1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

//! Pruning window.
//!
//! For each block we maintain a list of nodes pending deletion.
//! There is also a global index of node key to block number.
//! If a node is re-inserted into the window it gets removed from
//! the death list.
//! The changes are journaled in the DB.

use crate::{
	noncanonical::LAST_CANONICAL, to_meta_key, CommitSet, Error, Hash, MetaDb, StateDbError,
	DEFAULT_MAX_BLOCK_CONSTRAINT, LOG_TARGET,
};
use codec::{Decode, Encode};
use log::trace;
use std::collections::{HashMap, HashSet, VecDeque};

pub(crate) const LAST_PRUNED: &[u8] = b"last_pruned";
const PRUNING_JOURNAL: &[u8] = b"pruning_journal";

/// See module documentation.
pub struct RefWindow<BlockHash: Hash, Key: Hash, D: MetaDb> {
	/// A queue of blocks keep tracking keys that should be deleted for each block in the
	/// pruning window.
	queue: DeathRowQueue<BlockHash, Key, D>,
	/// Block number that is next to be pruned.
	base: u64,
}

/// `DeathRowQueue` used to keep track of blocks in the pruning window, there are two flavors:
/// - `Mem`, used when the backend database do not supports reference counting, keep all
/// 	blocks in memory, and keep track of re-inserted keys to not delete them when pruning
/// - `DbBacked`, used when the backend database supports reference counting, only keep
/// 	a few number of blocks in memory and load more blocks on demand
enum DeathRowQueue<BlockHash: Hash, Key: Hash, D: MetaDb> {
	Mem {
		/// A queue of keys that should be deleted for each block in the pruning window.
		death_rows: VecDeque<DeathRow<BlockHash, Key>>,
		/// An index that maps each key from `death_rows` to block number.
		death_index: HashMap<Key, u64>,
	},
	DbBacked {
		// The backend database
		db: D,
		/// A queue of keys that should be deleted for each block in the pruning window.
		/// Only caching the first few blocks of the pruning window, blocks inside are
		/// successive and ordered by block number
		cache: VecDeque<DeathRow<BlockHash, Key>>,
		/// A soft limit of the cache's size
		cache_capacity: usize,
		/// Last block number added to the window
		last: Option<u64>,
	},
}

impl<BlockHash: Hash, Key: Hash, D: MetaDb> DeathRowQueue<BlockHash, Key, D> {
	/// Return a `DeathRowQueue` that all blocks are keep in memory
	fn new_mem(db: &D, base: u64) -> Result<DeathRowQueue<BlockHash, Key, D>, Error<D::Error>> {
		let mut block = base;
		let mut queue = DeathRowQueue::<BlockHash, Key, D>::Mem {
			death_rows: VecDeque::new(),
			death_index: HashMap::new(),
		};
		// read the journal
		trace!(
			target: LOG_TARGET,
			"Reading pruning journal for the memory queue. Pending #{}",
			base,
		);
		loop {
			let journal_key = to_journal_key(block);
			match db.get_meta(&journal_key).map_err(Error::Db)? {
				Some(record) => {
					let record: JournalRecord<BlockHash, Key> =
						Decode::decode(&mut record.as_slice())?;
					trace!(
						target: LOG_TARGET,
						"Pruning journal entry {} ({} inserted, {} deleted)",
						block,
						record.inserted.len(),
						record.deleted.len(),
					);
					queue.import(base, block, record);
				},
				None => break,
			}
			block += 1;
		}
		Ok(queue)
	}

