├── .gitignore ├── Cargo.toml ├── LICENSE ├── README.md ├── description ├── entry.png ├── lanes.png ├── page.png └── writing.md ├── rustfmt.toml └── src └── lib.rs /.gitignore: -------------------------------------------------------------------------------- 1 | target/ 2 | **/*.rs.bk 3 | Cargo.lock 4 | description/writing.html 5 | description/graphics.html 6 | description/style.css 7 | -------------------------------------------------------------------------------- /Cargo.toml: -------------------------------------------------------------------------------- 1 | [package] 2 | authors = ["Kristoffer Ström "] 3 | edition = "2018" 4 | name = "appendix" 5 | version = "0.2.3" 6 | description = "Append-only, on-disk key-value index" 7 | documentation = "https://docs.rs/appendix/" 8 | keywords = ["index", "datastructure"] 9 | license = "GPL-3.0" 10 | 11 | [dependencies] 12 | arrayvec = "0.4.10" 13 | bytemuck = "1.12.3" 14 | lazy_static = "1.2.0" 15 | memmap = "0.7.0" 16 | parking_lot = "0.7.1" 17 | seahash = "3.0.5" 18 | 19 | [dev-dependencies] 20 | rand = "0.6.4" 21 | tempfile = "3.0.5" 22 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU GENERAL PUBLIC LICENSE 2 | Version 3, 29 June 2007 3 | 4 | Copyright (C) 2007 Free Software Foundation, Inc. 5 | Everyone is permitted to copy and distribute verbatim copies 6 | of this license document, but changing it is not allowed. 7 | 8 | Preamble 9 | 10 | The GNU General Public License is a free, copyleft license for 11 | software and other kinds of works. 12 | 13 | The licenses for most software and other practical works are designed 14 | to take away your freedom to share and change the works. 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Interpretation of Sections 15 and 16. 613 | 614 | If the disclaimer of warranty and limitation of liability provided 615 | above cannot be given local legal effect according to their terms, 616 | reviewing courts shall apply local law that most closely approximates 617 | an absolute waiver of all civil liability in connection with the 618 | Program, unless a warranty or assumption of liability accompanies a 619 | copy of the Program in return for a fee. 620 | 621 | END OF TERMS AND CONDITIONS 622 | 623 | How to Apply These Terms to Your New Programs 624 | 625 | If you develop a new program, and you want it to be of the greatest 626 | possible use to the public, the best way to achieve this is to make it 627 | free software which everyone can redistribute and change under these terms. 628 | 629 | To do so, attach the following notices to the program. It is safest 630 | to attach them to the start of each source file to most effectively 631 | state the exclusion of warranty; and each file should have at least 632 | the "copyright" line and a pointer to where the full notice is found. 633 | 634 | Appendix, an append only on-disk key value store. 635 | Copyright (C) 2019 Kristoffer Ström 636 | 637 | This program is free software: you can redistribute it and/or modify 638 | it under the terms of the GNU General Public License as published by 639 | the Free Software Foundation, either version 3 of the License, or 640 | (at your option) any later version. 641 | 642 | This program is distributed in the hope that it will be useful, 643 | but WITHOUT ANY WARRANTY; without even the implied warranty of 644 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 645 | GNU General Public License for more details. 646 | 647 | You should have received a copy of the GNU General Public License 648 | along with this program. If not, see . 649 | 650 | Also add information on how to contact you by electronic and paper mail. 651 | 652 | If the program does terminal interaction, make it output a short 653 | notice like this when it starts in an interactive mode: 654 | 655 | Appendix Copyright (C) 2019 Kristoffer Ström 656 | This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. 