Line data Source code
1 : //!
2 : //! Simple on-disk B-tree implementation
3 : //!
4 : //! This is used as the index structure within image and delta layers
5 : //!
6 : //! Features:
7 : //! - Fixed-width keys
8 : //! - Fixed-width values (VALUE_SZ)
9 : //! - The tree is created in a bulk operation. Insert/deletion after creation
10 : //! is not supported
11 : //! - page-oriented
12 : //!
13 : //! TODO:
14 : //! - maybe something like an Adaptive Radix Tree would be more efficient?
15 : //! - the values stored by image and delta layers are offsets into the file,
16 : //! and they are in monotonically increasing order. Prefix compression would
17 : //! be very useful for them, too.
18 : //! - An Iterator interface would be more convenient for the callers than the
19 : //! 'visit' function
20 : //!
21 : use std::cmp::Ordering;
22 : use std::iter::Rev;
23 : use std::ops::{Range, RangeInclusive};
24 : use std::{io, result};
25 :
26 : use async_stream::try_stream;
27 : use byteorder::{BE, ReadBytesExt};
28 : use bytes::{BufMut, Bytes, BytesMut};
29 : use either::Either;
30 : use futures::{Stream, StreamExt};
31 : use hex;
32 : use thiserror::Error;
33 : use tracing::error;
34 :
35 : use crate::context::RequestContext;
36 : use crate::tenant::block_io::{BlockReader, BlockWriter};
37 :
38 : // The maximum size of a value stored in the B-tree. 5 bytes is enough currently.
39 : pub const VALUE_SZ: usize = 5;
40 : pub const MAX_VALUE: u64 = 0x007f_ffff_ffff;
41 :
42 : pub const PAGE_SZ: usize = 8192;
43 :
44 : #[derive(Clone, Copy, Debug)]
45 : struct Value([u8; VALUE_SZ]);
46 :
47 : impl Value {
48 14122730 : fn from_slice(slice: &[u8]) -> Value {
49 14122730 : let mut b = [0u8; VALUE_SZ];
50 14122730 : b.copy_from_slice(slice);
51 14122730 : Value(b)
52 14122730 : }
53 :
54 14438465 : fn from_u64(x: u64) -> Value {
55 14438465 : assert!(x <= 0x007f_ffff_ffff);
56 14438465 : Value([
57 14438465 : (x >> 32) as u8,
58 14438465 : (x >> 24) as u8,
59 14438465 : (x >> 16) as u8,
60 14438465 : (x >> 8) as u8,
61 14438465 : x as u8,
62 14438465 : ])
63 14438465 : }
64 :
65 25782 : fn from_blknum(x: u32) -> Value {
66 25782 : Value([
67 25782 : 0x80,
68 25782 : (x >> 24) as u8,
69 25782 : (x >> 16) as u8,
70 25782 : (x >> 8) as u8,
71 25782 : x as u8,
72 25782 : ])
73 25782 : }
74 :
75 : #[allow(dead_code)]
76 0 : fn is_offset(self) -> bool {
77 0 : self.0[0] & 0x80 != 0
78 0 : }
79 :
80 12860871 : fn to_u64(self) -> u64 {
81 12860871 : let b = &self.0;
82 12860871 : ((b[0] as u64) << 32)
83 12860871 : | ((b[1] as u64) << 24)
84 12860871 : | ((b[2] as u64) << 16)
85 12860871 : | ((b[3] as u64) << 8)
86 12860871 : | b[4] as u64
87 12860871 : }
88 :
89 1249811 : fn to_blknum(self) -> u32 {
90 1249811 : let b = &self.0;
91 1249811 : assert!(b[0] == 0x80);
92 1249811 : ((b[1] as u32) << 24) | ((b[2] as u32) << 16) | ((b[3] as u32) << 8) | b[4] as u32
93 1249811 : }
94 : }
95 :
96 : #[derive(Error, Debug)]
97 : pub enum DiskBtreeError {
98 : #[error("Attempt to append a value that is too large {0} > {}", MAX_VALUE)]
99 : AppendOverflow(u64),
100 :
101 : #[error("Unsorted input: key {key:?} is <= last_key {last_key:?}")]
102 : UnsortedInput { key: Box<[u8]>, last_key: Box<[u8]> },
103 :
104 : #[error("Could not push to new leaf node")]
105 : FailedToPushToNewLeafNode,
106 :
107 : #[error("IoError: {0}")]
108 : Io(#[from] io::Error),
109 : }
110 :
111 : pub type Result<T> = result::Result<T, DiskBtreeError>;
112 :
113 : /// This is the on-disk representation.
114 : struct OnDiskNode<'a, const L: usize> {
115 : // Fixed-width fields
116 : num_children: u16,
117 : level: u8,
118 : prefix_len: u8,
119 : suffix_len: u8,
120 :
121 : // Variable-length fields. These are stored on-disk after the fixed-width
122 : // fields, in this order. In the in-memory representation, these point to
123 : // the right parts in the page buffer.
124 : prefix: &'a [u8],
125 : keys: &'a [u8],
126 : values: &'a [u8],
127 : }
128 :
129 : impl<const L: usize> OnDiskNode<'_, L> {
130 : ///
131 : /// Interpret a PAGE_SZ page as a node.