	/// Return a `DeathRowQueue` that backed by an database, and only keep a few number
	/// of blocks in memory
	fn new_db_backed(
		db: D,
		base: u64,
		last: Option<u64>,
		window_size: u32,
	) -> Result<DeathRowQueue<BlockHash, Key, D>, Error<D::Error>> {
		// limit the cache capacity from 1 to `DEFAULT_MAX_BLOCK_CONSTRAINT`
		let cache_capacity = window_size.clamp(1, DEFAULT_MAX_BLOCK_CONSTRAINT) as usize;
		let mut cache = VecDeque::with_capacity(cache_capacity);
		trace!(
			target: LOG_TARGET,
			"Reading pruning journal for the database-backed queue. Pending #{}",
			base
		);
		DeathRowQueue::load_batch_from_db(&db, &mut cache, base, cache_capacity)?;
		Ok(DeathRowQueue::DbBacked { db, cache, cache_capacity, last })
	}

	/// import a new block to the back of the queue
	fn import(&mut self, base: u64, num: u64, journal_record: JournalRecord<BlockHash, Key>) {
		let JournalRecord { hash, inserted, deleted } = journal_record;
		trace!(target: LOG_TARGET, "Importing {}, base={}", num, base);
		match self {
			DeathRowQueue::DbBacked { cache, cache_capacity, last, .. } => {
				// If the new block continues cached range and there is space, load it directly into
				// cache.
				if num == base + cache.len() as u64 && cache.len() < *cache_capacity {
					trace!(target: LOG_TARGET, "Adding to DB backed cache {:?} (#{})", hash, num);
					cache.push_back(DeathRow { hash, deleted: deleted.into_iter().collect() });
				}
				*last = Some(num);
			},
			DeathRowQueue::Mem { death_rows, death_index } => {
				// remove all re-inserted keys from death rows
				for k in inserted {
					if let Some(block) = death_index.remove(&k) {
						death_rows[(block - base) as usize].deleted.remove(&k);
					}
				}
				// add new keys
				let imported_block = base + death_rows.len() as u64;
				for k in deleted.iter() {
					death_index.insert(k.clone(), imported_block);
				}
				death_rows.push_back(DeathRow { hash, deleted: deleted.into_iter().collect() });
			},
		}
	}

	/// Pop out one block from the front of the queue, `base` is the block number
	/// of the first block of the queue
	fn pop_front(
		&mut self,
		base: u64,
	) -> Result<Option<DeathRow<BlockHash, Key>>, Error<D::Error>> {
		match self {
			DeathRowQueue::DbBacked { db, cache, cache_capacity, .. } => {
				if cache.is_empty() {
					DeathRowQueue::load_batch_from_db(db, cache, base, *cache_capacity)?;
				}
				Ok(cache.pop_front())
			},
			DeathRowQueue::Mem { death_rows, death_index } => match death_rows.pop_front() {
				Some(row) => {
					for k in row.deleted.iter() {
						death_index.remove(k);
					}
					Ok(Some(row))
				},
				None => Ok(None),
			},
		}
	}

	/// Load a batch of blocks from the backend database into `cache`, starting from `base` and up
	/// to `base + cache_capacity`
	fn load_batch_from_db(
		db: &D,
		cache: &mut VecDeque<DeathRow<BlockHash, Key>>,
		base: u64,
		cache_capacity: usize,
	) -> Result<(), Error<D::Error>> {
		let start = base + cache.len() as u64;
		let batch_size = cache_capacity;
		for i in 0..batch_size as u64 {
			match load_death_row_from_db::<BlockHash, Key, D>(db, start + i)? {
				Some(row) => {
					cache.push_back(row);
				},
				None => break,
			}
		}
		Ok(())
	}

	/// Check if the block at the given `index` of the queue exist
	/// it is the caller's responsibility to ensure `index` won't be out of bounds
	fn have_block(&self, hash: &BlockHash, index: usize) -> HaveBlock {
		match self {
			DeathRowQueue::DbBacked { cache, .. } => {
				if cache.len() > index {
					(cache[index].hash == *hash).into()
				} else {
					// The block is not in the cache but it still may exist on disk.
					HaveBlock::Maybe
				}
			},
			DeathRowQueue::Mem { death_rows, .. } => (death_rows[index].hash == *hash).into(),
		}
	}

