o.h.engine.jdbc.spi.SqlExceptionHelper : FATAL: query_wait_timeout - spring-boot

Question

I am using SpringBoot application with PostgreSQL as database, I am doing Load Testing from Jmeter, Database is hosted in azure, when I try to hit 150 Rest request to Single API or endpoint parallelly/concurrently, I am getting below error but with 100 request it works successfully.
ERROR:
2022-12-21 17:29:43.000 WARN 1 --- [http-nio-8080-exec-60] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 0, SQLState: 08P01
2022-12-21 17:29:43.000 ERROR 1 --- [http-nio-8080-exec-60] o.h.engine.jdbc.spi.SqlExceptionHelper : FATAL: query_wait_timeout
2022-12-21 17:29:43.000 WARN 1 --- [http-nio-8080-exec-60] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 0, SQLState: 08006
2022-12-21 17:29:43.001 ERROR 1 --- [http-nio-8080-exec-60] o.h.engine.jdbc.spi.SqlExceptionHelper : An I/O error occurred while sending to the backend.
2022-12-21 17:29:43.090 WARN 1 --- [http-nio-8080-exec-61] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 0, SQLState: 08P01
2022-12-21 17:29:43.090 ERROR 1 --- [http-nio-8080-exec-61] o.h.engine.jdbc.spi.SqlExceptionHelper : FATAL: query_wait_timeout
I want to improve the performance of the application in short solve the above error when we auto-scale our application with two instances, 150 request are passed but when we run with a single instance, it gives the above error, I want to understand
whether it is a memory issue or a db issue?
How to resolve it ?`

Answer 1

As per documentation:
query_wait_timeout
Maximum time queries are allowed to spend waiting for execution. If the query is not assigned to a server during that time, the client is disconnected. 0 disables. If this is disabled, clients will be queued indefinitely. [seconds]
This setting is used to prevent unresponsive servers from grabbing up connections. It also helps when the server is down or rejects connections for any reason.
Default: 120
Most probably all the connections in the PostgreSQL connection pool are busy and your application fails to obtain one within the bounds of pre-defined timeout of 2 minutes.
The options are in:
Increase connection pool size
Increase the aforementioned timeout
Check Postgresql slow queries logs and execution plans for these queries
Test the database in isolation using JDBC Request sampler
Use a profiler tool like JProfiler or YourKit to see whether the long processing is somewhere in your application source code.