firebase-ios-sdk/Firestore/Example/Tests/Local/FSTLRUGarbageCollectorTests.mm

/*
 * Copyright 2018 Google
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#import "Firestore/Example/Tests/Local/FSTLRUGarbageCollectorTests.h"

#import <XCTest/XCTest.h>

#include <unordered_set>

#import "FIRTimestamp.h"
#import "Firestore/Example/Tests/Util/FSTHelpers.h"
#import "Firestore/Source/Local/FSTLRUGarbageCollector.h"
#import "Firestore/Source/Local/FSTMutationQueue.h"
#import "Firestore/Source/Local/FSTPersistence.h"
#import "Firestore/Source/Local/FSTQueryCache.h"
#import "Firestore/Source/Local/FSTRemoteDocumentCache.h"
#import "Firestore/Source/Model/FSTDocument.h"
#import "Firestore/Source/Model/FSTFieldValue.h"
#import "Firestore/Source/Model/FSTMutation.h"
#import "Firestore/Source/Util/FSTClasses.h"
#include "Firestore/core/src/firebase/firestore/auth/user.h"
#include "Firestore/core/src/firebase/firestore/model/document_key_set.h"
#include "Firestore/core/src/firebase/firestore/model/precondition.h"
#include "Firestore/core/src/firebase/firestore/model/types.h"
#include "Firestore/core/test/firebase/firestore/testutil/testutil.h"
#include "absl/strings/str_cat.h"

namespace testutil = firebase::firestore::testutil;
using firebase::firestore::auth::User;
using firebase::firestore::model::DocumentKey;
using firebase::firestore::model::DocumentKeyHash;
using firebase::firestore::model::DocumentKeySet;
using firebase::firestore::model::ListenSequenceNumber;
using firebase::firestore::model::Precondition;
using firebase::firestore::model::TargetId;

NS_ASSUME_NONNULL_BEGIN

@implementation FSTLRUGarbageCollectorTests {
  TargetId _previousTargetID;
  int _previousDocNum;
  FSTObjectValue *_testValue;
  FSTObjectValue *_bigObjectValue;
  id<FSTPersistence> _persistence;
  id<FSTQueryCache> _queryCache;
  id<FSTRemoteDocumentCache> _documentCache;
  id<FSTMutationQueue> _mutationQueue;
  id<FSTLRUDelegate> _lruDelegate;
  FSTLRUGarbageCollector *_gc;
  ListenSequenceNumber _initialSequenceNumber;
  User _user;
}

- (void)setUp {
  [super setUp];

  _previousTargetID = 500;
  _previousDocNum = 10;
  _testValue = FSTTestObjectValue(@{@"baz" : @YES, @"ok" : @"fine"});
  NSString *bigString = [@"" stringByPaddingToLength:4096 withString:@"a" startingAtIndex:0];
  _bigObjectValue = FSTTestObjectValue(@{@"BigProperty" : bigString});
  _user = User("user");
}

- (BOOL)isTestBaseClass {
  return ([self class] == [FSTLRUGarbageCollectorTests class]);
}

- (void)newTestResources {
  HARD_ASSERT(_persistence == nil, "Persistence already created");
  _persistence = [self newPersistence];
  _queryCache = [_persistence queryCache];
  _documentCache = [_persistence remoteDocumentCache];
  _mutationQueue = [_persistence mutationQueueForUser:_user];
  _lruDelegate = (id<FSTLRUDelegate>)_persistence.referenceDelegate;
  _initialSequenceNumber = _persistence.run("start querycache", [&]() -> ListenSequenceNumber {
    [_mutationQueue start];
    _gc = _lruDelegate.gc;
    return _persistence.currentSequenceNumber;
  });
}

- (id<FSTPersistence>)newPersistence {
  @throw FSTAbstractMethodException();  // NOLINT
}

- (BOOL)sentinelExists:(const DocumentKey &)key {
  @throw FSTAbstractMethodException();  // NOLINT
}