	/// Return the number of block in the pruning window
	fn len(&self, base: u64) -> u64 {
		match self {
			DeathRowQueue::DbBacked { last, .. } => last.map_or(0, |l| l + 1 - base),
			DeathRowQueue::Mem { death_rows, .. } => death_rows.len() as u64,
		}
	}

	#[cfg(test)]
	fn get_mem_queue_state(
		&self,
	) -> Option<(&VecDeque<DeathRow<BlockHash, Key>>, &HashMap<Key, u64>)> {
		match self {
			DeathRowQueue::DbBacked { .. } => None,
			DeathRowQueue::Mem { death_rows, death_index } => Some((death_rows, death_index)),
		}
	}

	#[cfg(test)]
	fn get_db_backed_queue_state(
		&self,
	) -> Option<(&VecDeque<DeathRow<BlockHash, Key>>, Option<u64>)> {
		match self {
			DeathRowQueue::DbBacked { cache, last, .. } => Some((cache, *last)),
			DeathRowQueue::Mem { .. } => None,
		}
	}
}

fn load_death_row_from_db<BlockHash: Hash, Key: Hash, D: MetaDb>(
	db: &D,
	block: u64,
) -> Result<Option<DeathRow<BlockHash, Key>>, Error<D::Error>> {
	let journal_key = to_journal_key(block);
	match db.get_meta(&journal_key).map_err(Error::Db)? {
		Some(record) => {
			let JournalRecord { hash, deleted, .. } = Decode::decode(&mut record.as_slice())?;
			Ok(Some(DeathRow { hash, deleted: deleted.into_iter().collect() }))
		},
		None => Ok(None),
	}
}

#[derive(Clone, Debug, PartialEq, Eq)]
struct DeathRow<BlockHash: Hash, Key: Hash> {
	hash: BlockHash,
	deleted: HashSet<Key>,
}

#[derive(Encode, Decode, Default)]
struct JournalRecord<BlockHash: Hash, Key: Hash> {
	hash: BlockHash,
	inserted: Vec<Key>,
	deleted: Vec<Key>,
}

fn to_journal_key(block: u64) -> Vec<u8> {
	to_meta_key(PRUNING_JOURNAL, &block)
}

/// The result return by `RefWindow::have_block`
#[derive(Debug, PartialEq, Eq)]
pub enum HaveBlock {
	/// Definitely don't have this block.
	No,
	/// May or may not have this block, need further checking
	Maybe,
	/// Definitely has this block
	Yes,
}

impl From<bool> for HaveBlock {
	fn from(have: bool) -> Self {
		if have {
			HaveBlock::Yes
		} else {
			HaveBlock::No
		}
	}
}

impl<BlockHash: Hash, Key: Hash, D: MetaDb> RefWindow<BlockHash, Key, D> {
	pub fn new(
		db: D,
		window_size: u32,
		count_insertions: bool,
	) -> Result<RefWindow<BlockHash, Key, D>, Error<D::Error>> {
		// the block number of the first block in the queue or the next block number if the queue is
		// empty
		let base = match db.get_meta(&to_meta_key(LAST_PRUNED, &())).map_err(Error::Db)? {
			Some(buffer) => u64::decode(&mut buffer.as_slice())? + 1,
			None => 0,
		};
		// the block number of the last block in the queue
		let last_canonicalized_number =
			match db.get_meta(&to_meta_key(LAST_CANONICAL, &())).map_err(Error::Db)? {
				Some(buffer) => Some(<(BlockHash, u64)>::decode(&mut buffer.as_slice())?.1),
				None => None,
			};

		let queue = if count_insertions {
			// Highly scientific crafted number for deciding when to print the warning!
			//
			// Rocksdb doesn't support refcounting and requires that we load the entire pruning
			// window into the memory.
			if window_size > 1000 {
				log::warn!(
					target: LOG_TARGET,
					"Large pruning window of {window_size} detected! THIS CAN LEAD TO HIGH MEMORY USAGE AND CRASHES. \
					Reduce the pruning window or switch your database to paritydb."
				);
			}

