MongoDB secondary connection support

Author: PicoCreator

src/main/java/picoded/dstack/mongodb/MongoDBStack.java

@@ -52,7 +52,7 @@ public class MongoDBStack extends CoreStack {
 		"	\"w\":\"majority\"," + //
 		"	\"retryWrites\":\"true\"," + //
 		"	\"retryReads\":\"true\"," + //
-		"	\"maxPoolSize\":10," + //
+		"	\"maxPoolSize\":20," + //
 		"	\"compressors\":\"zstd\"" + //
 		"}";
 
@@ -134,9 +134,6 @@ public static String getFullConnectionURL_primary(GenericConvertMap<String, Obje
 					+ "is highly recommended for replica clusters to ensure read after write consistency.");
 		}
 
-		// In the future we may want to support opt_map
-		// GenericConvertMap<String,Object> optMap = config.getGenericConvertStringMap("opt_map", "{}");
-		
 		// Lets build the auth str
 		String authStr = "";
 		if (user != null && pass != null) {
@@ -180,10 +177,10 @@ public static String getFullConnectionURL_secondary(GenericConvertMap<String, Ob
 		String host = config.getString("host", "localhost");
 		int port = config.getInt("port", 27017);
 
-		// Hanlding of option string
+		// Hanlding of option string, default sec_opt uses `secondaryPreferred`
 		GenericConvertMap<String, Object> optMap = new GenericConvertHashMap<>();
 		optMap.putAll(config.getGenericConvertStringMap("opt", defaultOptJson));
-		optMap.putAll(config.getGenericConvertStringMap("sec_opt", "{}"));
+		optMap.putAll(config.getGenericConvertStringMap("sec_opt", "{ \"readPreference\":\"secondaryPreferred\" }"));
 
 		// The opt string overwrite
 		String optStr = config.getString("sec_opt_str", mapToOptStr(optMap));
@@ -204,13 +201,10 @@ public static String getFullConnectionURL_secondary(GenericConvertMap<String, Ob
 			LOGGER
 				.warning("MongoDB is configured without readConcernLevel for the secondary connection, "
 					+ "this is alright for a single node, but `readConcernLevel=linearizable`"
-					+ "or `readPreference=master&readConcernLevel=majority`"
+					+ "or `readPreference=secondaryPreferred&readConcernLevel=majority`"
 					+ "is highly recommended for replica clusters to ensure read after write consistency.");
 		}
 
-		// In the future we may want to support opt_map
-		// GenericConvertMap<String,Object> optMap = config.getGenericConvertStringMap("opt_map", "{}");
-		
 		// Lets build the auth str
 		String authStr = "";
 		if (user != null && pass != null) {

src/main/java/picoded/dstack/mongodb/MongoDB_DataObjectMap.java

@@ -60,6 +60,10 @@ public class MongoDB_DataObjectMap extends Core_DataObjectMap {
 	/** MongoDB instance representing the backend connection */
 	MongoCollection<Document> collection = null;
 
+	/** Secondary connection, and its applicable mode */
+	MongoCollection<Document> sec_collection = null;
+	String sec_mode = null;
+	
 	/**
 	 * Constructor, with name constructor
 	 * 
@@ -69,6 +73,12 @@ public class MongoDB_DataObjectMap extends Core_DataObjectMap {
 	public MongoDB_DataObjectMap(MongoDBStack inStack, String name) {
 		super();
 		collection = inStack.db_conn.getCollection(name);
+		
+		// Get the secondary collection if applicable
+		if (inStack.sec_db_conn != null) {
+			sec_collection = inStack.sec_db_conn.getCollection(name);
+			sec_mode = inStack.sec_mode;
+		}
 	}
 
 	//--------------------------------------------------------------------------
@@ -418,7 +428,28 @@ public String[] query_id(Query queryClause, String orderByStr, int offset, int l
 		}
 
 		// Lets fetch the data, for the various _oid
-		FindIterable<Document> search = collection.find(bsonFilter);
+		FindIterable<Document> search = null;
+		
+		// Chose the respective serach mode
+		if (sec_mode == null) {
+			// NULL safety
+			search = collection.find(bsonFilter);
+		} else if (sec_mode.equals("LIKE")) {
+			// Use secondary connection for LIKE query
+			if (queryClause.toSqlString().toUpperCase().indexOf("LIKE") > 0) {
+				search = sec_collection.find(bsonFilter);
+			}
+		} else if (sec_mode.equals("QUERY")) {
+			// Use secondary for all queries
+			search = sec_collection.find(bsonFilter);
+		}
+		
+		// Fallback to main collection query
+		if (search == null) {
+			search = collection.find(bsonFilter);
+		}
+		
+		// Apply the projection, to only fetch _oid
 		search = search.projection(Projections.include("_oid"));
 
 		// Build the orderBy clause