132 : ///
133 3001994 : fn deparse(buf: &[u8]) -> Result<OnDiskNode<L>> {
134 3001994 : let mut cursor = std::io::Cursor::new(buf);
135 3001994 : let num_children = cursor.read_u16::<BE>()?;
136 3001994 : let level = cursor.read_u8()?;
137 3001994 : let prefix_len = cursor.read_u8()?;
138 3001994 : let suffix_len = cursor.read_u8()?;
139 :
140 3001994 : let mut off = cursor.position();
141 3001994 : let prefix_off = off as usize;
142 3001994 : off += prefix_len as u64;
143 3001994 :
144 3001994 : let keys_off = off as usize;
145 3001994 : let keys_len = num_children as usize * suffix_len as usize;
146 3001994 : off += keys_len as u64;
147 3001994 :
148 3001994 : let values_off = off as usize;
149 3001994 : let values_len = num_children as usize * VALUE_SZ;
150 3001994 : //off += values_len as u64;
151 3001994 :
152 3001994 : let prefix = &buf[prefix_off..prefix_off + prefix_len as usize];
153 3001994 : let keys = &buf[keys_off..keys_off + keys_len];
154 3001994 : let values = &buf[values_off..values_off + values_len];
155 3001994 :
156 3001994 : Ok(OnDiskNode {
157 3001994 : num_children,
158 3001994 : level,
159 3001994 : prefix_len,
160 3001994 : suffix_len,
161 3001994 : prefix,
162 3001994 : keys,
163 3001994 : values,
164 3001994 : })
165 3001994 : }
166 :
167 : ///
168 : /// Read a value at 'idx'
169 : ///
170 14122730 : fn value(&self, idx: usize) -> Value {
171 14122730 : let value_off = idx * VALUE_SZ;
172 14122730 : let value_slice = &self.values[value_off..value_off + VALUE_SZ];
173 14122730 : Value::from_slice(value_slice)
174 14122730 : }
175 :
176 2554303 : fn binary_search(
177 2554303 : &self,
178 2554303 : search_key: &[u8; L],
179 2554303 : keybuf: &mut [u8],
180 2554303 : ) -> result::Result<usize, usize> {
181 2554303 : let mut size = self.num_children as usize;
182 2554303 : let mut low = 0;
183 2554303 : let mut high = size;
184 19521482 : while low < high {
185 17423904 : let mid = low + size / 2;
186 17423904 :
187 17423904 : let key_off = mid * self.suffix_len as usize;
188 17423904 : let suffix = &self.keys[key_off..key_off + self.suffix_len as usize];
189 17423904 : // Does this match?
190 17423904 : keybuf[self.prefix_len as usize..].copy_from_slice(suffix);
191 17423904 :
192 17423904 : let cmp = keybuf[..].cmp(search_key);
193 17423904 :
194 17423904 : if cmp == Ordering::Less {
195 11147015 : low = mid + 1;
196 11147015 : } else if cmp == Ordering::Greater {
197 5820164 : high = mid;
198 5820164 : } else {
199 456725 : return Ok(mid);
200 : }
201 16967179 : size = high - low;
202 : }
203 2097578 : Err(low)
204 2554303 : }
205 : }
206 :
207 : ///
208 : /// Public reader object, to search the tree.
209 : ///
210 : #[derive(Clone)]
211 : pub struct DiskBtreeReader<R, const L: usize>
212 : where
213 : R: BlockReader,
214 : {
215 : start_blk: u32,
216 : root_blk: u32,
217 : reader: R,
218 : }
219 :
220 : #[derive(Clone, Copy, Debug, PartialEq, Eq)]
221 : pub enum VisitDirection {
222 : Forwards,
223 : Backwards,
224 : }
225 :
226 : impl<R, const L: usize> DiskBtreeReader<R, L>
227 : where
228 : R: BlockReader,
229 : {
230 481603 : pub fn new(start_blk: u32, root_blk: u32, reader: R) -> Self {
231 481603 : DiskBtreeReader {
232 481603 : start_blk,
233 481603 : root_blk,
234 481603 : reader,
235 481603 : }
236 481603 : }
237 :
238 : ///
239 : /// Read the value for given key. Returns the value, or None if it doesn't exist.
240 : ///
241 806329 : pub async fn get(&self, search_key: &[u8; L], ctx: &RequestContext) -> Result<Option<u64>> {
242 806329 : let mut result: Option<u64> = None;
243 806329 : self.visit(
244 806329 : search_key,
245 806329 : VisitDirection::Forwards,
246 806329 : |key, value| {
247 406281 : if key == search_key {
248 402269 : result = Some(value);
249 402269 : }
250 406281 : false
251 806329 : },
252 806329 : ctx,
253 806329 : )
254 806329 : .await?;
255 806329 : Ok(result)
256 806329 : }
257 :
258 1396 : pub fn iter<'a>(self, start_key: &'a [u8; L], ctx: &'a RequestContext) -> DiskBtreeIterator<'a>
259 1396 : where
260 1396 : R: 'a + Send,
261 1396 : {
262 1396 : DiskBtreeIterator {
263 1396 : stream: Box::pin(self.into_stream(start_key, ctx)),
264 1396 : }
265 1396 : }
266 :
267 : /// Return a stream which yields all key, value pairs from the index
268 : /// starting from the first key greater or equal to `start_key`.
269 : ///
270 : /// Note 1: that this is a copy of [`Self::visit`].
271 : /// TODO: Once the sequential read path is removed this will become
272 : /// the only index traversal method.
273 : ///
274 : /// Note 2: this function used to take `&self` but it now consumes `self`. This is due to
275 : /// the lifetime constraints of the reader and the stream / iterator it creates. Using `&self`
276 : /// requires the reader to be present when the stream is used, and this creates a lifetime
277 : /// dependency between the reader and the stream. Now if we want to create an iterator that
278 : /// holds the stream, someone will need to keep a reference to the reader, which is inconvenient
279 : /// to use from the image/delta layer APIs.
280 : ///
281 : /// Feel free to add the `&self` variant back if it's necessary.
282 481259 : pub fn into_stream<'a>(
283 481259 : self,
284 481259 : start_key: &'a [u8; L],
285 481259 : ctx: &'a RequestContext,
286 481259 : ) -> impl Stream<Item = std::result::Result<(Vec<u8>, u64), DiskBtreeError>> + 'a
287 481259 : where
288 481259 : R: 'a,
289 481259 : {
290 481259 : try_stream! {
291 481259 : let mut stack = Vec::new();
292 481259 : stack.push((self.root_blk, None));
293 481259 : let block_cursor = self.reader.block_cursor();
294 481259 : let mut node_buf = [0_u8; PAGE_SZ];
295 481259 : while let Some((node_blknum, opt_iter)) = stack.pop() {
296 481259 : // Read the node, through the PS PageCache, into local variable `node_buf`.
297 481259 : // We could keep the page cache read guard alive, but, at the time of writing,
298 481259 : // we run quite small PS PageCache s => can't risk running out of
299 481259 : // PageCache space because this stream isn't consumed fast enough.