			DeathRowQueue::new_mem(&db, base)?
		} else {
			let last = match last_canonicalized_number {
				Some(last_canonicalized_number) => {
					debug_assert!(last_canonicalized_number + 1 >= base);
					Some(last_canonicalized_number)
				},
				// None means `LAST_CANONICAL` is never been wrote, since the pruning journals are
				// in the same `CommitSet` as `LAST_CANONICAL`, it means no pruning journal have
				// ever been committed to the db, thus set `unload` to zero
				None => None,
			};
			DeathRowQueue::new_db_backed(db, base, last, window_size)?
		};

		Ok(RefWindow { queue, base })
	}

	pub fn window_size(&self) -> u64 {
		self.queue.len(self.base) as u64
	}

	/// Get the hash of the next pruning block
	pub fn next_hash(&mut self) -> Result<Option<BlockHash>, Error<D::Error>> {
		let res = match &mut self.queue {
			DeathRowQueue::DbBacked { db, cache, cache_capacity, .. } => {
				if cache.is_empty() {
					DeathRowQueue::load_batch_from_db(db, cache, self.base, *cache_capacity)?;
				}
				cache.front().map(|r| r.hash.clone())
			},
			DeathRowQueue::Mem { death_rows, .. } => death_rows.front().map(|r| r.hash.clone()),
		};
		Ok(res)
	}

	fn is_empty(&self) -> bool {
		self.window_size() == 0
	}

	// Check if a block is in the pruning window and not be pruned yet
	pub fn have_block(&self, hash: &BlockHash, number: u64) -> HaveBlock {
		// if the queue is empty or the block number exceed the pruning window, we definitely
		// do not have this block
		if self.is_empty() || number < self.base || number >= self.base + self.window_size() {
			return HaveBlock::No
		}
		self.queue.have_block(hash, (number - self.base) as usize)
	}

	/// Prune next block. Expects at least one block in the window. Adds changes to `commit`.
	pub fn prune_one(&mut self, commit: &mut CommitSet<Key>) -> Result<(), Error<D::Error>> {
		if let Some(pruned) = self.queue.pop_front(self.base)? {
			trace!(target: LOG_TARGET, "Pruning {:?} ({} deleted)", pruned.hash, pruned.deleted.len());
			let index = self.base;
			commit.data.deleted.extend(pruned.deleted.into_iter());
			commit.meta.inserted.push((to_meta_key(LAST_PRUNED, &()), index.encode()));
			commit.meta.deleted.push(to_journal_key(self.base));
			self.base += 1;
			Ok(())
		} else {
			trace!(target: LOG_TARGET, "Trying to prune when there's nothing to prune");
			Err(Error::StateDb(StateDbError::BlockUnavailable))
		}
	}

	/// Add a change set to the window. Creates a journal record and pushes it to `commit`
	pub fn note_canonical(
		&mut self,
		hash: &BlockHash,
		number: u64,
		commit: &mut CommitSet<Key>,
	) -> Result<(), Error<D::Error>> {
		if self.base == 0 && self.is_empty() && number > 0 {
			// This branch is taken if the node imports the target block of a warp sync.
			// assume that the block was canonicalized
			self.base = number;
			// The parent of the block was the last block that got pruned.
			commit
				.meta
				.inserted
				.push((to_meta_key(LAST_PRUNED, &()), (number - 1).encode()));
		} else if (self.base + self.window_size()) != number {
			return Err(Error::StateDb(StateDbError::InvalidBlockNumber))
		}
		trace!(
			target: LOG_TARGET,
			"Adding to pruning window: {:?} ({} inserted, {} deleted)",
			hash,
			commit.data.inserted.len(),
			commit.data.deleted.len(),
		);
		let inserted = if matches!(self.queue, DeathRowQueue::Mem { .. }) {
			commit.data.inserted.iter().map(|(k, _)| k.clone()).collect()
		} else {
			Default::default()
		};
		let deleted = std::mem::take(&mut commit.data.deleted);
		let journal_record = JournalRecord { hash: hash.clone(), inserted, deleted };
		commit.meta.inserted.push((to_journal_key(number), journal_record.encode()));
		self.queue.import(self.base, number, journal_record);
		Ok(())
	}
}