657 | This is free software, and you are welcome to redistribute it 658 | under certain conditions; type `show c' for details. 659 | 660 | The hypothetical commands `show w' and `show c' should show the appropriate 661 | parts of the General Public License. Of course, your program's commands 662 | might be different; for a GUI interface, you would use an "about box". 663 | 664 | You should also get your employer (if you work as a programmer) or school, 665 | if any, to sign a "copyright disclaimer" for the program, if necessary. 666 | For more information on this, and how to apply and follow the GNU GPL, see 667 | . 668 | 669 | The GNU General Public License does not permit incorporating your program 670 | into proprietary programs. If your program is a subroutine library, you 671 | may consider it more useful to permit linking proprietary applications with 672 | the library. If this is what you want to do, use the GNU Lesser General 673 | Public License instead of this License. But first, please read 674 | . 675 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Appendix 2 | 3 | [Documentation](https://docs.rs/appendix/) 4 | 5 | An immutable, append-only, thread safe, on-disk index mapping `Copy` keys to `Copy` values. 6 | 7 | For a description see [this writeup](https://github.com/krl/appendix/blob/master/description/writing.md) -------------------------------------------------------------------------------- /description/entry.png: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/krl/appendix/897114a395f0e3b43dbbcc826c1b23c8b99e6896/description/entry.png -------------------------------------------------------------------------------- /description/lanes.png: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/krl/appendix/897114a395f0e3b43dbbcc826c1b23c8b99e6896/description/lanes.png -------------------------------------------------------------------------------- /description/page.png: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/krl/appendix/897114a395f0e3b43dbbcc826c1b23c8b99e6896/description/page.png -------------------------------------------------------------------------------- /description/writing.md: -------------------------------------------------------------------------------- 1 | # Writing an append-only, on-disk key-value store with lockless reads in Rust. 2 | 3 | Our goal for this blog post is to describe a key-value store with certain properties: 4 | 5 | * Persistant on-disk storage of key-value pairs. 6 | * Thread safety, should be `Send` + `Sync`. 7 | * Lockless reads across threads. 8 | * No single bottleneck lock while writing. 9 | 10 | # Immutability 11 | 12 | In order to implement all of this in about 400 lines, we give up on any mutability of already written keys. That is, when a key-value pair is written once, it will thereafter never change. 13 | 14 | We also have to make sure `K` and `V` are `Copy`, i.e Plain Old Data. 15 | 16 | # Datastructure 17 | 18 | The datastructure of choice in this implementation is a hash-array mapped trie (or HAMT for short). It can be thought of as a nested hash-table. 19 | 20 | The nodes of the trie consists of a series of Entries. 21 | 22 | ![Page memory layout](page.png "Page memory layout") 23 | 24 | The node sizes are defined as the amount of Entries that fit into a 4Kib page. (a common cache-page size) 25 | 26 | We will take a closer look at `Entry` here. 27 | 28 | ![Entry memory layout](entry.png "Entry memory layout") 29 | 30 | The first two fields should be self-explanatory, but what about `next` and the checksums? 