300 481259 : let page_read_guard = block_cursor
301 481259 : .read_blk(self.start_blk + node_blknum, ctx)
302 481259 : .await?;
303 481259 : node_buf.copy_from_slice(page_read_guard.as_ref());
304 481259 : drop(page_read_guard); // drop page cache read guard early
305 481259 :
306 481259 : let node = OnDiskNode::deparse(&node_buf)?;
307 481259 : let prefix_len = node.prefix_len as usize;
308 481259 : let suffix_len = node.suffix_len as usize;
309 481259 :
310 481259 : assert!(node.num_children > 0);
311 481259 :
312 481259 : let mut keybuf = Vec::new();
313 481259 : keybuf.extend(node.prefix);
314 481259 : keybuf.resize(prefix_len + suffix_len, 0);
315 481259 :
316 481259 : let mut iter: Either<Range<usize>, Rev<RangeInclusive<usize>>> = if let Some(iter) = opt_iter {
317 481259 : iter
318 481259 : } else {
319 481259 : // Locate the first match
320 481259 : let idx = match node.binary_search(start_key, keybuf.as_mut_slice()) {
321 481259 : Ok(idx) => idx,
322 481259 : Err(idx) => {
323 481259 : if node.level == 0 {
324 481259 : // Imagine that the node contains the following keys:
325 481259 : //
326 481259 : // 1
327 481259 : // 3 <-- idx
328 481259 : // 5
329 481259 : //
330 481259 : // If the search key is '2' and there is exact match,
331 481259 : // the binary search would return the index of key
332 481259 : // '3'. That's cool, '3' is the first key to return.
333 481259 : idx
334 481259 : } else {
335 481259 : // This is an internal page, so each key represents a lower
336 481259 : // bound for what's in the child page. If there is no exact
337 481259 : // match, we have to return the *previous* entry.
338 481259 : //
339 481259 : // 1 <-- return this
340 481259 : // 3 <-- idx
341 481259 : // 5
342 481259 : idx.saturating_sub(1)
343 481259 : }
344 481259 : }
345 481259 : };
346 481259 : Either::Left(idx..node.num_children.into())
347 481259 : };
348 481259 :
349 481259 :
350 481259 : // idx points to the first match now. Keep going from there
351 481259 : while let Some(idx) = iter.next() {
352 481259 : let key_off = idx * suffix_len;
353 481259 : let suffix = &node.keys[key_off..key_off + suffix_len];
354 481259 : keybuf[prefix_len..].copy_from_slice(suffix);
355 481259 : let value = node.value(idx);
356 481259 : #[allow(clippy::collapsible_if)]
357 481259 : if node.level == 0 {
358 481259 : // leaf
359 481259 : yield (keybuf.clone(), value.to_u64());
360 481259 : } else {
361 481259 : stack.push((node_blknum, Some(iter)));
362 481259 : stack.push((value.to_blknum(), None));
363 481259 : break;
364 481259 : }
365 481259 : }
366 481259 : }
367 481259 : }
368 481259 : }
369 :
370 : ///
371 : /// Scan the tree, starting from 'search_key', in the given direction. 'visitor'
372 : /// will be called for every key >= 'search_key' (or <= 'search_key', if scanning
373 : /// backwards)
374 : ///
375 823249 : pub async fn visit<V>(
376 823249 : &self,
377 823249 : search_key: &[u8; L],
378 823249 : dir: VisitDirection,
379 823249 : mut visitor: V,
380 823249 : ctx: &RequestContext,
381 823249 : ) -> Result<bool>
382 823249 : where
383 823249 : V: FnMut(&[u8], u64) -> bool,
384 823249 : {
385 823249 : let mut stack = Vec::new();
386 823249 : stack.push((self.root_blk, None));
387 823249 : let block_cursor = self.reader.block_cursor();
388 2438150 : while let Some((node_blknum, opt_iter)) = stack.pop() {
389 : // Locate the node.
390 2037082 : let node_buf = block_cursor
391 2037082 : .read_blk(self.start_blk + node_blknum, ctx)
392 2037082 : .await?;
393 :
394 2037082 : let node = OnDiskNode::deparse(node_buf.as_ref())?;
395 2037082 : let prefix_len = node.prefix_len as usize;
396 2037082 : let suffix_len = node.suffix_len as usize;
397 2037082 :
398 2037082 : assert!(node.num_children > 0);
399 :
400 2037082 : let mut keybuf = Vec::new();
401 2037082 : keybuf.extend(node.prefix);
402 2037082 : keybuf.resize(prefix_len + suffix_len, 0);
403 :
404 2037082 : let mut iter = if let Some(iter) = opt_iter {
405 407796 : iter
406 1629286 : } else if dir == VisitDirection::Forwards {
407 : // Locate the first match
408 1621234 : let idx = match node.binary_search(search_key, keybuf.as_mut_slice()) {
409 406685 : Ok(idx) => idx,
410 1214549 : Err(idx) => {
411 1214549 : if node.level == 0 {
412 : // Imagine that the node contains the following keys:
413 : //
414 : // 1
415 : // 3 <-- idx
416 : // 5
417 : //
418 : // If the search key is '2' and there is exact match,
419 : // the binary search would return the index of key
420 : // '3'. That's cool, '3' is the first key to return.
421 416232 : idx
422 : } else {
423 : // This is an internal page, so each key represents a lower
424 : // bound for what's in the child page. If there is no exact
425 : // match, we have to return the *previous* entry.
426 : //
427 : // 1 <-- return this
428 : // 3 <-- idx
429 : // 5
430 798317 : idx.saturating_sub(1)
431 : }
432 : }
433 : };
434 1621234 : Either::Left(idx..node.num_children.into())
435 : } else {
436 8052 : let idx = match node.binary_search(search_key, keybuf.as_mut_slice()) {
437 4004 : Ok(idx) => {
438 4004 : // Exact match. That's the first entry to return, and walk
439 4004 : // backwards from there.
440 4004 : idx
441 : }
442 4048 : Err(idx) => {
443 : // No exact match. The binary search returned the index of the
444 : // first key that's > search_key. Back off by one, and walk
445 : // backwards from there.
