openGauss Common JDBC Parameters
Tags: opengauss
Published: 2023-03-16 08:10:34

targetServerType
Principle: If the value is master, JDBC attempts to connect to the IP addresses configured in the string in sequence until the primary node in the cluster is connected.

If the value is slave, JDBC attempts to connect to the IP addresses configured in the string in sequence until the standby node in the cluster is connected. The query statement is select local_role, db_state from pg_stat_get_stream_replications();.

Suggestion: You are advised to set this parameter to master for services with write operations to ensure that the primary node can be properly connected after a primary/standby switchover. However, if the standby node is not completely promoted to primary during the primary/standby switchover, the connection cannot be established. As a result, service statements cannot be executed.

hostRecheckSeconds
Principle: Specifies the period during which the DN list stored in JDBC remains trusted. Within this period, the DN list is directly read from the host addresses stored in JDBC. After that (or the primary node fails to be connected within the specified period), the node status in the DN list is updated and other IP addresses are connected.

Suggestion: The default value is 10s. You are advised to adjust the value based on service requirements. This parameter is used together with the targetServerType parameter.

allowReadOnly
Principle: Checks whether the transaction access mode can be modified through setReadOnly. If the value is true, the transaction access mode can be modified. If the value is false, the transaction access mode cannot be modified through this interface. To modify the transaction access mode, execute SET SESSION CHARACTERISTICS AS TRANSACTION + READ ONLY / READ WEITE.

Suggestion: The default value true is recommended.

fetchsize
Principle: After fetchsize is set to n and the database server executes a query, JDBC communicates with the server when the invoker executes resultset.next(), fetches n pieces of data to the JDBC client, and returns the first piece of data to the invoker. When the invoker fetches the (n+1)th data record, the invoker fetches data from the database server again.

Function: This prevents the database from transmitting all results to the client at a time, which exhausts the memory resources of the client.

Suggestion: You are advised to set this parameter based on the amount of data queried by services and the memory of the client. When setting fetchsize, disable automatic commit (autocommit=false). Otherwise, the setting of fetchsize does not take effect.

defaultRowFetchSize
Function: The default value of fetchsize is 0. Setting defaultRowFetchSize will change the default value of fetchsize.

batchMode
Function: This parameter specifies whether to connect the database in batch mode. The default value is on. After the function is enabled, the batch update performance is improved, and the return value is also batch updated. For example, if three data records are inserted in batches, the return value is [3,0,0] when the function is enabled, and the return value is [1,1,1] when the function is disabled.

Suggestion: If the service framework (such as hibernate) checks the return value during batch update, you can set this parameter to solve the problem.

loginTimeout
Function: Controls the time for establishing a connection with the database. The time includes connection timeout and socket timeout. If the time elapsed exceeds the threshold, the connection exits. The calculation formula is as follows: loginTimeout = connectiontimeout x Number of nodes + Connection authentication time + Initialization statement execution time.

Suggestion: After this parameter is set, an asynchronous thread is started each time a connection is established. If there are a large number of connections, the pressure on the client may increase. If this parameter needs to be set, you are advised to set it to 3 x connectTimeout in centralized deployment to prevent connection failures when the network is abnormal and the third IP address is the IP address of the primary node.

 NOTICE: After this parameter is set, for multiple IP addresses, the value of this parameter is the time for attempting to connect to all the IP addresses. If this parameter is set to a small value, the subsequent IP addresses may fail to be connected. For example, if three IP addresses are set, logintimeout is set to 5s, and it takes 5s to connect to the first two IP addresses, the third IP address cannot be connected. In the centralized deployment environment, the last IP address is the IP address of the primary node. As a result, the automatic search for the primary node may fail.

cancelSignalTimeout
Function: Cancel messages may cause a block. This parameter controls connectTimeout and socketTimeout in a cancel message, in seconds. It is used to prevent timeout detection from being performed when the connection is canceled due to timeout.

Suggestion: The default value is 10s. You are advised to adjust the value based on service requirements.

connectTimeout
Function: Controls the socket timeout threshold during connection setup. In this case, this timeout threshold is the time when the JDBC connects to the database through the socket, not the time when the connection object is returned. If the time elapsed exceeds the threshold, JDBC searches for the next IP address.

Suggestion: This parameter determines the maximum timeout interval for establishing a TCP connection on each node. If a network fault occurs on a node, JDBC attempts to connect to the node until the time specified by connectTimeout elapses, and then attempts to connect to the next node. Considering the network jitter and delay, you are advised to set this parameter to 3s.

socketTimeout
Function: Controls the timeout threshold of socket operations. If the time of executing service statements or reading data streams from the network exceeds the threshold (that is, when the statement execution time exceeds the specified threshold and no data is returned), the connection is interrupted.

Suggestion: This parameter specifies the maximum execution time of a single SQL statement. If the execution time of a single SQL statement exceeds the value of this parameter, an error is reported and the statement exits. You are advised to set this parameter based on service characteristics.

autosave
Function: If the value is always, you can set a savepoint before each statement in a transaction. If an error is reported during statement execution in a transaction, the system returns to the latest savepoint. In this way, subsequent statements in the transaction can be properly executed and committed.

Suggestion: You are not advised to set this parameter because the performance deteriorates severely.

currentSchema
Function: Specifies the schema of the current connection. If this parameter is not set, the default schema is the username used for the connection.

Suggestion: You are advised to set this parameter to the schema where the service data is located.

prepareThreshold
Function: The default value is 5. If an SQL statement is executed for multiple consecutive times in a session and the number of execution times specified by prepareThreshold is reached, JDBC does not send the PARSE command to the SQL statement but caches the SQL statement to improve the execution speed.

Suggestion: The default value is 5. Adjust the value based on service requirements.

preparedStatementCacheQueries
Function: Specifies the number of queries cached in each connection. The default value is 256. If more than 256 different queries are used in the prepareStatement() call, the least recently used query cache will be discarded.

Suggestion: The default value is 256. Adjust the value based on service requirements. This parameter is used together with prepareThreshold.

blobMode
Function: Sets the setBinaryStream method to assign values to different types of data. The value on indicates that values are assigned to BLOB data. The value off indicates that values are assigned to bytea data. The default value is on. For example, you can assign values to parameters in the preparestatement and callablestatement objects.

Suggestion: The default value is true.

setAutocommit
Function: If the value is true, a transaction is automatically started when each statement is executed. After the execution is complete, the transaction is automatically committed. That is, each statement is a transaction. If the value is false, a transaction is automatically started. However, you need to manually commit the transaction.

Suggestion: Adjust the value based on service characteristics. If autocommit needs to be disabled for performance or other purposes, the application must ensure that transactions can be committed. For example, explicitly commit translations after specifying service SQL statements. Particularly, ensure that all transactions are committed before the client exits.