31 | 32 | It turns out, since we are using memory-mapped files, the initial state of any region of a page will be all zeroes. If we did not have the checksums, an entry with `key` and `val` set to zero would be indistinguisable from a vacant entry in the node. 33 | 34 | The checksums also work as such, checksums, making sure any botched half-writes to the underlying medium will also be considered vacant. 35 | 36 | # Insertion method 37 | 38 | In order to quickly insert into the table without lock-contestation the initial search is carried out completely without locking by the following procedure. 39 | 40 | The root-node on page 0 is consulted, the key is hashed and it's slot is calculated. Here we have three possible outcomes for the corresponding entry: 41 | 42 | **1: The entry is invalid** 43 | 44 | * Just write a new `Entry` in place and end. 45 | 46 | **2: The `next` attribute is nonzero** 47 | 48 | * Recurse into the new page pointed to. 49 | 50 | **3: The `next` attribute is zero** 51 | 52 | * Create a new page, and modify the `next` value in the `Entry` 53 | 54 | # Locking 55 | 56 | When do we need to take locks on writing? 57 | 58 | ## Adding a new page 59 | 60 | In a relatively small number of cases, a new page has to be created. For this a lock must be taken, to update the page counter, and in certain cases creating new memory mapped files. The majority of writes doesn't touch this path. 61 | 62 | ## Modifing an entry 63 | 64 | When an entry is modified, either by assigning it a key-value pair or by updating it's next pointer, a corresponding lock must be taken. 65 | 66 | But which lock? Having one single lock for writes would be a bottleneck, but keeping individual locks for each page is unwieldly. 67 | 68 | To solve this problem we use a static array of mutexes like this: 69 | 70 | ```rust 71 | static SHARDS: [Mutex<()>; 1024] = Default::default() 72 | ``` 73 | 74 | (if only we had const generics that is) 75 | 76 | We then calculate a value from the page and slot offset of the entry, take that modulo 1024, and lock that mutex. 77 | 78 | This way, we have only a very small chance of two writes happening simultaneously in buckets with identical shard-index, and the bottleneck is avoided while still maintaining safety. 79 | 80 | # On-disk storage 81 | 82 | For the on-disk storage we're using memory mapped files. Let's have a look at their layout. 83 | 84 | ![Layot of memory-mapped files](lanes.png "Lanes") 85 | 86 | If the first memory map fits 32 pages, the second fits 64, and so on. This is so that we can have a finite amount of Mmaps and still not run out of space anytime soon. 87 | 88 | # Stress testing 89 | 90 | For stress testing, one of the tests spawns 8 writer and 8 reader threads and simultaneously writes and reads values in random order. I might consider more advanced test methods, but for now it's a proof of concept. 91 | 92 | # Lastly 93 | 94 | Check out the [docs](https://docs.rs/appendix/) 95 | 96 | Check out the code in [this repository](https://github.com/krl/appendix/) for the concrete implementation. 97 | 98 | For comments: [Reddit post](https://www.reddit.com/r/rust/comments/aiyzco/writing_an_appendonly_ondisk_keyvalue_store_with/) 99 | 100 | # Author 101 | 102 | Kristoffer Ström ** 103 | 104 | 105 | 106 | -------------------------------------------------------------------------------- /rustfmt.toml: -------------------------------------------------------------------------------- 1 | max_width = 80 2 | -------------------------------------------------------------------------------- /src/lib.rs: -------------------------------------------------------------------------------- 1 | #![deny(missing_docs)] 2 | //! An append-only, on-disk key-value index with lockless reads 3 | 4 | use