446 4048 : if let Some(idx) = idx.checked_sub(1) {
447 4040 : idx
448 : } else {
449 8 : return Ok(false);
450 : }
451 : }
452 : };
453 8044 : Either::Right((0..=idx).rev())
454 : };
455 :
456 : // idx points to the first match now. Keep going from there
457 6324982 : while let Some(idx) = iter.next() {
458 5516118 : let key_off = idx * suffix_len;
459 5516118 : let suffix = &node.keys[key_off..key_off + suffix_len];
460 5516118 : keybuf[prefix_len..].copy_from_slice(suffix);
461 5516118 : let value = node.value(idx);
462 5516118 : #[allow(clippy::collapsible_if)]
463 5516118 : if node.level == 0 {
464 : // leaf
465 4710081 : if !visitor(&keybuf, value.to_u64()) {
466 422173 : return Ok(false);
467 4287908 : }
468 : } else {
469 806037 : stack.push((node_blknum, Some(iter)));
470 806037 : stack.push((value.to_blknum(), None));
471 806037 : break;
472 : }
473 : }
474 : }
475 401068 : Ok(true)
476 823249 : }
477 :
478 : #[allow(dead_code)]
479 20 : pub async fn dump(&self, ctx: &RequestContext) -> Result<()> {
480 20 : let mut stack = Vec::new();
481 20 :
482 20 : stack.push((self.root_blk, String::new(), 0, 0, 0));
483 20 :
484 20 : let block_cursor = self.reader.block_cursor();
485 :
486 12084 : while let Some((blknum, path, depth, child_idx, key_off)) = stack.pop() {
487 12064 : let blk = block_cursor.read_blk(self.start_blk + blknum, ctx).await?;
488 12064 : let buf: &[u8] = blk.as_ref();
489 12064 : let node = OnDiskNode::<L>::deparse(buf)?;
490 :
491 12064 : if child_idx == 0 {
492 36 : print!("{:indent$}", "", indent = depth * 2);
493 36 : let path_prefix = stack
494 36 : .iter()
495 36 : .map(|(_blknum, path, ..)| path.as_str())
496 36 : .collect::<String>();
497 36 : println!(
498 36 : "blk #{blknum}: path {path_prefix}{path}: prefix {}, suffix_len {}",
499 36 : hex::encode(node.prefix),
500 36 : node.suffix_len
501 36 : );
502 12028 : }
503 :
504 12064 : if child_idx + 1 < node.num_children {
505 12028 : let key_off = key_off + node.suffix_len as usize;
506 12028 : stack.push((blknum, path.clone(), depth, child_idx + 1, key_off));
507 12028 : }
508 12064 : let key = &node.keys[key_off..key_off + node.suffix_len as usize];
509 12064 : let val = node.value(child_idx as usize);
510 12064 :
511 12064 : print!("{:indent$}", "", indent = depth * 2 + 2);
512 12064 : println!("{}: {}", hex::encode(key), hex::encode(val.0));
513 12064 :
514 12064 : if node.level > 0 {
515 16 : stack.push((val.to_blknum(), hex::encode(node.prefix), depth + 1, 0, 0));
516 12048 : }
517 : }
518 20 : Ok(())
519 20 : }
520 : }
521 :
522 : pub struct DiskBtreeIterator<'a> {
523 : #[allow(clippy::type_complexity)]
524 : stream: std::pin::Pin<
525 : Box<dyn Stream<Item = std::result::Result<(Vec<u8>, u64), DiskBtreeError>> + 'a + Send>,
526 : >,
527 : }
528 :
529 : impl DiskBtreeIterator<'_> {
530 4647557 : pub async fn next(&mut self) -> Option<std::result::Result<(Vec<u8>, u64), DiskBtreeError>> {
531 4647557 : self.stream.next().await
532 4647557 : }
533 : }
534 :
535 : ///
536 : /// Public builder object, for creating a new tree.
537 : ///
538 : /// Usage: Create a builder object by calling 'new', load all the data into the
539 : /// tree by calling 'append' for each key-value pair, and then call 'finish'
540 : ///
541 : /// 'L' is the key length in bytes
542 : pub struct DiskBtreeBuilder<W, const L: usize>
543 : where
544 : W: BlockWriter,
545 : {
546 : writer: W,
547 :
548 : ///
549 : /// `stack[0]` is the current root page, `stack.last()` is the leaf.
550 : ///
551 : /// We maintain the length of the stack to be always greater than zero.
552 : /// Two exceptions are:
553 : /// 1. `Self::flush_node`. The method will push the new node if it extracted the last one.
554 : /// So because other methods cannot see the intermediate state invariant still holds.
555 : /// 2. `Self::finish`. It consumes self and does not return it back,
556 : /// which means that this is where the structure is destroyed.
557 : /// Thus stack of zero length cannot be observed by other methods.
558 : stack: Vec<BuildNode<L>>,
559 :
560 : /// Last key that was appended to the tree. Used to sanity check that append
561 : /// is called in increasing key order.
562 : last_key: Option<[u8; L]>,
563 : }
564 :
565 : impl<W, const L: usize> DiskBtreeBuilder<W, L>
566 : where
567 : W: BlockWriter,
568 : {
569 4164 : pub fn new(writer: W) -> Self {
570 4164 : DiskBtreeBuilder {
571 4164 : writer,
572 4164 : last_key: None,
573 4164 : stack: vec![BuildNode::new(0)],
574 4164 : }
575 4164 : }
576 :
577 14438469 : pub fn append(&mut self, key: &[u8; L], value: u64) -> Result<()> {
578 14438469 : if value > MAX_VALUE {
579 0 : return Err(DiskBtreeError::AppendOverflow(value));
580 14438469 : }
581 14438469 : if let Some(last_key) = &self.last_key {
582 14434737 : if key <= last_key {
583 4 : return Err(DiskBtreeError::UnsortedInput {
584 4 : key: key.as_slice().into(),
585 4 : last_key: last_key.as_slice().into(),
586 4 : });
587 14434733 : }
588 3732 : }
589 14438465 : self.last_key = Some(*key);
590 14438465 :
591 14438465 : self.append_internal(key, Value::from_u64(value))
592 14438469 : }
593 :
594 14464247 : fn append_internal(&mut self, key: &[u8; L], value: Value) -> Result<()> {
595 14464247 : // Try to append to the current leaf buffer
596 14464247 : let last = self
597 14464247 : .stack
598 14464247 : .last_mut()
599 14464247 : .expect("should always have at least one item");
600 14464247 : let level = last.level;
601 14464247 : if last.push(key, value) {
602 14415200 : return Ok(());
603 49047 : }
604 49047 :
605 49047 : // It did not fit. Try to compress, and if it succeeds to make
606 49047 : // some room on the node, try appending to it again.
607 49047 : #[allow(clippy::collapsible_if)]
608 49047 : if last.compress() {
609 24872 : if last.push(key, value) {
610 24861 : return Ok(());
611 11 : }
612 24175 : }
613 :
614 : // Could not append to the current leaf. Flush it and create a new one.
615 24186 : self.flush_node()?;
616 :
617 : // Replace the node we flushed with an empty one and append the new
618 : // key to it.