- (void)expectSentinelRemoved:(const DocumentKey &)key {
  XCTAssertFalse([self sentinelExists:key]);
}

#pragma mark - helpers

- (ListenSequenceNumber)sequenceNumberForQueryCount:(int)queryCount {
  return _persistence.run(
      "gc", [&]() -> ListenSequenceNumber { return [_gc sequenceNumberForQueryCount:queryCount]; });
}

- (int)queryCountForPercentile:(int)percentile {
  return _persistence.run("query count",
                          [&]() -> int { return [_gc queryCountForPercentile:percentile]; });
}

- (int)removeQueriesThroughSequenceNumber:(ListenSequenceNumber)sequenceNumber
                              liveQueries:(NSDictionary<NSNumber *, FSTQueryData *> *)liveQueries {
  return _persistence.run("gc", [&]() -> int {
    return [_gc removeQueriesUpThroughSequenceNumber:sequenceNumber liveQueries:liveQueries];
  });
}

// Removes documents that are not part of a target or a mutation and have a sequence number
// less than or equal to the given sequence number.
- (int)removeOrphanedDocumentsThroughSequenceNumber:(ListenSequenceNumber)sequenceNumber {
  return _persistence.run("gc", [&]() -> int {
    return [_gc removeOrphanedDocumentsThroughSequenceNumber:sequenceNumber];
  });
}

- (FSTQueryData *)nextTestQuery {
  TargetId targetID = ++_previousTargetID;
  ListenSequenceNumber listenSequenceNumber = _persistence.currentSequenceNumber;
  FSTQuery *query = FSTTestQuery(absl::StrCat("path", targetID));
  return [[FSTQueryData alloc] initWithQuery:query
                                    targetID:targetID
                        listenSequenceNumber:listenSequenceNumber
                                     purpose:FSTQueryPurposeListen];
}

- (FSTQueryData *)addNextQueryInTransaction {
  FSTQueryData *queryData = [self nextTestQuery];
  [_queryCache addQueryData:queryData];
  return queryData;
}

- (void)updateTargetInTransaction:(FSTQueryData *)queryData {
  NSData *token = [@"hello" dataUsingEncoding:NSUTF8StringEncoding];
  FSTQueryData *updated =
      [queryData queryDataByReplacingSnapshotVersion:queryData.snapshotVersion
                                         resumeToken:token
                                      sequenceNumber:_persistence.currentSequenceNumber];
  [_queryCache updateQueryData:updated];
}

- (FSTQueryData *)addNextQuery {
  return _persistence.run("adding query",
                          [&]() -> FSTQueryData * { return [self addNextQueryInTransaction]; });
}

// Simulates a document being mutated and then having that mutation ack'd.
// Since the document is not in a mutation queue any more, there is
// potentially nothing keeping it live. We mark it with the current sequence number
// so it can be collected later.
- (DocumentKey)markADocumentEligibleForGC {
  DocumentKey key = [self nextTestDocKey];
  [self markDocumentEligibleForGC:key];
  return key;
}

- (void)markDocumentEligibleForGC:(const DocumentKey &)docKey {
  _persistence.run("Removing mutation reference",
                   [&]() { [self markDocumentEligibleForGCInTransaction:docKey]; });
}

- (DocumentKey)markADocumentEligibleForGCInTransaction {
  DocumentKey key = [self nextTestDocKey];
  [self markDocumentEligibleForGCInTransaction:key];
  return key;
}

- (void)markDocumentEligibleForGCInTransaction:(const DocumentKey &)docKey {
  [_persistence.referenceDelegate removeMutationReference:docKey];
}

- (void)addDocument:(const DocumentKey &)docKey toTarget:(TargetId)targetId {
  [_queryCache addMatchingKeys:DocumentKeySet{docKey} forTargetID:targetId];
}

- (void)removeDocument:(const DocumentKey &)docKey fromTarget:(TargetId)targetId {
  [_queryCache removeMatchingKeys:DocumentKeySet{docKey} forTargetID:targetId];
}