#[cfg(test)]
mod tests {
	use super::{to_journal_key, DeathRowQueue, HaveBlock, JournalRecord, RefWindow, LAST_PRUNED};
	use crate::{
		noncanonical::LAST_CANONICAL,
		test::{make_commit, make_db, TestDb},
		to_meta_key, CommitSet, Error, Hash, StateDbError, DEFAULT_MAX_BLOCK_CONSTRAINT,
	};
	use codec::Encode;
	use sp_core::H256;

	fn check_journal(pruning: &RefWindow<H256, H256, TestDb>, db: &TestDb) {
		let count_insertions = matches!(pruning.queue, DeathRowQueue::Mem { .. });
		let restored: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, count_insertions).unwrap();
		assert_eq!(pruning.base, restored.base);
		assert_eq!(pruning.queue.get_mem_queue_state(), restored.queue.get_mem_queue_state());
	}

	#[test]
	fn created_from_empty_db() {
		let db = make_db(&[]);
		let pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db, DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		assert_eq!(pruning.base, 0);
		let (death_rows, death_index) = pruning.queue.get_mem_queue_state().unwrap();
		assert!(death_rows.is_empty());
		assert!(death_index.is_empty());
	}

	#[test]
	fn prune_empty() {
		let db = make_db(&[]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db, DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		let mut commit = CommitSet::default();
		assert_eq!(
			Err(Error::StateDb(StateDbError::BlockUnavailable)),
			pruning.prune_one(&mut commit)
		);
		assert_eq!(pruning.base, 0);
		let (death_rows, death_index) = pruning.queue.get_mem_queue_state().unwrap();
		assert!(death_rows.is_empty());
		assert!(death_index.is_empty());
	}

	#[test]
	fn prune_one() {
		let mut db = make_db(&[1, 2, 3]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		let mut commit = make_commit(&[4, 5], &[1, 3]);
		let hash = H256::random();
		pruning.note_canonical(&hash, 0, &mut commit).unwrap();
		db.commit(&commit);
		assert_eq!(pruning.have_block(&hash, 0), HaveBlock::Yes);
		assert_eq!(pruning.have_block(&hash, 0), HaveBlock::Yes);
		assert!(commit.data.deleted.is_empty());
		let (death_rows, death_index) = pruning.queue.get_mem_queue_state().unwrap();
		assert_eq!(death_rows.len(), 1);
		assert_eq!(death_index.len(), 2);
		assert!(db.data_eq(&make_db(&[1, 2, 3, 4, 5])));
		check_journal(&pruning, &db);

		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		assert_eq!(pruning.have_block(&hash, 0), HaveBlock::No);
		db.commit(&commit);
		assert_eq!(pruning.have_block(&hash, 0), HaveBlock::No);
		assert!(db.data_eq(&make_db(&[2, 4, 5])));
		let (death_rows, death_index) = pruning.queue.get_mem_queue_state().unwrap();
		assert!(death_rows.is_empty());
		assert!(death_index.is_empty());
		assert_eq!(pruning.base, 1);
	}

	#[test]
	fn prune_two() {
		let mut db = make_db(&[1, 2, 3]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		let mut commit = make_commit(&[4], &[1]);
		pruning.note_canonical(&H256::random(), 0, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[5], &[2]);
		pruning.note_canonical(&H256::random(), 1, &mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3, 4, 5])));

		check_journal(&pruning, &db);