619 24186 : let mut last = BuildNode::new(level);
620 24186 : if !last.push(key, value) {
621 0 : return Err(DiskBtreeError::FailedToPushToNewLeafNode);
622 24186 : }
623 24186 :
624 24186 : self.stack.push(last);
625 24186 :
626 24186 : Ok(())
627 14464247 : }
628 :
629 : /// Flush the bottommost node in the stack to disk. Appends a downlink to its parent,
630 : /// and recursively flushes the parent too, if it becomes full. If the root page becomes full,
631 : /// creates a new root page, increasing the height of the tree.
632 25782 : fn flush_node(&mut self) -> Result<()> {
633 25782 : // Get the current bottommost node in the stack and flush it to disk.
634 25782 : let last = self
635 25782 : .stack
636 25782 : .pop()
637 25782 : .expect("should always have at least one item");
638 25782 : let buf = last.pack();
639 25782 : let downlink_key = last.first_key();
640 25782 : let downlink_ptr = self.writer.write_blk(buf)?;
641 :
642 : // Append the downlink to the parent. If there is no parent, ie. this was the root page,
643 : // create a new root page, increasing the height of the tree.
644 25782 : if self.stack.is_empty() {
645 1596 : self.stack.push(BuildNode::new(last.level + 1));
646 24186 : }
647 25782 : self.append_internal(&downlink_key, Value::from_blknum(downlink_ptr))
648 25782 : }
649 :
650 : ///
651 : /// Flushes everything to disk, and returns the block number of the root page.
652 : /// The caller must store the root block number "out-of-band", and pass it
653 : /// to the DiskBtreeReader::new() when you want to read the tree again.
654 : /// (In the image and delta layers, it is stored in the beginning of the file,
655 : /// in the summary header)
656 : ///
657 3636 : pub fn finish(mut self) -> Result<(u32, W)> {
658 : // flush all levels, except the root.
659 5232 : while self.stack.len() > 1 {
660 1596 : self.flush_node()?;
661 : }
662 :
663 3636 : let root = self
664 3636 : .stack
665 3636 : .first()
666 3636 : .expect("by the check above we left one item there");
667 3636 : let buf = root.pack();
668 3636 : let root_blknum = self.writer.write_blk(buf)?;
669 :
670 3636 : Ok((root_blknum, self.writer))
671 3636 : }
672 :
673 4095304 : pub fn borrow_writer(&self) -> &W {
674 4095304 : &self.writer
675 4095304 : }
676 : }
677 :
678 : ///
679 : /// BuildNode represesnts an incomplete page that we are appending to.
680 : ///
681 : #[derive(Clone, Debug)]
682 : struct BuildNode<const L: usize> {
683 : num_children: u16,
684 : level: u8,
685 : prefix: Vec<u8>,
686 : suffix_len: usize,
687 :
688 : keys: Vec<u8>,
689 : values: Vec<u8>,
690 :
691 : size: usize, // physical size of this node, if it was written to disk like this
692 : }
693 :
694 : const NODE_SIZE: usize = PAGE_SZ;
695 :
696 : const NODE_HDR_SIZE: usize = 2 + 1 + 1 + 1;
697 :
698 : impl<const L: usize> BuildNode<L> {
699 29946 : fn new(level: u8) -> Self {
700 29946 : BuildNode {
701 29946 : num_children: 0,
702 29946 : level,
703 29946 : prefix: Vec::new(),
704 29946 : suffix_len: 0,
705 29946 : keys: Vec::new(),
706 29946 : values: Vec::new(),
707 29946 : size: NODE_HDR_SIZE,
708 29946 : }
709 29946 : }
710 :
711 : /// Try to append a key-value pair to this node. Returns 'true' on
712 : /// success, 'false' if the page was full or the key was
713 : /// incompatible with the prefix of the existing keys.
714 14513305 : fn push(&mut self, key: &[u8; L], value: Value) -> bool {
715 14513305 : // If we have already performed prefix-compression on the page,
716 14513305 : // check that the incoming key has the same prefix.
717 14513305 : if self.num_children > 0 {
718 : // does the prefix allow it?
719 14483791 : if !key.starts_with(&self.prefix) {
720 457 : return false;
721 14483334 : }
722 29514 : } else {
723 29514 : self.suffix_len = key.len();
724 29514 : }
725 :
726 : // Is the node too full?
727 14512848 : if self.size + self.suffix_len + VALUE_SZ >= NODE_SIZE {
728 48601 : return false;
729 14464247 : }
730 14464247 :
731 14464247 : // All clear
732 14464247 : self.num_children += 1;
733 14464247 : self.keys.extend(&key[self.prefix.len()..]);
734 14464247 : self.values.extend(value.0);
735 14464247 :
736 14464247 : assert!(self.keys.len() == self.num_children as usize * self.suffix_len);
737 14464247 : assert!(self.values.len() == self.num_children as usize * VALUE_SZ);
738 :
739 14464247 : self.size += self.suffix_len + VALUE_SZ;
740 14464247 :
741 14464247 : true
742 14513305 : }
743 :
744 : ///
745 : /// Perform prefix-compression.
746 : ///
747 : /// Returns 'true' on success, 'false' if no compression was possible.
748 : ///
749 49047 : fn compress(&mut self) -> bool {
750 49047 : let first_suffix = self.first_suffix();
751 49047 : let last_suffix = self.last_suffix();
752 49047 :
753 49047 : // Find the common prefix among all keys
754 49047 : let mut prefix_len = 0;
755 445759 : while prefix_len < self.suffix_len {
756 445759 : if first_suffix[prefix_len] != last_suffix[prefix_len] {
757 49047 : break;
758 396712 : }
759 396712 : prefix_len += 1;
760 : }
761 49047 : if prefix_len == 0 {
762 24175 : return false;
763 24872 : }
764 24872 :
765 24872 : // Can compress. Rewrite the keys without the common prefix.