bytemuck::Pod; 5 | 6 | use std::cell::UnsafeCell; 7 | use std::fs::OpenOptions; 8 | use std::hash::{Hash, Hasher}; 9 | use std::io; 10 | use std::marker::PhantomData; 11 | use std::mem; 12 | use std::ops::{Deref, DerefMut}; 13 | use std::path::{Path, PathBuf}; 14 | 15 | use arrayvec::ArrayVec; 16 | use lazy_static::lazy_static; 17 | use memmap::MmapMut; 18 | use parking_lot::{Mutex, MutexGuard}; 19 | use seahash::SeaHasher; 20 | 21 | const NUM_LANES: usize = 64; 22 | const NUM_SHARDS: usize = 1024; 23 | const PAGE_SIZE: usize = 4096; 24 | const FIRST_LANE_PAGES: usize = 64; 25 | 26 | // marker struct for shard-mutexes 27 | struct Shard; 28 | 29 | lazy_static! { 30 | static ref SHARDS: ArrayVec<[Mutex; NUM_SHARDS]> = { 31 | let mut locks = ArrayVec::new(); 32 | for _ in 0..NUM_SHARDS { 33 | locks.push(Mutex::new(Shard)) 34 | } 35 | locks 36 | }; 37 | } 38 | 39 | #[inline(always)] 40 | fn hash_val(t: &T) -> u64 { 41 | let mut hasher = SeaHasher::new(); 42 | t.hash(&mut hasher); 43 | hasher.finish() 44 | } 45 | 46 | enum Found<'a, K, V> { 47 | Some(&'a Entry), 48 | None(usize, usize, usize), 49 | Invalid(usize, usize, usize), 50 | } 51 | 52 | /// Marker type telling you your update was a no-op 53 | pub type AlreadyThere = bool; 54 | 55 | /// On-disk index structure mapping keys to values 56 | pub struct Index { 57 | lanes: UnsafeCell>, 58 | path: PathBuf, 59 | pages: Mutex, 60 | _marker: PhantomData<(K, V)>, 61 | } 62 | 63 | unsafe impl Send for Index 64 | where 65 | K: Send, 66 | V: Send, 67 | { 68 | } 69 | unsafe impl Sync for Index 70 | where 71 | K: Sync, 72 | V: Sync, 73 | { 74 | } 75 | 76 | #[derive(Debug)] 77 | #[repr(C)] 78 | struct Entry { 79 | key: K, 80 | val: V, 81 | next: u64, 82 | kv_checksum: u64, 83 | next_checksum: u64, 84 | } 85 | 86 | // Wrapper reference for mutating entries, carrying a mutex guard 87 | struct EntryMut<'a, K, V> { 88 | entry: &'a mut Entry, 89 | _lock: MutexGuard<'a, Shard>, 90 | } 91 | 92 | impl<'a, K, V> Deref for EntryMut<'a, K, V> { 93 | type Target = Entry; 94 | fn deref(&self) -> &Self::Target { 95 | &self.entry 96 | } 97 | } 98 | 99 | impl<'a, K, V> DerefMut for EntryMut<'a, K, V> { 100 | fn deref_mut(&mut self) -> &mut Self::Target { 101 | &mut self.entry 102 | } 103 | } 104 | 105 | impl Entry { 106 | fn new(key: K, val: V) -> Self { 107 | let kv_checksum = hash_val(&key).wrapping_add(hash_val(&val)); 108 | let entry = Entry { 109 | key, 110 | val, 111 | kv_checksum, 112 | next: 0, 113 | next_checksum: 0 + 1, 114 | }; 115 | debug_assert!(entry.valid()); 116 | entry 117 | } 118 | 119 | fn valid(&self) -> bool { 120 | if hash_val(&self.key).wrapping_add(hash_val(&self.val)) 121 | == self.kv_checksum 122 | && self.next + 1 == self.next_checksum 123 | { 124 | true 125 | } else { 126 | false 127 | } 128 | } 129 | 130 | fn set_next>(&mut self, next: I) { 131 | let next = next.into(); 132 | self.next = next; 133 | self.next_checksum = next + 1; 134 | } 135 | } 136 | 137 | impl Index 138 | where 139 | K: Pod + Hash + Copy + PartialEq, 140 | V: Pod + Hash + Copy, 141 | { 142 | /// Create or load an index at `path` 143 | pub fn new>(path: &P) -> io::Result { 144 | let mut lanes = ArrayVec::new(); 145 | 146 | // check for lane files already on disk 147 | for n in 0..NUM_LANES { 148 | let mut pathbuf = PathBuf::from(path.as_ref()); 149 | pathbuf.push(&format!