		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[2, 3, 4, 5])));
		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[3, 4, 5])));
		assert_eq!(pruning.base, 2);
	}

	#[test]
	fn prune_two_pending() {
		let mut db = make_db(&[1, 2, 3]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		let mut commit = make_commit(&[4], &[1]);
		pruning.note_canonical(&H256::random(), 0, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[5], &[2]);
		pruning.note_canonical(&H256::random(), 1, &mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3, 4, 5])));
		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[2, 3, 4, 5])));
		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[3, 4, 5])));
		assert_eq!(pruning.base, 2);
	}

	#[test]
	fn reinserted_survives() {
		let mut db = make_db(&[1, 2, 3]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		let mut commit = make_commit(&[], &[2]);
		pruning.note_canonical(&H256::random(), 0, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[2], &[]);
		pruning.note_canonical(&H256::random(), 1, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[], &[2]);
		pruning.note_canonical(&H256::random(), 2, &mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));

		check_journal(&pruning, &db);

		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));
		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 3])));
		assert_eq!(pruning.base, 3);
	}

	#[test]
	fn reinserted_survive_pending() {
		let mut db = make_db(&[1, 2, 3]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, true).unwrap();
		let mut commit = make_commit(&[], &[2]);
		pruning.note_canonical(&H256::random(), 0, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[2], &[]);
		pruning.note_canonical(&H256::random(), 1, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[], &[2]);
		pruning.note_canonical(&H256::random(), 2, &mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));

		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));
		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 3])));
		assert_eq!(pruning.base, 3);
	}

	#[test]
	fn reinserted_ignores() {
		let mut db = make_db(&[1, 2, 3]);
		let mut pruning: RefWindow<H256, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		let mut commit = make_commit(&[], &[2]);
		pruning.note_canonical(&H256::random(), 0, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[2], &[]);
		pruning.note_canonical(&H256::random(), 1, &mut commit).unwrap();
		db.commit(&commit);
		let mut commit = make_commit(&[], &[2]);
		pruning.note_canonical(&H256::random(), 2, &mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 2, 3])));

		check_journal(&pruning, &db);

		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert!(db.data_eq(&make_db(&[1, 3])));
	}

	fn push_last_canonicalized<H: Hash>(block: u64, commit: &mut CommitSet<H>) {
		commit
			.meta
			.inserted
			.push((to_meta_key(LAST_CANONICAL, &()), (block, block).encode()));
	}

	fn push_last_pruned<H: Hash>(block: u64, commit: &mut CommitSet<H>) {
		commit.meta.inserted.push((to_meta_key(LAST_PRUNED, &()), block.encode()));
	}

	#[test]
	fn init_db_backed_queue() {
		let mut db = make_db(&[]);
		let mut commit = CommitSet::default();

		fn load_pruning_from_db(db: TestDb) -> (usize, u64) {
			let pruning: RefWindow<u64, H256, TestDb> =
				RefWindow::new(db, DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
			let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
			(cache.len(), pruning.base)
		}

		fn push_record(block: u64, commit: &mut CommitSet<H256>) {
			commit
				.meta
				.inserted
				.push((to_journal_key(block), JournalRecord::<u64, H256>::default().encode()));
		}

		// empty database
		let (loaded_blocks, base) = load_pruning_from_db(db.clone());
		assert_eq!(loaded_blocks, 0);
		assert_eq!(base, 0);

		// canonicalized the genesis block but no pruning
		push_last_canonicalized(0, &mut commit);
		push_record(0, &mut commit);
		db.commit(&commit);
		let (loaded_blocks, base) = load_pruning_from_db(db.clone());
		assert_eq!(loaded_blocks, 1);
		assert_eq!(base, 0);

		// pruned the genesis block
		push_last_pruned(0, &mut commit);
		db.commit(&commit);
		let (loaded_blocks, base) = load_pruning_from_db(db.clone());
		assert_eq!(loaded_blocks, 0);
		assert_eq!(base, 1);