766 24872 : self.prefix.extend(&self.keys[..prefix_len]);
767 24872 :
768 24872 : let mut new_keys = Vec::new();
769 24872 : let mut key_off = 0;
770 6728911 : while key_off < self.keys.len() {
771 6704039 : let next_key_off = key_off + self.suffix_len;
772 6704039 : new_keys.extend(&self.keys[key_off + prefix_len..next_key_off]);
773 6704039 : key_off = next_key_off;
774 6704039 : }
775 24872 : self.keys = new_keys;
776 24872 : self.suffix_len -= prefix_len;
777 24872 :
778 24872 : self.size -= prefix_len * self.num_children as usize;
779 24872 : self.size += prefix_len;
780 24872 :
781 24872 : assert!(self.keys.len() == self.num_children as usize * self.suffix_len);
782 24872 : assert!(self.values.len() == self.num_children as usize * VALUE_SZ);
783 :
784 24872 : true
785 49047 : }
786 :
787 : ///
788 : /// Serialize the node to on-disk format.
789 : ///
790 29418 : fn pack(&self) -> Bytes {
791 29418 : assert!(self.keys.len() == self.num_children as usize * self.suffix_len);
792 29418 : assert!(self.values.len() == self.num_children as usize * VALUE_SZ);
793 29418 : assert!(self.num_children > 0);
794 :
795 29418 : let mut buf = BytesMut::new();
796 29418 :
797 29418 : buf.put_u16(self.num_children);
798 29418 : buf.put_u8(self.level);
799 29418 : buf.put_u8(self.prefix.len() as u8);
800 29418 : buf.put_u8(self.suffix_len as u8);
801 29418 : buf.put(&self.prefix[..]);
802 29418 : buf.put(&self.keys[..]);
803 29418 : buf.put(&self.values[..]);
804 29418 :
805 29418 : assert!(buf.len() == self.size);
806 :
807 29418 : assert!(buf.len() <= PAGE_SZ);
808 29418 : buf.resize(PAGE_SZ, 0);
809 29418 : buf.freeze()
810 29418 : }
811 :
812 74829 : fn first_suffix(&self) -> &[u8] {
813 74829 : &self.keys[..self.suffix_len]
814 74829 : }
815 49047 : fn last_suffix(&self) -> &[u8] {
816 49047 : &self.keys[self.keys.len() - self.suffix_len..]
817 49047 : }
818 :
819 : /// Return the full first key of the page, including the prefix
820 25782 : fn first_key(&self) -> [u8; L] {
821 25782 : let mut key = [0u8; L];
822 25782 : key[..self.prefix.len()].copy_from_slice(&self.prefix);
823 25782 : key[self.prefix.len()..].copy_from_slice(self.first_suffix());
824 25782 : key
825 25782 : }
826 : }
827 :
828 : #[cfg(test)]
829 : pub(crate) mod tests {
830 : use std::collections::BTreeMap;
831 : use std::sync::atomic::{AtomicUsize, Ordering};
832 :
833 : use rand::Rng;
834 :
835 : use super::*;
836 : use crate::context::DownloadBehavior;
837 : use crate::task_mgr::TaskKind;
838 : use crate::tenant::block_io::{BlockCursor, BlockLease, BlockReaderRef};
839 :
840 : #[derive(Clone, Default)]
841 : pub(crate) struct TestDisk {
842 : blocks: Vec<Bytes>,
843 : }
844 : impl TestDisk {
845 20 : fn new() -> Self {
846 20 : Self::default()
847 20 : }
848 2033570 : pub(crate) fn read_blk(&self, blknum: u32) -> io::Result<BlockLease> {
849 2033570 : let mut buf = [0u8; PAGE_SZ];
850 2033570 : buf.copy_from_slice(&self.blocks[blknum as usize]);
851 2033570 : Ok(std::sync::Arc::new(buf).into())
852 2033570 : }
853 : }
854 : impl BlockReader for TestDisk {
855 822461 : fn block_cursor(&self) -> BlockCursor<'_> {
856 822461 : BlockCursor::new(BlockReaderRef::TestDisk(self))
857 822461 : }
858 : }
859 : impl BlockWriter for &mut TestDisk {
860 432 : fn write_blk(&mut self, buf: Bytes) -> io::Result<u32> {
861 432 : let blknum = self.blocks.len();
862 432 : self.blocks.push(buf);
863 432 : Ok(blknum as u32)
864 432 : }
865 : }
866 :
867 : #[tokio::test]
868 4 : async fn basic() -> Result<()> {
869 4 : let mut disk = TestDisk::new();
870 4 : let mut writer = DiskBtreeBuilder::<_, 6>::new(&mut disk);
871 4 :
872 4 : let ctx =
873 4 : RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error).with_scope_unit_test();
874 4 :
875 4 : let all_keys: Vec<&[u8; 6]> = vec![
876 4 : b"xaaaaa", b"xaaaba", b"xaaaca", b"xabaaa", b"xababa", b"xabaca", b"xabada", b"xabadb",
877 4 : ];
878 4 : let all_data: Vec<(&[u8; 6], u64)> = all_keys
879 4 : .iter()
880 4 : .enumerate()
881 32 : .map(|(idx, key)| (*key, idx as u64))
882 4 : .collect();
883 32 : for (key, val) in all_data.iter() {
884 32 : writer.append(key, *val)?;
885 4 : }
886 4 :
887 4 : let (root_offset, _writer) = writer.finish()?;
888 4 :
889 4 : let reader = DiskBtreeReader::new(0, root_offset, disk);
890 4 :
891 4 : reader.dump(&ctx).await?;
892 4 :
893 4 : // Test the `get` function on all the keys.
894 32 : for (key, val) in all_data.iter() {
895 32 : assert_eq!(reader.get(key, &ctx).await?, Some(*val));
896 4 : }
897 4 : // And on some keys that don't exist
898 4 : assert_eq!(reader.get(b"aaaaaa", &ctx).await?, None);
899 4 : assert_eq!(reader.get(b"zzzzzz", &ctx).await?, None);
900 4 : assert_eq!(reader.get(b"xaaabx", &ctx).await?, None);
901 4 :
902 4 : // Test search with `visit` function
903 4 : let search_key = b"xabaaa";
904 4 : let expected: Vec<(Vec<u8>, u64)> = all_data
905 4 : .iter()
906 32 : .filter(|(key, _value)| key[..] >= search_key[..])
907 20 : .map(|(key, value)| (key.to_vec(), *value))
908 4 : .collect();
909 4 :
910 4 : let mut data = Vec::new();
911 4 : reader
912 4 : .visit(
913 4 : search_key,
914 4 : VisitDirection::Forwards,
915 20 : |key, value| {
916 20 : data.push((key.to_vec(), value));
917 20 : true
918 20 : },
919 4 : &ctx,
920 4 : )
921 4 : .await?;
922 4 : assert_eq!(data, expected);
923 4 :
924 4 : // Test a backwards scan
925 4 : let mut expected: Vec<(Vec<u8>, u64)> = all_data
926 4 : .iter()
927 32 : .filter(|(key, _value)| key[..] <= search_key[..])