("{:02x}", n)); 150 | 151 | if pathbuf.exists() { 152 | let file = 153 | OpenOptions::new().read(true).write(true).open(&pathbuf)?; 154 | 155 | let lane_pages = Self::lane_pages(n); 156 | let file_len = PAGE_SIZE as u64 * lane_pages as u64; 157 | file.set_len(file_len)?; 158 | unsafe { lanes.push(MmapMut::map_mut(&file)?) }; 159 | } 160 | } 161 | 162 | // find the number of already occupied pages 163 | let mut num_pages = 0; 164 | if let Some(last) = lanes.last() { 165 | // help the type inferance along a bit. 166 | let last: &MmapMut = last; 167 | 168 | // add up pages of all but the last lane, since they must all be full 169 | let mut full_pages = 0; 170 | for n in 0..lanes.len().saturating_sub(1) { 171 | full_pages += Self::lane_pages(n) 172 | } 173 | 174 | // do a binary search to find the last populated page in the last lane 175 | let mut low_bound = 0; 176 | let mut high_bound = Self::lane_pages(lanes.len() - 1) - 1; 177 | 178 | while low_bound + 1 != high_bound { 179 | let check = low_bound + (high_bound - low_bound) / 2; 180 | let page_ofs = PAGE_SIZE * check; 181 | 182 | // is there a valid entry in this page? 183 | for slot in 0..Self::entries_per_page() { 184 | let slot_ofs = 185 | page_ofs + slot * mem::size_of::>(); 186 | 187 | let ptr = last.as_ptr(); 188 | 189 | let entry: &Entry = unsafe { 190 | mem::transmute(ptr.offset(slot_ofs as isize)) 191 | }; 192 | 193 | if entry.valid() { 194 | low_bound = check; 195 | break; 196 | } 197 | } 198 | if low_bound != check { 199 | high_bound = check 200 | } 201 | } 202 | 203 | num_pages = full_pages + high_bound; 204 | } 205 | 206 | // create the index 207 | let index = Index { 208 | lanes: UnsafeCell::new(lanes), 209 | path: PathBuf::from(path.as_ref()), 210 | pages: Mutex::new(num_pages as u64), 211 | _marker: PhantomData, 212 | }; 213 | 214 | // initialize index with at least one page 215 | if num_pages == 0 { 216 | assert_eq!(index.new_page()?, 0); 217 | } 218 | Ok(index) 219 | } 220 | 221 | /// Returns how many pages have been allocated so far 222 | pub fn pages(&self) -> usize { 223 | *self.pages.lock() as usize 224 | } 225 | 226 | /// Returns how many pages fit into one lane 227 | #[inline(always)] 228 | fn lane_pages(n: usize) -> usize { 229 | 2_usize.pow(n as u32) * FIRST_LANE_PAGES 230 | } 231 | 232 | #[inline(always)] 233 | fn entries_per_page() -> usize { 234 | PAGE_SIZE / mem::size_of::>() 235 | } 236 | 237 | // calculates the slot in the page this hashed key would 238 | // occupy at a certain depth 239 | #[inline(always)] 240 | fn slot(key_hash: u64, depth: usize) -> usize { 241 | (hash_val(&(key_hash + depth as u64)) % Self::entries_per_page() as u64) 242 | as usize 243 | } 244 | 245 | // produces following output over page with FIRST_LANE_PAGES = 2 246 | // (0, 0), (0, 1), 247 | // (1, 0), (1, 1), (1, 2), (1, 3), 248 | // (2, 0), (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6), (2, 7), 249 | // ... and so on and so forth ... 250 | #[inline(always)] 251 | fn lane_page(page: usize) -> (usize, usize) { 252 | let usize_bits = mem::size_of::() * 8; 253 | let i = page / FIRST_LANE_PAGES + 1; 254 | let lane = usize_bits - i.leading_zeros() as usize - 1; 255 | let page = page - (2usize.pow(lane as u32) - 1) * FIRST_LANE_PAGES; 256 | (lane, page) 257 | } 258 | 259 | fn new_lane(&self) -> io::Result<()> { 260 | let lanes_ptr = self.lanes.get(); 261 | let lane_nr = unsafe { (*lanes_ptr).len() }; 262 | 263 | let num_pages = Self::lane_pages(lane_nr); 264 | 265 | let mut path = self.path.clone(); 266 | path.push(format!("{:02x}", lane_nr)); 267 | 268 | let file_len = PAGE_SIZE as u64 * num_pages as u64; 269 | 270 | let file = OpenOptions::new() 271 | .read(true) 272 | .write(true) 273 | .create(true) 274 | .open(&path)?; 275 | 276 | file.set_len(file_len)?; 277 | 278 | unsafe { (*lanes_ptr).push(MmapMut::map_mut(&file)?) } 279 | Ok(()) 280 | } 281 | 282 | fn new_page(&self) -> io::Result { 283 | let mut page_nr = self.pages.lock(); 284 | 285 | let (_, offset) = Self::lane_page(*page_nr as usize); 286 | 287 | if offset == 0 { 288 | // create new lane 289 | self.new_lane()? 