		// canonicalize more blocks
		push_last_canonicalized(10, &mut commit);
		for i in 1..=10 {
			push_record(i, &mut commit);
		}
		db.commit(&commit);
		let (loaded_blocks, base) = load_pruning_from_db(db.clone());
		assert_eq!(loaded_blocks, 10);
		assert_eq!(base, 1);

		// pruned all blocks
		push_last_pruned(10, &mut commit);
		db.commit(&commit);
		let (loaded_blocks, base) = load_pruning_from_db(db.clone());
		assert_eq!(loaded_blocks, 0);
		assert_eq!(base, 11);
	}

	#[test]
	fn db_backed_queue() {
		let mut db = make_db(&[]);
		let mut pruning: RefWindow<u64, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		let cache_capacity = DEFAULT_MAX_BLOCK_CONSTRAINT as usize;

		// start as an empty queue
		let (cache, last) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), 0);
		assert_eq!(last, None);

		// import blocks
		// queue size and content should match
		for i in 0..(cache_capacity + 10) {
			let mut commit = make_commit(&[], &[]);
			pruning.note_canonical(&(i as u64), i as u64, &mut commit).unwrap();
			push_last_canonicalized(i as u64, &mut commit);
			db.commit(&commit);
			// blocks will fill the cache first
			let (cache, last) = pruning.queue.get_db_backed_queue_state().unwrap();
			if i < cache_capacity {
				assert_eq!(cache.len(), i + 1);
			} else {
				assert_eq!(cache.len(), cache_capacity);
			}
			assert_eq!(last, Some(i as u64));
		}
		assert_eq!(pruning.window_size(), cache_capacity as u64 + 10);
		let (cache, last) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), cache_capacity);
		assert_eq!(last, Some(cache_capacity as u64 + 10 - 1));
		for i in 0..cache_capacity {
			assert_eq!(cache[i].hash, i as u64);
		}

		// import a new block to the end of the queue
		// won't keep the new block in memory
		let mut commit = CommitSet::default();
		pruning
			.note_canonical(&(cache_capacity as u64 + 10), cache_capacity as u64 + 10, &mut commit)
			.unwrap();
		assert_eq!(pruning.window_size(), cache_capacity as u64 + 11);
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), cache_capacity);

		// revert the last add that no apply yet
		// NOTE: do not commit the previous `CommitSet` to db
		pruning = RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		let cache_capacity = DEFAULT_MAX_BLOCK_CONSTRAINT as usize;
		assert_eq!(pruning.window_size(), cache_capacity as u64 + 10);
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), cache_capacity);

		// remove one block from the start of the queue
		// block is removed from the head of cache
		let mut commit = CommitSet::default();
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
		assert_eq!(pruning.window_size(), cache_capacity as u64 + 9);
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), cache_capacity - 1);
		for i in 0..(cache_capacity - 1) {
			assert_eq!(cache[i].hash, (i + 1) as u64);
		}

		// load a new queue from db
		// `cache` is full again but the content of the queue should be the same
		let pruning: RefWindow<u64, H256, TestDb> =
			RefWindow::new(db, DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		assert_eq!(pruning.window_size(), cache_capacity as u64 + 9);
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), cache_capacity);
		for i in 0..cache_capacity {
			assert_eq!(cache[i].hash, (i + 1) as u64);
		}
	}

	#[test]
	fn load_block_from_db() {
		let mut db = make_db(&[]);
		let mut pruning: RefWindow<u64, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		let cache_capacity = DEFAULT_MAX_BLOCK_CONSTRAINT as usize;

		// import blocks
		for i in 0..(cache_capacity as u64 * 2 + 10) {
			let mut commit = make_commit(&[], &[]);
			pruning.note_canonical(&i, i, &mut commit).unwrap();
			push_last_canonicalized(i as u64, &mut commit);
			db.commit(&commit);
		}

