Change write groups to use transactions (#912)

* Start work on leveldb transactions

* Style

* Working API. Not plumbed in yet

* Move files into correct place

* Wrangling file locations and associations

* Tests pass

* Add some comments

* style

* Fix copyright

* Rewrite iterator internals to handle deletion-while-iterating. Also add tests for same

* Switch to strings instead of slices

* Style

* More style fixes

* Start switching writegroup over

* Swap out write group tracking for transaction usage

* Style

* Response to feedback before updating docs

* Style

* Add comment

* Initialize version_

* Satisfy the linter

* Start switching writegroup over

* Swap out write group tracking for transaction usage

* Style

* Checkpoint before implementing BatchDescription

* Style

* Everything passing

* Drop unused function

* Style

* Renaming

* Style

* Add log line

* Style

* Add debug log line for commits, drop unused BatchDescription

1 files changed, 25 insertions, 33 deletions

diff --git a/Firestore/Source/Local/FSTLevelDBMigrations.mm b/Firestore/Source/Local/FSTLevelDBMigrations.mm
index 7595c53..7f521d1 100644
--- a/Firestore/Source/Local/FSTLevelDBMigrations.mm
+++ b/Firestore/Source/Local/FSTLevelDBMigrations.mm
@@ -16,13 +16,12 @@
 
 #include "Firestore/Source/Local/FSTLevelDBMigrations.h"
 
+#include <absl/strings/match.h>
 #include "leveldb/write_batch.h"
 
 #import "Firestore/Protos/objc/firestore/local/Target.pbobjc.h"
-#import "Firestore/Source/Local/FSTLevelDB.h"
 #import "Firestore/Source/Local/FSTLevelDBKey.h"
 #import "Firestore/Source/Local/FSTLevelDBQueryCache.h"
-#import "Firestore/Source/Local/FSTWriteGroup.h"
 #import "Firestore/Source/Util/FSTAssert.h"
 
 NS_ASSUME_NONNULL_BEGIN
@@ -30,6 +29,7 @@ NS_ASSUME_NONNULL_BEGIN
 // Current version of the schema defined in this file.
 static FSTLevelDBSchemaVersion kSchemaVersion = 2;
 
+using firebase::firestore::local::LevelDbTransaction;
 using leveldb::DB;
 using leveldb::Iterator;
 using leveldb::Status;
@@ -38,24 +38,24 @@ using leveldb::WriteOptions;
 
 /**
  * Ensures that the global singleton target metadata row exists in LevelDB.
- * @param db The db in which to require the row.
  */
-static void EnsureTargetGlobal(std::shared_ptr<DB> db, FSTWriteGroup *group) {
-  FSTPBTargetGlobal *targetGlobal = [FSTLevelDBQueryCache readTargetMetadataFromDB:db];
+static void EnsureTargetGlobal(LevelDbTransaction *transaction) {
+  FSTPBTargetGlobal *targetGlobal =
+      [FSTLevelDBQueryCache readTargetMetadataWithTransaction:transaction];
   if (!targetGlobal) {
-    [group setMessage:[FSTPBTargetGlobal message] forKey:[FSTLevelDBTargetGlobalKey key]];
+    transaction->Put([FSTLevelDBTargetGlobalKey key], [FSTPBTargetGlobal message]);
   }
 }
 
 /**
  * Save the given version number as the current version of the schema of the database.
  * @param version The version to save
- * @param group The transaction in which to save the new version number
+ * @param transaction The transaction in which to save the new version number
  */
-static void SaveVersion(FSTLevelDBSchemaVersion version, FSTWriteGroup *group) {
+static void SaveVersion(FSTLevelDBSchemaVersion version, LevelDbTransaction *transaction) {
   std::string key = [FSTLevelDBVersionKey key];
   std::string version_string = std::to_string(version);
-  [group setData:version_string forKey:key];
+  transaction->Put(key, version_string);
 }
 
