
+use bytes::BufMut;
+
+use super::{Block, SIZEOF_U16};
+
+/// Builds a block
+pub struct BlockBuilder {
+    offsets: Vec<u16>,
+    data: Vec<u8>,
+    target_size: usize,
+}
+
+impl BlockBuilder {
+    /// Creates a new block builder
+    pub fn new(target_size: usize) -> Self {
+        Self {
+            offsets: Vec::new(),
+            data: Vec::new(),
+            target_size,
+        }
+    }
+
+    fn estimated_size(&self) -> usize {
+        self.offsets.len() * SIZEOF_U16 + self.data.len() + SIZEOF_U16
+    }
+
+    /// Adds a key-value pair to the block
+    #[must_use]
+    pub fn add(&mut self, key: &[u8], value: &[u8]) -> bool {
+        assert!(!key.is_empty(), "key must not be empty");
+        if self.estimated_size() + key.len() + value.len() + SIZEOF_U16 * 3 > self.target_size
+            && !self.is_empty()
+        {
+            return false;
+        }
+        self.offsets.push(self.data.len() as u16);
+        self.data.put_u16(key.len() as u16);
+        self.data.put(key);
+        self.data.put_u16(value.len() as u16);
+        self.data.put(value);
+        true
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.offsets.is_empty()
+    }
+
+    /// Builds a block
+    pub fn build(self) -> Block {
+        if self.is_empty() {
+            panic!("block should not be empty");
+        }
+        Block {
+            data: self.data,
+            offsets: self.offsets,
+        }
+    }
+}
--- a/mini-lsm/src/block/iterator.rs
+++ b/mini-lsm/src/block/iterator.rs
@@ -0,0 +1,110 @@
+use std::sync::Arc;
+
+use bytes::Buf;
+
+use super::Block;
+
+pub struct BlockIterator {
+    block: Arc<Block>,
+    key: Vec<u8>,
+    value: Vec<u8>,
+    idx: usize,
+}
+
+impl BlockIterator {
+    fn new(block: Arc<Block>) -> Self {
+        Self {
+            block,
+            key: Vec::new(),
+            value: Vec::new(),
+            idx: 0,
+        }
+    }
+
+    pub fn create_and_seek_to_first(block: Arc<Block>) -> Self {
+        let mut iter = Self::new(block);
+        iter.seek_to_first();
+        iter
+    }
+
+    pub fn create_and_seek_to_key(block: Arc<Block>, key: &[u8]) -> Self {
+        let mut iter = Self::new(block);
+        iter.seek_to_key(key);
+        iter
+    }
+
+    pub fn key(&self) -> &[u8] {
+        debug_assert!(!self.key.is_empty(), "invalid iterator");
+        &self.key
+    }
+
+    pub fn value(&self) -> &[u8] {
+        debug_assert!(!self.key.is_empty(), "invalid iterator");
+        &self.value
+    }
+
+    pub fn is_valid(&self) -> bool {
+        !self.key.is_empty()
+    }
+
+    pub fn seek_to_first(&mut self) {
+        self.seek_to(0);
+    }
+
+    pub fn seek_to_last(&mut self) {
+        self.seek_to(self.block.offsets.len() - 1);
+    }
+
+    pub fn len(&self) -> usize {
+        self.block.offsets.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.block.offsets.is_empty()
+    }
+
+    pub fn seek_to(&mut self, idx: usize) {
+        if idx >= self.block.offsets.len() {
+            self.key.clear();
+            self.value.clear();
+            return;
+        }
+        let offset = self.block.offsets[idx] as usize;
+        self.seek_to_offset(offset);
+        self.idx = idx;
+    }
+
+    pub fn next(&mut self) {
+        self.idx += 1;
+        self.seek_to(self.idx);
+    }
+
+    fn seek_to_offset(&mut self, offset: usize) {
+        let mut entry = &self.block.data[offset..];
+        let key_len = entry.get_u16() as usize;
+        let key = entry[..key_len].to_vec();
+        entry.advance(key_len);
+        self.key.clear();
+        self.key.extend(key);
+        let value_len = entry.get_u16() as usize;
+        let value = entry[..value_len].to_vec();
+        entry.advance(value_len);
+        self.value.clear();
+        self.value.extend(value);
+    }
+
+    pub fn seek_to_key(&mut self, key: &[u8]) {
+        let mut low = 0;
+        let mut high = self.block.offsets.len();
+        while low < high {
+            let mid = low + (high - low) / 2;
+            self.seek_to(mid);
+            assert!(self.is_valid());
+            match self.key().cmp(key) {
+                std::cmp::Ordering::Less => low = mid + 1,
+                std::cmp::Ordering::Greater => high = mid,
+                std::cmp::Ordering::Equal => return,
+            }
+        }
+    }
+}
--- a/mini-lsm/src/lib.rs
+++ b/mini-lsm/src/lib.rs
@@ -0,0 +1 @@
+pub mod block;
--- a/1
+++ b/1
@@ -0,0 +1 @@
+nightly-2022-11-11
--- a/xtask/Cargo.toml
+++ b/xtask/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+name = "mini-lsm-xtask"
+version = { workspace = true }
+edition = { workspace = true }
+homepage = { workspace = true }
+keywords = { workspace = true }
+license = { workspace = true }
+repository = { workspace = true }
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1"
+console = "0.15"
+clap = { version = "4", features = ["derive"] }
+duct = "0.13"
--- a/xtask/src/main.rs
+++ b/xtask/src/main.rs
@@ -0,0 +1,65 @@
+use std::path::PathBuf;
+
+use anyhow::{anyhow, Result};
+use clap::Parser;
+use console::style;
+use duct::cmd;
+
+#[derive(clap::Subcommand, Debug)]
+enum Action {
+    /// Check.
+    Check,
+    /// Install necessary tools for development.
+    InstallTools,
+    /// Show environment variables.
+    Show,
+}
+
+/// Simple program to greet a person
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+struct Args {
+    #[command(subcommand)]
+    action: Action,
+}
+
+fn switch_to_workspace_root() -> Result<()> {
+    std::env::set_current_dir(
+        PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+            .parent()
+            .ok_or_else(|| anyhow!("failed to find the workspace root"))?,
+    )?;
+    Ok(())
+}
+
+fn main() -> Result<()> {
+    let args = Args::parse();
+
+    match args.action {
+        Action::InstallTools => {
+            println!("{}", style("cargo install cargo-nextest").bold());
+            cmd!("cargo", "install", "cargo-nextest", "--locked").run()?;
+            println!("{}", style("cargo install mdbook mdbook-toc").bold());
+            cmd!("cargo", "install", "mdbook", "mdbook-toc", "--locked").run()?;
+        }
+        Action::Check => {
+            switch_to_workspace_root()?;
+            println!("{}", style("cargo fmt").bold());
+            cmd!("cargo", "fmt").run()?;
+            println!("{}", style("cargo check").bold());
+            cmd!("cargo", "check", "--all-targets").run()?;
+            println!("{}", style("cargo nextest run").bold());
+            cmd!("cargo", "nextest", "run").run()?;
+            println!("{}", style("cargo clippy").bold());
+            cmd!("cargo", "clippy", "--all-targets").run()?;
+            println!("{}", style("mdbook build").bold());
+            cmd!("mdbook", "build").dir("mini-lsm-book").run()?;
+        }
+        Action::Show => {
+            println!("CARGO_MANIFEST_DIR={}", env!("CARGO_MANIFEST_DIR"));
+            println!("PWD={:?}", std::env::current_dir()?);
+        }
+    }
+
+    Ok(())
+}