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db_pool_suspension

ABSTRACT

In the context of connection pools, like HikariCP, refers to a feature or mechanism that allows the pool to temporarily stop serving new connections without immediately shutting down the pool or discarding all existing connections

This can be useful during maintenance or when there are temporary issues with the database that need to be resolved.

Purpose​

  1. Temporary Halt

    • Prevent new transactions or operations from starting
    • Ongoing transactions are allowed to complete.

  2. Graceful Maintenance

    • Controlled maintenance
    • Recovery process without disrupting active connections
    • For example, during a database restart, the pool can be suspended to avoid connection failures until the database is back online.

How Pool Suspension Works​

  1. No New Connections

Any request to borrow a new connection will either wait or fail immediately (depending on pool configuration)

  1. Existing Connections Remain Active

    • Existing connections that are already borrowed from the pool remain active and continue to function normally
    • Allows ongoing transactions to complete without interruption

  2. Reactivation

    • Once the underlying issue is resolved, or the maintenance is complete, the pool can be "resumed," allowing new connections to be borrowed again.

Usage Scenarios​

  1. Database Restart or Maintenance
    • Planned or unplanned database restarts
    • Suspending the pool prevents a flood of connection attempts that would otherwise fail and cause exceptions
  2. Graceful Degradation
    • In a microservices environment, when a service detects that a dependent database is down
    • Dependent DB down > suspend its connection pool to prevent unnecessary load and quickly fail fast, allowing the service to degrade gracefull
  3. Resource Constraints
    • In case of temporary resource constraints (e.g., high CPU or memory usage), suspending the pool can help prevent further load on the database or application server

Integration with HikariCP​

HikariCP and Pool Suspension: HikariCP, a high-performance JDBC connection pool, does not natively support a "suspend" feature in its basic configuration. However, you can implement similar behavior by combining the following configurations and application-level controls: Set maximumPoolSize to zero: Temporarily set the maximum pool size to zero to prevent new connections from being created. This effectively "suspends" new connections but does not impact active ones. Connection Timeout Adjustments: Increase the connectionTimeout to a high value to avoid immediate failures when the pool is suspended. Custom Implementation for Suspension in HikariCP:

While HikariCP does not provide built-in pool suspension, you can implement your suspension mechanism in your application logic:

References

  • ChatGPT