		// the following operations won't trigger loading block from db:
		// - getting block in cache
		// - getting block not in the queue
		assert_eq!(pruning.next_hash().unwrap().unwrap(), 0);
		let (cache, last) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), cache_capacity);
		assert_eq!(last, Some(cache_capacity as u64 * 2 + 10 - 1));

		// clear all block loaded in cache
		for _ in 0..cache_capacity * 2 {
			let mut commit = CommitSet::default();
			pruning.prune_one(&mut commit).unwrap();
			db.commit(&commit);
		}
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert!(cache.is_empty());

		// getting the hash of block that not in cache will also trigger loading
		// the remaining blocks from db
		assert_eq!(pruning.next_hash().unwrap().unwrap(), (cache_capacity * 2) as u64);
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), 10);

		// load a new queue from db
		// `cache` should be the same
		let pruning: RefWindow<u64, H256, TestDb> =
			RefWindow::new(db, DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		assert_eq!(pruning.window_size(), 10);
		let (cache, _) = pruning.queue.get_db_backed_queue_state().unwrap();
		assert_eq!(cache.len(), 10);
		for i in 0..10 {
			assert_eq!(cache[i].hash, (cache_capacity * 2 + i) as u64);
		}
	}

	#[test]
	fn get_block_from_queue() {
		let mut db = make_db(&[]);
		let mut pruning: RefWindow<u64, H256, TestDb> =
			RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, false).unwrap();
		let cache_capacity = DEFAULT_MAX_BLOCK_CONSTRAINT as u64;

		// import blocks and commit to db
		let mut commit = make_commit(&[], &[]);
		for i in 0..(cache_capacity + 10) {
			pruning.note_canonical(&i, i, &mut commit).unwrap();
		}
		db.commit(&commit);

		// import a block but not commit to db yet
		let mut pending_commit = make_commit(&[], &[]);
		let index = cache_capacity + 10;
		pruning.note_canonical(&index, index, &mut pending_commit).unwrap();

		let mut commit = make_commit(&[], &[]);
		// prune blocks that had committed to db
		for i in 0..(cache_capacity + 10) {
			assert_eq!(pruning.next_hash().unwrap(), Some(i));
			pruning.prune_one(&mut commit).unwrap();
		}
		// return `None` for block that did not commit to db
		assert_eq!(pruning.next_hash().unwrap(), None);
		assert_eq!(
			pruning.prune_one(&mut commit).unwrap_err(),
			Error::StateDb(StateDbError::BlockUnavailable)
		);
		// commit block to db and no error return
		db.commit(&pending_commit);
		assert_eq!(pruning.next_hash().unwrap(), Some(index));
		pruning.prune_one(&mut commit).unwrap();
		db.commit(&commit);
	}

	/// Ensure that after warp syncing the state is stored correctly in the db. The warp sync target
	/// block is imported with all its state at once. This test ensures that after a restart
	/// `pruning` still knows that this block was imported.
	#[test]
	fn store_correct_state_after_warp_syncing() {
		for count_insertions in [true, false] {
			let mut db = make_db(&[]);
			let mut pruning: RefWindow<u64, H256, TestDb> =
				RefWindow::new(db.clone(), DEFAULT_MAX_BLOCK_CONSTRAINT, count_insertions).unwrap();
			let block = 10000;

			// import blocks
			let mut commit = make_commit(&[], &[]);
			pruning.note_canonical(&block, block, &mut commit).unwrap();
			push_last_canonicalized(block, &mut commit);
			db.commit(&commit);

			// load a new queue from db
			// `cache` should be the same
			let pruning: RefWindow<u64, H256, TestDb> =
				RefWindow::new(db, DEFAULT_MAX_BLOCK_CONSTRAINT, count_insertions).unwrap();

			assert_eq!(HaveBlock::Yes, pruning.have_block(&block, block));
		}
	}
}