/**
 * Used to insert a document into the remote document cache. Use of this method should
 * be paired with some explanation for why it is in the cache, for instance:
 * - added to a target
 * - now has or previously had a pending mutation
 */
- (FSTDocument *)cacheADocumentInTransaction {
  FSTDocument *doc = [self nextTestDocument];
  [_documentCache addEntry:doc];
  return doc;
}

- (FSTSetMutation *)mutationForDocument:(const DocumentKey &)docKey {
  return [[FSTSetMutation alloc] initWithKey:docKey
                                       value:_testValue
                                precondition:Precondition::None()];
}

- (DocumentKey)nextTestDocKey {
  return testutil::Key("docs/doc_" + std::to_string(++_previousDocNum));
}

- (FSTDocument *)nextTestDocumentWithValue:(FSTObjectValue *)value {
  DocumentKey key = [self nextTestDocKey];
  FSTTestSnapshotVersion version = 2;
  BOOL hasMutations = NO;
  return [FSTDocument documentWithData:value
                                   key:key
                               version:testutil::Version(version)
                     hasLocalMutations:hasMutations];
}

- (FSTDocument *)nextTestDocument {
  return [self nextTestDocumentWithValue:_testValue];
}

#pragma mark - tests

- (void)testPickSequenceNumberPercentile {
  if ([self isTestBaseClass]) return;

  const int numTestCases = 5;
  struct Case {
    // number of queries to cache
    int queries;
    // number expected to be calculated as 10%
    int expected;
  };
  struct Case testCases[numTestCases] = {{0, 0}, {10, 1}, {9, 0}, {50, 5}, {49, 4}};

  for (int i = 0; i < numTestCases; i++) {
    // Fill the query cache.
    int numQueries = testCases[i].queries;
    int expectedTenthPercentile = testCases[i].expected;
    [self newTestResources];
    for (int j = 0; j < numQueries; j++) {
      [self addNextQuery];
    }
    int tenth = [self queryCountForPercentile:10];
    XCTAssertEqual(expectedTenthPercentile, tenth, @"Total query count: %i", numQueries);
    [_persistence shutdown];
    _persistence = nil;
  }
}

- (void)testSequenceNumberNoQueries {
  if ([self isTestBaseClass]) return;

  // No queries... should get invalid sequence number (-1)
  [self newTestResources];
  XCTAssertEqual(kFSTListenSequenceNumberInvalid, [self sequenceNumberForQueryCount:0]);
  [_persistence shutdown];
}

- (void)testSequenceNumberForFiftyQueries {
  if ([self isTestBaseClass]) return;
  // Add 50 queries sequentially, aim to collect 10 of them.
  // The sequence number to collect should be 10 past the initial sequence number.
  [self newTestResources];
  for (int i = 0; i < 50; i++) {
    [self addNextQuery];
  }
  XCTAssertEqual(_initialSequenceNumber + 10, [self sequenceNumberForQueryCount:10]);
  [_persistence shutdown];
}

- (void)testSequenceNumberForMultipleQueriesInATransaction {
  if ([self isTestBaseClass]) return;

  // 50 queries, 9 with one transaction, incrementing from there. Should get second sequence number.
  [self newTestResources];
  _persistence.run("9 queries in a batch", [&]() {
    for (int i = 0; i < 9; i++) {
      [self addNextQueryInTransaction];
    }
  });
  for (int i = 9; i < 50; i++) {
    [self addNextQuery];
  }
  XCTAssertEqual(2 + _initialSequenceNumber, [self sequenceNumberForQueryCount:10]);
  [_persistence shutdown];
}

// Ensure that even if all of the queries are added in a single transaction, we still
// pick a sequence number and GC. In this case, the initial transaction contains all of the
// targets that will get GC'd, since they account for more than the first 10 targets.
- (void)testAllCollectedQueriesInSingleTransaction {
  if ([self isTestBaseClass]) return;

