Improve RocksDB interface

- Add keyMayExist methods
- Add file deletion methods
- Fix spelling mistakes

Code/RocksDB.h

@@ -349,7 +349,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  Returns the object for the given key.
 
- @peram aKey The key for object.
+ @param aKey The key for object.
  @param error If an error occurs, upon return contains an `NSError` object that describes the problem.
  @return The object for the given key.
  */
@@ -358,7 +358,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  Returns the object for the given key.
 
- @peram aKey The key for object.
+ @param aKey The key for object.
  @param error If an error occurs, upon return contains an `NSError` object that describes the problem.
  @param readOptions A block with a `RocksDBReadOptions` instance for configuring this read operation.
  @return The object for the given key.
@@ -369,6 +369,35 @@ NS_ASSUME_NONNULL_BEGIN
 					readOptions:(nullable void (^)(RocksDBReadOptions *readOptions))readOptions
 						  error:(NSError * _Nullable *)error;
 
+/**
+ If the key definitely does not exist in the database, then this method
+ returns false, else true.
+
+ This check is potentially lighter-weight than invoking dataForKey. One way
+ to make this lighter weight is to avoid doing any IOs.
+
+ @param aKey The key for object to check.
+ @param value out parameter if a value is found in block-cache.
+ @return The object for the given key.
+ */
+- (BOOL)keyMayExist:(NSData *)aKey value:(NSString * _Nullable *_Nullable)value;
+
+/**
+ If the key definitely does not exist in the database, then this method
+ returns false, else true.
+
+ This check is potentially lighter-weight than invoking dataForKey. One way
+ to make this lighter weight is to avoid doing any IOs.
+
+ @param aKey The key for object to check.
+ @param readOptions `RocksDBReadOptions` instance for configuring this read operation.
+ @param value out parameter if a value is found in block-cache.
+ @return The object for the given key.
+ */
+- (BOOL)keyMayExist:(NSData *)aKey
+        readOptions:(nullable void (^)(RocksDBReadOptions *readOptions))readOptions
+              value:(NSString * _Nullable *_Nullable)value;
+
 @end
 
 #pragma mark - Delete operations
@@ -382,7 +411,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  Deletes the object for the given key.
 
- @peram aKey The key to delete.
+ @param aKey The key to delete.
  @param error If an error occurs, upon return contains an `NSError` object that describes the problem.
  @return `YES` if the operation succeeded, `NO` otherwise
  */
@@ -391,7 +420,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  Deletes the object for the given key.
 
- @peram aKey The key to delete.
+ @param aKey The key to delete.
  @param error If an error occurs, upon return contains an `NSError` object that describes the problem.
  @param writeOptions A block with a `RocksDBWriteOptions` instance for configuring this delete operation.
  @return `YES` if the operation succeeded, `NO` otherwise
@@ -571,4 +600,49 @@ NS_ASSUME_NONNULL_BEGIN
 
 @end
 
+#pragma mark - File Deletions
+
+@interface RocksDB (FileDeletion)
+
+///--------------------------------
+/// @name File Deletions
+///--------------------------------
+
+/**
+ Prevent file deletions. Compactions will continue to occur,
+ but no obsolete files will be deleted. Calling this multiple
+ times have the same effect as calling it once.
+ */
+- (void)disableFileDeletions;
+
+/**
+ Allow compactions to delete obsolete files.
+ If force == true, the call to EnableFileDeletions()
+ will guarantee that file deletions are enabled after
+ the call, even if DisableFileDeletions() was called
+ multiple times before.
+
+ If force == false, EnableFileDeletions will only
+ enable file deletion after it's been called at least
+ as many times as DisableFileDeletions(), enabling
+ the two methods to be called by two threads
+ concurrently without synchronization
+ -- i.e., file deletions will be enabled only after both
+ threads call EnableFileDeletions()
+
+ @param force boolean value described above.
+ */
+- (void)enableFileDelections:(BOOL)force;
+
+/**
+ Delete the file name from the db directory and update the internal state to
+ reflect that. Supports deletion of sst and log files only. 'name' must be
+ path relative to the db directory. eg. 000001.sst, /archive/000003.log
+ 
+ @param name the file name
+ */
+- (void)deleteFile:(NSString *)name;
+
+@end
+
 NS_ASSUME_NONNULL_END

Code/RocksDB.mm

@@ -327,7 +327,7 @@ - (void)setDefaultReadOptions:(void (^)(RocksDBReadOptions *))readOptionsBlock w
 
 #if !(defined(ROCKSDB_LITE) && defined(TARGET_OS_IPHONE))
 
-#pragma mark - Peroperties
+#pragma mark - Properties
 
 - (NSString *)valueForProperty:(RocksDBProperty)property
 {
@@ -455,6 +455,32 @@ - (NSData *)dataForKey:(NSData *)aKey
 	return DataFromSlice(rocksdb::Slice(value));
 }
 
+- (BOOL)keyMayExist:(NSData *)aKey value:(NSString * _Nullable *)value
+{
+    return [self keyMayExist:aKey readOptions:nil value:value];
+}
+
+- (BOOL)keyMayExist:(NSData *)aKey
+        readOptions:(nullable void (^)(RocksDBReadOptions *readOptions))readOptionsBlock
+              value:(NSString * _Nullable *)value
+{
+    RocksDBReadOptions *readOptions = [_readOptions copy];
+    if (readOptionsBlock) {
+        readOptionsBlock(readOptions);
+    }
+
+    bool found = NO;
+    std::string stringValue;
+    _db->KeyMayExist(readOptions.options,
+                     _columnFamily,
+                     SliceFromData(aKey),
+                     &stringValue,
+                     &found);
+
+    *value = [NSString stringWithUTF8String:stringValue.c_str()];
+    return found;
+}
+
 #pragma mark - Delete Operations
 
 - (BOOL)deleteDataForKey:(NSData *)aKey error:(NSError * __autoreleasing *)error
@@ -637,4 +663,21 @@ - (BOOL)compactRange:(RocksDBKeyRange *)range
 	return YES;
 }
 
+#pragma mark - File Deletions
+
+- (void)disableFileDeletions
+{
+    _db->DisableFileDeletions();
+}
+
+- (void)enableFileDelections:(BOOL)force
+{
+    _db->EnableFileDeletions(force);
+}
+
+- (void)deleteFile:(NSString *)name
+{
+    _db->DeleteFile(name.UTF8String);
+}
+
 @end