290 | } 291 | 292 | let new_page_nr = *page_nr; 293 | *page_nr += 1; 294 | 295 | Ok(new_page_nr) 296 | } 297 | 298 | // Get a mutable reference to the `Entry`, 299 | fn entry(&self, lane: usize, page: usize, slot: usize) -> &Entry { 300 | // Get a reference to the `Entry` 301 | let page_ofs = PAGE_SIZE * page; 302 | let slot_ofs = page_ofs + slot * mem::size_of::>(); 303 | unsafe { 304 | mem::transmute( 305 | (*self.lanes.get())[lane].as_ptr().offset(slot_ofs as isize), 306 | ) 307 | } 308 | } 309 | 310 | // Get a mutable reference to the `Entry`, 311 | // locking the corresponding shard. 312 | fn entry_mut( 313 | &self, 314 | lane: usize, 315 | page: usize, 316 | slot: usize, 317 | ) -> EntryMut { 318 | let shard = (page ^ slot) % NUM_SHARDS; 319 | // Lock the entry for writing 320 | let lock = SHARDS[shard].lock(); 321 | 322 | let page_ofs = PAGE_SIZE * page; 323 | let slot_ofs = page_ofs + slot * mem::size_of::>(); 324 | EntryMut { 325 | entry: unsafe { 326 | mem::transmute( 327 | (*self.lanes.get())[lane] 328 | .as_ptr() 329 | .offset(slot_ofs as isize), 330 | ) 331 | }, 332 | _lock: lock, 333 | } 334 | } 335 | 336 | // Traverse the tree to find the entry for this key 337 | fn find_key(&self, k: &K) -> io::Result> { 338 | let mut depth = 0; 339 | let mut abs_page = 0; 340 | loop { 341 | let hash = hash_val(&k); 342 | let slot = Self::slot(hash, depth); 343 | 344 | let (lane, page) = Self::lane_page(abs_page); 345 | let entry = self.entry(lane, page, slot); 346 | 347 | if !entry.valid() { 348 | return Ok(Found::Invalid(lane, page, slot)); 349 | } 350 | 351 | if &entry.key == k { 352 | return Ok(Found::Some(entry)); 353 | } else if entry.next == 0 { 354 | return Ok(Found::None(lane, page, slot)); 355 | } else { 356 | abs_page = entry.next as usize; 357 | } 358 | 359 | depth += 1; 360 | } 361 | } 362 | 363 | /// Inserts a key-value pair into the index, if the key is already 364 | /// present, this is a no-op 365 | pub fn insert(&self, key: K, val: V) -> io::Result { 366 | match self.find_key(&key)? { 367 | Found::Some(_) => { 368 | // no-op 369 | Ok(true) 370 | } 371 | Found::Invalid(lane, page, slot) => { 372 | let mut entry = self.entry_mut(lane, page, slot); 373 | 374 | if entry.valid() && entry.next != 0 { 375 | // Someone already wrote here, recurse! 376 | // We accept the performance hit of re-traversing 377 | // the whole tree, since this case is uncommon, 378 | // and makes the implementation simpler. 379 | mem::drop(entry); 380 | self.insert(key, val) 381 | } else { 382 | *entry = Entry::new(key, val); 383 | return Ok(false); 384 | } 385 | } 386 | Found::None(lane, page, slot) => { 387 | let mut entry = self.entry_mut(lane, page, slot); 388 | if entry.next != 0 { 389 | // again, another thread was here before us 390 | } else { 391 | entry.set_next(self.new_page()?); 392 | } 393 | // recurse 394 | mem::drop(entry); 395 | self.insert(key, val) 396 | } 397 | } 398 | } 399 | 400 | /// Looks up a value with `key` in the index 401 | pub fn get(&self, key: &K) -> io::Result> { 402 | match self.find_key(key)? { 403 | Found::Some(entry) => Ok(Some(&entry.val)), 404 | _ => Ok(None), 405 | } 406 | } 407 | 408 | /// Syncronizes and flushes data to disk 409 | pub fn flush(&mut self) -> std::io::Result<()> { 410 | unsafe { 411 | let lanes = &mut *self.lanes.get(); 412 | for mmap in lanes { 413 | mmap.flush()?; 414 | } 415 | } 416 | Ok(()) 417 | } 418 | 419 | /// Get the approximate size on disk for the index 420 | pub fn on_disk_size(&self) -> usize { 421 | *self.pages.lock() as usize * PAGE_SIZE 422 | } 423 | } 424 | 425 | #[cfg(test)] 426 | mod tests { 427 | use std::sync::Arc; 428 | use std::thread; 429 | 430 | use rand::{seq::SliceRandom, thread_rng}; 431 | use tempfile::tempdir; 432 | 433 | use super::*; 434 | 435 | #[test] 436 | fn simple() { 437 | let dir = tempdir().unwrap(); 438 | let index = Index::new(&dir).unwrap(); 439 | index.insert(0, 0).unwrap(); 440 | assert_eq!