  // 50 queries, 11 with one transaction, incrementing from there. Should get first sequence number.
  [self newTestResources];
  _persistence.run("11 queries in a transaction", [&]() {
    for (int i = 0; i < 11; i++) {
      [self addNextQueryInTransaction];
    }
  });
  for (int i = 11; i < 50; i++) {
    [self addNextQuery];
  }
  // We expect to GC the targets from the first transaction, since they account for
  // at least the first 10 of the targets.
  XCTAssertEqual(1 + _initialSequenceNumber, [self sequenceNumberForQueryCount:10]);
  [_persistence shutdown];
}

- (void)testSequenceNumbersWithMutationAndSequentialQueries {
  if ([self isTestBaseClass]) return;

  // Remove a mutated doc reference, marking it as eligible for GC.
  // Then add 50 queries. Should get 10 past initial (9 queries).
  [self newTestResources];
  [self markADocumentEligibleForGC];
  for (int i = 0; i < 50; i++) {
    [self addNextQuery];
  }
  XCTAssertEqual(10 + _initialSequenceNumber, [self sequenceNumberForQueryCount:10]);
  [_persistence shutdown];
}

- (void)testSequenceNumbersWithMutationsInQueries {
  if ([self isTestBaseClass]) return;

  // Add mutated docs, then add one of them to a query target so it doesn't get GC'd.
  // Expect 3 past the initial value: the mutations not part of a query, and two queries
  [self newTestResources];
  FSTDocument *docInQuery = [self nextTestDocument];
  _persistence.run("mark mutations", [&]() {
    // Adding 9 doc keys in a transaction. If we remove one of them, we'll have room for two actual
    // queries.
    [self markDocumentEligibleForGCInTransaction:docInQuery.key];
    for (int i = 0; i < 8; i++) {
      [self markADocumentEligibleForGCInTransaction];
    }
  });
  for (int i = 0; i < 49; i++) {
    [self addNextQuery];
  }
  _persistence.run("query with mutation", [&]() {
    FSTQueryData *queryData = [self addNextQueryInTransaction];
    // This should keep the document from getting GC'd, since it is no longer orphaned.
    [self addDocument:docInQuery.key toTarget:queryData.targetID];
  });

  // This should catch the remaining 8 documents, plus the first two queries we added.
  XCTAssertEqual(3 + _initialSequenceNumber, [self sequenceNumberForQueryCount:10]);
  [_persistence shutdown];
}

- (void)testRemoveQueriesUpThroughSequenceNumber {
  if ([self isTestBaseClass]) return;

  [self newTestResources];
  NSMutableDictionary<NSNumber *, FSTQueryData *> *liveQueries = [[NSMutableDictionary alloc] init];
  for (int i = 0; i < 100; i++) {
    FSTQueryData *queryData = [self addNextQuery];
    // Mark odd queries as live so we can test filtering out live queries.
    if (queryData.targetID % 2 == 1) {
      liveQueries[@(queryData.targetID)] = queryData;
    }
  }
  // GC up through 20th query, which is 20%.
  // Expect to have GC'd 10 targets, since every other target is live
  int removed =
      [self removeQueriesThroughSequenceNumber:20 + _initialSequenceNumber liveQueries:liveQueries];
  XCTAssertEqual(10, removed);
  // Make sure we removed the even targets with targetID <= 20.
  _persistence.run("verify remaining targets are > 20 or odd", [&]() {
    [_queryCache enumerateTargetsUsingBlock:^(FSTQueryData *queryData, BOOL *stop) {
      XCTAssertTrue(queryData.targetID > 20 || queryData.targetID % 2 == 1);
    }];
  });
  [_persistence shutdown];
}

- (void)testRemoveOrphanedDocuments {
  if ([self isTestBaseClass]) return;

  [self newTestResources];
  // Track documents we expect to be retained so we can verify post-GC.
  // This will contain documents associated with targets that survive GC, as well
  // as any documents with pending mutations.
  std::unordered_set<DocumentKey, DocumentKeyHash> expectedRetained;
  // we add two mutations later, for now track them in an array.
  NSMutableArray *mutations = [NSMutableArray arrayWithCapacity:2];