928 16 : .map(|(key, value)| (key.to_vec(), *value))
929 4 : .collect();
930 4 : expected.reverse();
931 4 : let mut data = Vec::new();
932 4 : reader
933 4 : .visit(
934 4 : search_key,
935 4 : VisitDirection::Backwards,
936 16 : |key, value| {
937 16 : data.push((key.to_vec(), value));
938 16 : true
939 16 : },
940 4 : &ctx,
941 4 : )
942 4 : .await?;
943 4 : assert_eq!(data, expected);
944 4 :
945 4 : // Backward scan where nothing matches
946 4 : reader
947 4 : .visit(
948 4 : b"aaaaaa",
949 4 : VisitDirection::Backwards,
950 4 : |key, value| {
951 0 : panic!("found unexpected key {}: {}", hex::encode(key), value);
952 4 : },
953 4 : &ctx,
954 4 : )
955 4 : .await?;
956 4 :
957 4 : // Full scan
958 4 : let expected: Vec<(Vec<u8>, u64)> = all_data
959 4 : .iter()
960 32 : .map(|(key, value)| (key.to_vec(), *value))
961 4 : .collect();
962 4 : let mut data = Vec::new();
963 4 : reader
964 4 : .visit(
965 4 : &[0u8; 6],
966 4 : VisitDirection::Forwards,
967 32 : |key, value| {
968 32 : data.push((key.to_vec(), value));
969 32 : true
970 32 : },
971 4 : &ctx,
972 4 : )
973 4 : .await?;
974 4 : assert_eq!(data, expected);
975 4 :
976 4 : Ok(())
977 4 : }
978 :
979 : #[tokio::test]
980 4 : async fn lots_of_keys() -> Result<()> {
981 4 : let mut disk = TestDisk::new();
982 4 : let mut writer = DiskBtreeBuilder::<_, 8>::new(&mut disk);
983 4 : let ctx =
984 4 : RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error).with_scope_unit_test();
985 4 :
986 4 : const NUM_KEYS: u64 = 1000;
987 4 :
988 4 : let mut all_data: BTreeMap<u64, u64> = BTreeMap::new();
989 4 :
990 4004 : for idx in 0..NUM_KEYS {
991 4000 : let key_int: u64 = 1 + idx * 2;
992 4000 : let key = u64::to_be_bytes(key_int);
993 4000 : writer.append(&key, idx)?;
994 4 :
995 4000 : all_data.insert(key_int, idx);
996 4 : }
997 4 :
998 4 : let (root_offset, _writer) = writer.finish()?;
999 4 :
1000 4 : let reader = DiskBtreeReader::new(0, root_offset, disk);
1001 4 :
1002 4 : reader.dump(&ctx).await?;
1003 4 :
1004 4 : use std::sync::Mutex;
1005 4 :
1006 4 : let result = Mutex::new(Vec::new());
1007 4 : let limit: AtomicUsize = AtomicUsize::new(10);
1008 167640 : let take_ten = |key: &[u8], value: u64| {
1009 167640 : let mut keybuf = [0u8; 8];
1010 167640 : keybuf.copy_from_slice(key);
1011 167640 : let key_int = u64::from_be_bytes(keybuf);
1012 167640 :
1013 167640 : let mut result = result.lock().unwrap();
1014 167640 : result.push((key_int, value));
1015 167640 :
1016 167640 : // keep going until we have 10 matches
1017 167640 : result.len() < limit.load(Ordering::Relaxed)
1018 167640 : };
1019 4 :
1020 8040 : for search_key_int in 0..(NUM_KEYS * 2 + 10) {
1021 8040 : let search_key = u64::to_be_bytes(search_key_int);
1022 8040 : assert_eq!(
1023 8040 : reader.get(&search_key, &ctx).await?,
1024 8040 : all_data.get(&search_key_int).cloned()
1025 4 : );
1026 4 :
1027 4 : // Test a forward scan starting with this key
1028 8040 : result.lock().unwrap().clear();
1029 8040 : reader
1030 8040 : .visit(&search_key, VisitDirection::Forwards, take_ten, &ctx)
1031 8040 : .await?;
1032 8040 : let expected = all_data
1033 8040 : .range(search_key_int..)
1034 8040 : .take(10)
1035 79640 : .map(|(&key, &val)| (key, val))
1036 8040 : .collect::<Vec<(u64, u64)>>();
1037 8040 : assert_eq!(*result.lock().unwrap(), expected);
1038 4 :
1039 4 : // And a backwards scan
1040 8040 : result.lock().unwrap().clear();
1041 8040 : reader
1042 8040 : .visit(&search_key, VisitDirection::Backwards, take_ten, &ctx)
1043 8040 : .await?;
1044 8040 : let expected = all_data
1045 8040 : .range(..=search_key_int)
1046 8040 : .rev()
1047 8040 : .take(10)
1048 80000 : .map(|(&key, &val)| (key, val))
1049 8040 : .collect::<Vec<(u64, u64)>>();
1050 8040 : assert_eq!(*result.lock().unwrap(), expected);
1051 4 : }
1052 4 :
1053 4 : // full scan
1054 4 : let search_key = u64::to_be_bytes(0);
1055 4 : limit.store(usize::MAX, Ordering::Relaxed);
1056 4 : result.lock().unwrap().clear();
1057 4 : reader
1058 4 : .visit(&search_key, VisitDirection::Forwards, take_ten, &ctx)
1059 4 : .await?;
1060 4 : let expected = all_data
1061 4 : .iter()
1062 4000 : .map(|(&key, &val)| (key, val))
1063 4 : .collect::<Vec<(u64, u64)>>();
1064 4 : assert_eq!(*result.lock().unwrap(), expected);
1065 4 :
1066 4 : // full scan
1067 4 : let search_key = u64::to_be_bytes(u64::MAX);
1068 4 : limit.store(usize::MAX, Ordering::Relaxed);
1069 4 : result.lock().unwrap().clear();
1070 4 : reader
1071 4 : .visit(&search_key, VisitDirection::Backwards, take_ten, &ctx)
1072 4 : .await?;
1073 4 : let expected = all_data
1074 4 : .iter()
1075 4 : .rev()
1076 4000 : .map(|(&key, &val)| (key, val))
1077 4 : .collect::<Vec<(u64, u64)>>();
1078 4 : assert_eq!(*result.lock().unwrap(), expected);