 /**
@@ -65,30 +65,32 @@ static void SaveVersion(FSTLevelDBSchemaVersion version, FSTWriteGroup *group) {
  *
  * It assumes the metadata has already been written and is able to be read in this transaction.
  */
-static void AddTargetCount(std::shared_ptr<DB> db, FSTWriteGroup *group) {
-  std::unique_ptr<Iterator> it(db->NewIterator([FSTLevelDB standardReadOptions]));
-  Slice start_key = [FSTLevelDBTargetKey keyPrefix];
+static void AddTargetCount(LevelDbTransaction *transaction) {
+  std::unique_ptr<LevelDbTransaction::Iterator> it(transaction->NewIterator());
+  std::string start_key = [FSTLevelDBTargetKey keyPrefix];
   it->Seek(start_key);
 
   int32_t count = 0;
-  while (it->Valid() && it->key().starts_with(start_key)) {
+  while (it->Valid() && absl::StartsWith(it->key(), start_key)) {
     count++;
     it->Next();
   }
 
-  FSTPBTargetGlobal *targetGlobal = [FSTLevelDBQueryCache readTargetMetadataFromDB:db];
+  FSTPBTargetGlobal *targetGlobal =
+      [FSTLevelDBQueryCache readTargetMetadataWithTransaction:transaction];
   FSTCAssert(targetGlobal != nil,
              @"We should have a metadata row as it was added in an earlier migration");
   targetGlobal.targetCount = count;
-  [group setMessage:targetGlobal forKey:[FSTLevelDBTargetGlobalKey key]];
+  transaction->Put([FSTLevelDBTargetGlobalKey key], targetGlobal);
 }
 
 @implementation FSTLevelDBMigrations
 
-+ (FSTLevelDBSchemaVersion)schemaVersionForDB:(std::shared_ptr<DB>)db {
++ (FSTLevelDBSchemaVersion)schemaVersionWithTransaction:
+    (firebase::firestore::local::LevelDbTransaction *)transaction {
   std::string key = [FSTLevelDBVersionKey key];
   std::string version_string;
-  Status status = db->Get([FSTLevelDB standardReadOptions], key, &version_string);
+  Status status = transaction->Get(key, &version_string);
   if (status.IsNotFound()) {
     return 0;
   } else {
@@ -96,34 +98,24 @@ static void AddTargetCount(std::shared_ptr<DB> db, FSTWriteGroup *group) {
   }
 }
 
-+ (void)runMigrationsOnDB:(std::shared_ptr<DB>)db {
-  FSTWriteGroup *group = [FSTWriteGroup groupWithAction:@"Migrations"];
-  FSTLevelDBSchemaVersion currentVersion = [self schemaVersionForDB:db];
++ (void)runMigrationsWithTransaction:(firebase::firestore::local::LevelDbTransaction *)transaction {
+  FSTLevelDBSchemaVersion currentVersion = [self schemaVersionWithTransaction:transaction];
   // Each case in this switch statement intentionally falls through. This lets us
   // start at the current schema version and apply any migrations that have not yet
   // been applied, to bring us up to current, as defined by the kSchemaVersion constant.
   switch (currentVersion) {
     case 0:
-      EnsureTargetGlobal(db, group);
+      EnsureTargetGlobal(transaction);
       // Fallthrough
     case 1:
-      // We need to make sure we have metadata, since we're going to read and modify it
-      // in this migration. Commit the current transaction and start a new one. Since we're
-      // committing, we need to save a version. It's safe to save this one, if we crash
-      // after saving we'll resume from this step when we try to migrate.
-      SaveVersion(1, group);
-      [group writeToDB:db];
-      group = [FSTWriteGroup groupWithAction:@"Migrations"];
-      AddTargetCount(db, group);
+      // We're now guaranteed that the target global exists. We can safely add a count to it.
+      AddTargetCount(transaction);
       // Fallthrough
     default:
       if (currentVersion < kSchemaVersion) {
-        SaveVersion(kSchemaVersion, group);
+        SaveVersion(kSchemaVersion, transaction);
       }
   }
-  if (!group.isEmpty) {
-    [group writeToDB:db];
-  }
 }
 
 @end