  // Add a target and add two documents to it. The documents are expected to be
  // retained, since their membership in the target keeps them alive.
  _persistence.run("add a target and add two documents to it", [&]() {
    // Add two documents to first target, queue a mutation on the second document
    FSTQueryData *queryData = [self addNextQueryInTransaction];
    FSTDocument *doc1 = [self cacheADocumentInTransaction];
    [self addDocument:doc1.key toTarget:queryData.targetID];
    expectedRetained.insert(doc1.key);

    FSTDocument *doc2 = [self cacheADocumentInTransaction];
    [self addDocument:doc2.key toTarget:queryData.targetID];
    expectedRetained.insert(doc2.key);
    [mutations addObject:[self mutationForDocument:doc2.key]];
  });

  // Add a second query and register a third document on it
  _persistence.run("second query", [&]() {
    FSTQueryData *queryData = [self addNextQueryInTransaction];
    FSTDocument *doc3 = [self cacheADocumentInTransaction];
    expectedRetained.insert(doc3.key);
    [self addDocument:doc3.key toTarget:queryData.targetID];
  });

  // cache another document and prepare a mutation on it.
  _persistence.run("queue a mutation", [&]() {
    FSTDocument *doc4 = [self cacheADocumentInTransaction];
    [mutations addObject:[self mutationForDocument:doc4.key]];
    expectedRetained.insert(doc4.key);
  });

  // Insert the mutations. These operations don't have a sequence number, they just
  // serve to keep the mutated documents from being GC'd while the mutations are outstanding.
  _persistence.run("actually register the mutations", [&]() {
    FIRTimestamp *writeTime = [FIRTimestamp timestamp];
    [_mutationQueue addMutationBatchWithWriteTime:writeTime mutations:mutations];
  });

  // Mark 5 documents eligible for GC. This simulates documents that were mutated then ack'd.
  // Since they were ack'd, they are no longer in a mutation queue, and there is nothing keeping
  // them alive.
  std::unordered_set<DocumentKey, DocumentKeyHash> toBeRemoved;
  _persistence.run("add orphaned docs (previously mutated, then ack'd)", [&]() {
    for (int i = 0; i < 5; i++) {
      FSTDocument *doc = [self cacheADocumentInTransaction];
      toBeRemoved.insert(doc.key);
      [self markDocumentEligibleForGCInTransaction:doc.key];
    }
  });

  // We expect only the orphaned documents, those not in a mutation or a target, to be
  // removed.
  // use a large sequence number to remove as much as possible
  int removed = [self removeOrphanedDocumentsThroughSequenceNumber:1000];
  XCTAssertEqual(toBeRemoved.size(), removed);
  _persistence.run("verify", [&]() {
    for (const DocumentKey &key : toBeRemoved) {
      XCTAssertNil([_documentCache entryForKey:key]);
      XCTAssertFalse([_queryCache containsKey:key]);
    }
    for (const DocumentKey &key : expectedRetained) {
      XCTAssertNotNil([_documentCache entryForKey:key], @"Missing document %s",
                      key.ToString().c_str());
    }
  });
  [_persistence shutdown];
}

// TODO(gsoltis): write a test that includes limbo documents

- (void)testRemoveTargetsThenGC {
  if ([self isTestBaseClass]) return;

  // Create 3 targets, add docs to all of them
  // Leave oldest target alone, it is still live
  // Remove newest target
  // Blind write 2 documents
  // Add one of the blind write docs to oldest target (preserves it)
  // Remove some documents from middle target (bumps sequence number)
  // Add some documents from newest target to oldest target (preserves them)
  // Update a doc from middle target
  // Remove middle target
  // Do a blind write
  // GC up to but not including the removal of the middle target
  //
  // Expect:
  // All docs in oldest target are still around
  // One blind write is gone, the first one not added to oldest target
  // Documents removed from middle target are gone, except ones added to oldest target
  // Documents from newest target are gone, except

  [self newTestResources];