1079 4 :
1080 4 : Ok(())
1081 4 : }
1082 :
1083 : #[tokio::test]
1084 4 : async fn random_data() -> Result<()> {
1085 4 : let ctx = RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error);
1086 4 :
1087 4 : // Generate random keys with exponential distribution, to
1088 4 : // exercise the prefix compression
1089 4 : const NUM_KEYS: usize = 100000;
1090 4 : let mut all_data: BTreeMap<u128, u64> = BTreeMap::new();
1091 400004 : for idx in 0..NUM_KEYS {
1092 400000 : let u: f64 = rand::thread_rng().gen_range(0.0..1.0);
1093 400000 : let t = -(f64::ln(u));
1094 400000 : let key_int = (t * 1000000.0) as u128;
1095 400000 :
1096 400000 : all_data.insert(key_int, idx as u64);
1097 400000 : }
1098 4 :
1099 4 : // Build a tree from it
1100 4 : let mut disk = TestDisk::new();
1101 4 : let mut writer = DiskBtreeBuilder::<_, 16>::new(&mut disk);
1102 4 :
1103 390237 : for (&key, &val) in all_data.iter() {
1104 390237 : writer.append(&u128::to_be_bytes(key), val)?;
1105 4 : }
1106 4 : let (root_offset, _writer) = writer.finish()?;
1107 4 :
1108 4 : let reader = DiskBtreeReader::new(0, root_offset, disk);
1109 4 :
1110 4 : // Test get() operation on all the keys
1111 390237 : for (&key, &val) in all_data.iter() {
1112 390237 : let search_key = u128::to_be_bytes(key);
1113 390237 : assert_eq!(reader.get(&search_key, &ctx).await?, Some(val));
1114 4 : }
1115 4 :
1116 4 : // Test get() operations on random keys, most of which will not exist
1117 400004 : for _ in 0..100000 {
1118 400000 : let key_int = rand::thread_rng().r#gen::<u128>();
1119 400000 : let search_key = u128::to_be_bytes(key_int);
1120 400000 : assert!(reader.get(&search_key, &ctx).await? == all_data.get(&key_int).cloned());
1121 4 : }
1122 4 :
1123 4 : // Test boundary cases
1124 4 : assert!(
1125 4 : reader.get(&u128::to_be_bytes(u128::MIN), &ctx).await?
1126 4 : == all_data.get(&u128::MIN).cloned()
1127 4 : );
1128 4 : assert!(
1129 4 : reader.get(&u128::to_be_bytes(u128::MAX), &ctx).await?
1130 4 : == all_data.get(&u128::MAX).cloned()
1131 4 : );
1132 4 :
1133 4 : // Test iterator and get_stream API
1134 4 : let mut iter = reader.iter(&[0; 16], &ctx);
1135 4 : let mut cnt = 0;
1136 390241 : while let Some(res) = iter.next().await {
1137 390237 : let (key, val) = res?;
1138 390237 : let key = u128::from_be_bytes(key.as_slice().try_into().unwrap());
1139 390237 : assert_eq!(val, *all_data.get(&key).unwrap());
1140 390237 : cnt += 1;
1141 4 : }
1142 4 : assert_eq!(cnt, all_data.len());
1143 4 :
1144 4 : Ok(())
1145 4 : }
1146 :
1147 : #[test]
1148 4 : fn unsorted_input() {
1149 4 : let mut disk = TestDisk::new();
1150 4 : let mut writer = DiskBtreeBuilder::<_, 2>::new(&mut disk);
1151 4 :
1152 4 : let _ = writer.append(b"ba", 1);
1153 4 : let _ = writer.append(b"bb", 2);
1154 4 : let err = writer.append(b"aa", 3).expect_err("should've failed");
1155 4 : match err {
1156 4 : DiskBtreeError::UnsortedInput { key, last_key } => {
1157 4 : assert_eq!(key.as_ref(), b"aa".as_slice());
1158 4 : assert_eq!(last_key.as_ref(), b"bb".as_slice());
1159 : }
1160 0 : _ => panic!("unexpected error variant, expected DiskBtreeError::UnsortedInput"),
1161 : }
1162 4 : }
1163 :
1164 : ///
1165 : /// This test contains a particular data set, see disk_btree_test_data.rs
1166 : ///
1167 : #[tokio::test]
1168 4 : async fn particular_data() -> Result<()> {
1169 4 : // Build a tree from it
1170 4 : let mut disk = TestDisk::new();
1171 4 : let mut writer = DiskBtreeBuilder::<_, 26>::new(&mut disk);
1172 4 : let ctx =
1173 4 : RequestContext::new(TaskKind::UnitTest, DownloadBehavior::Error).with_scope_unit_test();
1174 4 :
1175 8004 : for (key, val) in disk_btree_test_data::TEST_DATA {
1176 8000 : writer.append(&key, val)?;
1177 4 : }
1178 4 : let (root_offset, writer) = writer.finish()?;
1179 4 :
1180 4 : println!("SIZE: {} blocks", writer.blocks.len());
1181 4 :
1182 4 : let reader = DiskBtreeReader::new(0, root_offset, disk);
1183 4 :
1184 4 : // Test get() operation on all the keys
1185 8004 : for (key, val) in disk_btree_test_data::TEST_DATA {
1186 8000 : assert_eq!(reader.get(&key, &ctx).await?, Some(val));
1187 4 : }
1188 4 :
1189 4 : // Test full scan
1190 4 : let mut count = 0;
1191 4 : reader
1192 4 : .visit(
1193 4 : &[0u8; 26],
1194 4 : VisitDirection::Forwards,
1195 8000 : |_key, _value| {
1196 8000 : count += 1;
1197 8000 : true
1198 8000 : },
1199 4 : &ctx,
1200 4 : )
1201 4 : .await?;
1202 4 : assert_eq!(count, disk_btree_test_data::TEST_DATA.len());
1203 4 :
1204 4 : reader.dump(&ctx).await?;
1205 4 :
1206 4 : Ok(())
1207 4 : }
1208 : }
1209 :
1210 : #[cfg(test)]
1211 : #[path = "disk_btree_test_data.rs"]
1212 : mod disk_btree_test_data;
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