add auto checkpoint to limit `sqlite-wal` file's size

YYCache/YYKVStorage.m

@@ -135,6 +135,12 @@ static NSString *const kTrashDirectoryName = @"trash";
     return [self _dbExecute:sql];
 }
 
+- (void)_dbCheckpoint {
+    if (![self _dbIsReady]) return;
+    // Cause a checkpoint to occur, merge `sqlite-wal` file to `sqlite` file.
+    sqlite3_wal_checkpoint(_db, NULL);
+}
+
 - (BOOL)_dbExecute:(NSString *)sql {
     if (sql.length == 0) return NO;
     if (![self _dbIsReady]) return NO;
@@ -777,7 +783,10 @@ static NSString *const kTrashDirectoryName = @"trash";
     
     switch (_type) {
         case YYKVStorageTypeSQLite: {
-            return [self _dbDeleteItemsWithSizeLargerThan:size];
+            if ([self _dbDeleteItemsWithSizeLargerThan:size]) {
+                [self _dbCheckpoint];
+                return YES;
+            }
         } break;
         case YYKVStorageTypeFile:
         case YYKVStorageTypeMixed: {
@@ -785,7 +794,10 @@ static NSString *const kTrashDirectoryName = @"trash";
             for (NSString *name in filenames) {
                 [self _fileDeleteWithName:name];
             }
-            return [self _dbDeleteItemsWithSizeLargerThan:size];
+            if ([self _dbDeleteItemsWithSizeLargerThan:size]) {
+                [self _dbCheckpoint];
+                return YES;
+            }
         } break;
     }
     return NO;
@@ -797,7 +809,10 @@ static NSString *const kTrashDirectoryName = @"trash";
     
     switch (_type) {
         case YYKVStorageTypeSQLite: {
-            return [self _dbDeleteItemsWithTimeEarlierThan:time];
+            if ([self _dbDeleteItemsWithTimeEarlierThan:time]) {
+                [self _dbCheckpoint];
+                return YES;
+            }
         } break;
         case YYKVStorageTypeFile:
         case YYKVStorageTypeMixed: {
@@ -805,7 +820,10 @@ static NSString *const kTrashDirectoryName = @"trash";
             for (NSString *name in filenames) {
                 [self _fileDeleteWithName:name];
             }
-            return [self _dbDeleteItemsWithTimeEarlierThan:time];
+            if ([self _dbDeleteItemsWithTimeEarlierThan:time]) {
+                [self _dbCheckpoint];
+                return NO;
+            }
         } break;
     }
     return NO;
@@ -837,6 +855,7 @@ static NSString *const kTrashDirectoryName = @"trash";
             if (!suc) break;
         }
     } while (total > maxSize && items.count > 0 && suc);
+    if (suc) [self _dbCheckpoint];
     return suc;
 }
 
@@ -866,6 +885,7 @@ static NSString *const kTrashDirectoryName = @"trash";
             if (!suc) break;
         }
     } while (total > maxCount && items.count > 0 && suc);
+    if (suc) [self _dbCheckpoint];
     return suc;
 }
 
@@ -904,6 +924,7 @@ static NSString *const kTrashDirectoryName = @"trash";
             }
             if (progress) progress(total - left, total);
         } while (left > 0 && items.count > 0 && suc);
+        if (suc) [self _dbCheckpoint];
         if (end) end(!suc);
     }
 }