  // Through the various steps, track which documents we expect to be removed vs
  // documents we expect to be retained.
  std::unordered_set<DocumentKey, DocumentKeyHash> expectedRetained;
  std::unordered_set<DocumentKey, DocumentKeyHash> expectedRemoved;

  // Add oldest target, 5 documents, and add those documents to the target.
  // This target will not be removed, so all documents that are part of it will
  // be retained.
  FSTQueryData *oldestTarget =
      _persistence.run("Add oldest target and docs", [&]() -> FSTQueryData * {
        FSTQueryData *queryData = [self addNextQueryInTransaction];
        for (int i = 0; i < 5; i++) {
          FSTDocument *doc = [self cacheADocumentInTransaction];
          expectedRetained.insert(doc.key);
          [self addDocument:doc.key toTarget:queryData.targetID];
        }
        return queryData;
      });

  // Add middle target and docs. Some docs will be removed from this target later,
  // which we track here.
  DocumentKeySet middleDocsToRemove;
  // This will be the document in this target that gets an update later
  DocumentKey middleDocToUpdate;
  FSTQueryData *middleTarget =
      _persistence.run("Add middle target and docs", [&]() -> FSTQueryData * {
        FSTQueryData *middleTarget = [self addNextQueryInTransaction];
        // these docs will be removed from this target later, triggering a bump
        // to their sequence numbers. Since they will not be a part of the target, we
        // expect them to be removed.
        for (int i = 0; i < 2; i++) {
          FSTDocument *doc = [self cacheADocumentInTransaction];
          expectedRemoved.insert(doc.key);
          [self addDocument:doc.key toTarget:middleTarget.targetID];
          middleDocsToRemove = middleDocsToRemove.insert(doc.key);
        }
        // these docs stay in this target and only this target. There presence in this
        // target prevents them from being GC'd, so they are also expected to be retained.
        for (int i = 2; i < 4; i++) {
          FSTDocument *doc = [self cacheADocumentInTransaction];
          expectedRetained.insert(doc.key);
          [self addDocument:doc.key toTarget:middleTarget.targetID];
        }
        // This doc stays in this target, but gets updated.
        {
          FSTDocument *doc = [self cacheADocumentInTransaction];
          expectedRetained.insert(doc.key);
          [self addDocument:doc.key toTarget:middleTarget.targetID];
          middleDocToUpdate = doc.key;
        }
        return middleTarget;
      });

  // Add the newest target and add 5 documents to it. Some of those documents will
  // additionally be added to the oldest target, which will cause those documents to
  // be retained. The remaining documents are expected to be removed, since this target
  // will be removed.
  DocumentKeySet newestDocsToAddToOldest;
  _persistence.run("Add newest target and docs", [&]() {
    FSTQueryData *newestTarget = [self addNextQueryInTransaction];
    // These documents are only in this target. They are expected to be removed
    // because this target will also be removed.
    for (int i = 0; i < 3; i++) {
      FSTDocument *doc = [self cacheADocumentInTransaction];
      expectedRemoved.insert(doc.key);
      [self addDocument:doc.key toTarget:newestTarget.targetID];
    }
    // docs to add to the oldest target in addition to this target. They will be retained
    for (int i = 3; i < 5; i++) {
      FSTDocument *doc = [self cacheADocumentInTransaction];
      expectedRetained.insert(doc.key);
      [self addDocument:doc.key toTarget:newestTarget.targetID];
      newestDocsToAddToOldest = newestDocsToAddToOldest.insert(doc.key);
    }
  });

  // 2 doc writes, add one of them to the oldest target.
  _persistence.run("2 doc writes, add one of them to the oldest target", [&]() {
    // write two docs and have them ack'd by the server. can skip mutation queue
    // and set them in document cache. Add potentially orphaned first, also add one
    // doc to a target.
    FSTDocument *doc1 = [self cacheADocumentInTransaction];
    [self markDocumentEligibleForGCInTransaction:doc1.key];
    [self updateTargetInTransaction:oldestTarget];
    [self addDocument:doc1.key toTarget:oldestTarget.targetID];
    // doc1 should be retained by being added to oldestTarget.
    expectedRetained.insert(doc1.key);