(index.get(&0).unwrap(), Some(&0)); 441 | assert_eq!(index.on_disk_size(), PAGE_SIZE); 442 | } 443 | 444 | const N: u64 = 1024 * 256; 445 | 446 | #[test] 447 | fn multiple() { 448 | let dir = tempdir().unwrap(); 449 | let index = Index::new(&dir).unwrap(); 450 | for i in 0..N { 451 | index.insert(i, i).unwrap(); 452 | } 453 | for i in 0..N { 454 | assert_eq!(index.get(&i).unwrap(), Some(&i)); 455 | } 456 | } 457 | 458 | #[test] 459 | fn reload() { 460 | let dir = tempdir().unwrap(); 461 | let mut pages; 462 | { 463 | { 464 | let index_a = Index::new(&dir).unwrap(); 465 | for i in 0..N { 466 | index_a.insert(i, i).unwrap(); 467 | } 468 | pages = index_a.pages(); 469 | mem::drop(index_a); 470 | } 471 | 472 | let index_b = Index::new(&dir).unwrap(); 473 | 474 | // make sure the page count matches 475 | assert_eq!(pages, index_b.pages()); 476 | 477 | for i in 0..N { 478 | assert_eq!(index_b.get(&i).unwrap(), Some(&i)); 479 | } 480 | 481 | for i in N..N * 2 { 482 | index_b.insert(i, i).unwrap(); 483 | } 484 | pages = index_b.pages(); 485 | mem::drop(index_b); 486 | } 487 | 488 | let index_c = Index::new(&dir).unwrap(); 489 | 490 | // make sure the page count matches 491 | assert_eq!(pages, index_c.pages()); 492 | 493 | for i in 0..N * 2 { 494 | assert_eq!(index_c.get(&i).unwrap(), Some(&i)); 495 | } 496 | } 497 | 498 | const N_THREADS: usize = 8; 499 | 500 | // The stress test creates an index, and simultaneously writes 501 | // entries in random order from `N_THREADS` threads, 502 | // while at the same time reading from an equal amount of threads. 503 | // 504 | // When all threads are finished, a final read-through is made to see 505 | // that all key value pairs are present. 506 | #[test] 507 | fn stress() { 508 | let dir = tempdir().unwrap(); 509 | let index = Arc::new(Index::new(&dir).unwrap()); 510 | 511 | let mut all_indicies = vec![]; 512 | for i in 0..N { 513 | all_indicies.push(i); 514 | } 515 | 516 | let mut rng = thread_rng(); 517 | 518 | // shuffle the order of the writes 519 | let mut shuffles_write = vec![]; 520 | for _ in 0..N_THREADS { 521 | let mut new = all_indicies.clone(); 522 | SliceRandom::shuffle(&mut new[..], &mut rng); 523 | shuffles_write.push(new); 524 | } 525 | 526 | // shuffle the order of the reads 527 | let mut shuffles_read = vec![]; 528 | for _ in 0..N_THREADS { 529 | let mut new = all_indicies.clone(); 530 | SliceRandom::shuffle(&mut new[..], &mut rng); 531 | shuffles_read.push(new); 532 | } 533 | 534 | let mut threads_running = vec![]; 535 | 536 | for i in 0..N_THREADS { 537 | // shuffled write 538 | let shuffle_write = mem::replace(&mut shuffles_write[i], vec![]); 539 | let index_write = index.clone(); 540 | 541 | // shuffled reads 542 | let shuffle_read = mem::replace(&mut shuffles_read[i], vec![]); 543 | let index_read = index.clone(); 544 | 545 | // write threads 546 | threads_running.push(thread::spawn(move || { 547 | for write in shuffle_write { 548 | index_write.insert(write, write).unwrap(); 549 | } 550 | })); 551 | 552 | // read threads 553 | threads_running.push(thread::spawn(move || { 554 | for read in shuffle_read { 555 | match index_read.get(&read).unwrap() { 556 | Some(val) => assert_eq!(val, &read), 557 | None => (), 558 | } 559 | } 560 | })); 561 | } 562 | 563 | // make sure all threads finish successfully 564 | for thread in threads_running { 565 | thread.join().unwrap() 566 | } 567 | 568 | for i in 0..N { 569 | assert_eq!(index.get(&i).unwrap(), Some(&i)); 570 | } 571 | } 572 | } 573 | --------------------------------------------------------------------------------