A connection pool is a technique used in database management to optimize the use of database connections in applications. It maintains a pool (or cache) of database connections that are reused, rather than creating and closing connections repeatedly. This improves application performance by reducing the overhead associated with opening and closing database connections.
Copy this this 'compile "com.zaxxer:HikariCP:2.7.7' and past in the build.gradle file and run the project
When using Tomcat with a connection pool in a load balancing environment,
a "hang" or slow response could be due to various factors.
Here are some common causes and potential solutions:
- Database Connection Pool Exhaustion
If the connection pool is exhausted and no available connections are left,it can cause threads to wait indefinitely, leading to a "hang."
Solution:
Increase the maximum number of connections in the connection pool.
Monitor and optimize database queries to ensure they are efficient and don't hold connections unnecessarily.
Ensure that connections are properly closed and returned to the pool after use.
In application.yml of tomcat server , you can set the pool properties like:
maximumPoolSize: 50
minimumIdle: 50
Or In context.xml of tomcat server , you can set the pool properties like:
Resource name="jdbc/yourDataSource"
auth="Container"
type="javax.sql.DataSource"
driverClassName="com.mysql.cj.jdbc.Driver"
url="jdbc:mysql://localhost:3306/yourdb"
username="yourusername"
password="yourpassword"
maxTotal="100"
maxIdle="30"
minIdle="10"
maxWaitMillis="10000"/>
- Thread Starvation
If the threads that handle incoming requests are blocked, either by database connections or
other resources, it can lead to a situation where no threads are available to process new requests, causing a hang.
Solution:
Increase the number of available worker threads in Tomcat by adjusting the maxThreads attribute
In application.yml of tomcat server , you can set the pool properties like:
maximumPoolSize: 50
minimumIdle: 50
Or Go to in the server.xml of tomcat server configuration file:
Connector port="8080" protocol="HTTP/1.1"
maxThreads="200" minSpareThreads="25"
connectionTimeout="20000" redirectPort="8443" />
Check for any deadlock situations or blocking operations in your code or database queries.
- Load Balancer Configuration
If you're using a load balancer in front of multiple Tomcat instances, incorrect load balancing
configuration or session stickiness issues could result in uneven distribution of traffic, causing some
instances to become overloaded while others are underutilized.
Solution:
Ensure sticky sessions (also known as session affinity) are correctly configured if needed,
so requests from the same client go to the same server.
Configure the load balancer to distribute traffic evenly across all Tomcat instances.
- Connection Pool Misconfiguration
Sometimes misconfigured connection pool settings can lead to inefficient connection
management, like improper timeouts or maximum wait times, causing delays in obtaining a
connection and eventually leading to a hang.
Solution:
Set appropriate values for maxWaitMillis (maximum time a connection can be borrowed before timing out)
and validationQuery (query to check if the connection is valid before borrowing it).
In application.yml of tomcat server , you can set the pool properties like:
connectionTimeout: 30000 #30 seconds
idleTimeout: 60000*10 #10 min
maxLifetime: 3600000 #1 hours
Or In context.xml of tomcat server , you can set the pool properties like:
Resource name="jdbc/yourDataSource"
auth="Container"
type="javax.sql.DataSource"
driverClassName="com.mysql.cj.jdbc.Driver"
url="jdbc:mysql://localhost:3306/yourdb"
username="yourusername"
password="yourpassword"
maxTotal="50"
maxIdle="20"
minIdle="5"
maxWaitMillis="5000"
validationQuery="SELECT 1" />
- Tomcat Resource Leaks
If connections or resources aren't being cleaned up properly (e.g., connections not closed properly, or thread leaks),
it can eventually cause the system to hang as resources become exhausted.
Solution:
In application.yml of tomcat server , you can set the pool properties like:
connectionTimeout: 30000 #30 seconds
leakDetectionThreshold: 1200000 // 12 min
Or In context.xml of tomcat server , you can set the pool properties like:
Resource name="jdbc/yourDataSource"
logAbandoned="true"
removeAbandoned="true"
removeAbandonedTimeout="60" />
- JVM and Garbage Collection Issues
A misconfigured JVM or garbage collection (GC) behavior can cause performance degradation and potential
hangs, especially under heavy load.
Solution:
Monitor the JVM and GC logs to check for any long GC pauses or other issues that might be causing delays.
Adjust JVM settings for optimal garbage collection tuning, such as adjusting heap sizes or choosing a different
GC strategy like G1GC for better performance in high-load situations.
- Database Connectivity Issues
Ensure there are no network-related issues between Tomcat and the database server. Connection timeouts or network
partitioning could cause hangs if connections are not established correctly.
Solution:
Ensure your database server is reachable and has sufficient resources (e.g., CPU, memory).
Set appropriate timeouts and retry logic for the database connection.
- Application Code Issues
Sometimes, issues in your application code, like deadlocks, infinite loops, or other blocking operations,
can cause the application to hang.
Solution:
Profile the application using a tool like VisualVM or JProfiler to track down slow or blocking operations.
Review your application code to ensure that you are handling resources efficiently and that you don't have blocking
or deadlocking code patterns.
By addressing these potential issues, you can improve the performance and reliability of your
Tomcat-based load-balanced environment and reduce the chances of experiencing hangs or slowdowns.