    FSTDocument *doc2 = [self cacheADocumentInTransaction];
    [self markDocumentEligibleForGCInTransaction:doc2.key];
    // nothing is keeping doc2 around, it should be removed
    expectedRemoved.insert(doc2.key);
  });

  // Remove some documents from the middle target.
  _persistence.run("Remove some documents from the middle target", [&]() {
    [self updateTargetInTransaction:middleTarget];
    for (const DocumentKey &docKey : middleDocsToRemove) {
      [self removeDocument:docKey fromTarget:middleTarget.targetID];
    }
  });

  // Add a couple docs from the newest target to the oldest (preserves them past the point where
  // newest was removed)
  // upperBound is the sequence number right before middleTarget is updated, then removed.
  ListenSequenceNumber upperBound = _persistence.run(
      "Add a couple docs from the newest target to the oldest", [&]() -> ListenSequenceNumber {
        [self updateTargetInTransaction:oldestTarget];
        for (const DocumentKey &docKey : newestDocsToAddToOldest) {
          [self addDocument:docKey toTarget:oldestTarget.targetID];
        }
        return _persistence.currentSequenceNumber;
      });

  // Update a doc in the middle target
  _persistence.run("Update a doc in the middle target", [&]() {
    FSTTestSnapshotVersion version = 3;
    FSTDocument *doc = [FSTDocument documentWithData:_testValue
                                                 key:middleDocToUpdate
                                             version:testutil::Version(version)
                                   hasLocalMutations:NO];
    [_documentCache addEntry:doc];
    [self updateTargetInTransaction:middleTarget];
  });

  // middleTarget removed here, no update needed

  // Write a doc and get an ack, not part of a target.
  _persistence.run("Write a doc and get an ack, not part of a target", [&]() {
    FSTDocument *doc = [self cacheADocumentInTransaction];
    // Mark it as eligible for GC, but this is after our upper bound for what we will collect.
    [self markDocumentEligibleForGCInTransaction:doc.key];
    // This should be retained, it's too new to get removed.
    expectedRetained.insert(doc.key);
  });

  // Finally, do the garbage collection, up to but not including the removal of middleTarget
  NSDictionary<NSNumber *, FSTQueryData *> *liveQueries =
      @{@(oldestTarget.targetID) : oldestTarget};
  int queriesRemoved = [self removeQueriesThroughSequenceNumber:upperBound liveQueries:liveQueries];
  XCTAssertEqual(1, queriesRemoved, @"Expected to remove newest target");
  int docsRemoved = [self removeOrphanedDocumentsThroughSequenceNumber:upperBound];
  XCTAssertEqual(expectedRemoved.size(), docsRemoved);
  _persistence.run("verify results", [&]() {
    for (const DocumentKey &key : expectedRemoved) {
      XCTAssertNil([_documentCache entryForKey:key], @"Did not expect to find %s in document cache",
                   key.ToString().c_str());
      XCTAssertFalse([_queryCache containsKey:key], @"Did not expect to find %s in queryCache",
                     key.ToString().c_str());
      [self expectSentinelRemoved:key];
    }
    for (const DocumentKey &key : expectedRetained) {
      XCTAssertNotNil([_documentCache entryForKey:key], @"Expected to find %s in document cache",
                      key.ToString().c_str());
    }
  });

  [_persistence shutdown];
}

- (void)testGetsSize {
  if ([self isTestBaseClass]) return;

  [self newTestResources];

  size_t initialSize = [_gc byteSize];

  _persistence.run("fill cache", [&]() {
    // Simulate a bunch of ack'd mutations
    for (int i = 0; i < 50; i++) {
      FSTDocument *doc = [self cacheADocumentInTransaction];
      [self markDocumentEligibleForGCInTransaction:doc.key];
    }
  });

  size_t finalSize = [_gc byteSize];
  XCTAssertGreaterThan(finalSize, initialSize);

  [_persistence shutdown];
}

@end

NS_ASSUME_NONNULL_END