DiskHealthCheckService (venice API)

java.lang.Object
- com.linkedin.venice.service.AbstractVeniceService
- - com.linkedin.davinci.storage.DiskHealthCheckService

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable
```
public class DiskHealthCheckService
extends AbstractVeniceService
```
DiskHealthCheckService will wake up every 10 seconds by default and run a health check in the disk by writing 64KB random data, read them back and verify the content; if there is any error within the process, an in-memory state variable "diskHealthy" will be updated to false; otherwise, "diskHealthy" will be kept as true. If there is a SSD failure, the disk operation could hang forever; in order to report such kind of disk failure, there is a timeout mechanism inside the health status polling API; a total timeout will be decided at the beginning: totalTimeout = Math.max(30 seconds, health check interval + disk operation timeout) we will keep track of the last update time for the in-memory health status variable, if the in-memory status haven't been updated for more than the totalTimeout, we believe the disk operation hang due to disk failure and start reporting unhealthy for this server.

Nested Class Summary
- Nested classes/interfaces inherited from class com.linkedin.venice.service.AbstractVeniceService
  AbstractVeniceService.ServiceState

Field Summary
- Fields inherited from class com.linkedin.venice.service.AbstractVeniceService
  logger, serviceState

Constructor Summary

Constructors
Constructor	Description
`DiskHealthCheckService(boolean serviceEnabled, long healthCheckIntervalMs, long diskOperationTimeout, java.lang.String databasePath, long diskFailServerShutdownTimeMs)`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`java.lang.String`	`getErrorMessage()`
`boolean`	`isDiskHealthy()`
`boolean`	`startInner()`
`void`	`stopInner()`

Methods inherited from class com.linkedin.venice.service.AbstractVeniceService
close, getName, isRunning, start, stop

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - DiskHealthCheckService
```
public DiskHealthCheckService(boolean serviceEnabled,
                              long healthCheckIntervalMs,
                              long diskOperationTimeout,
                              java.lang.String databasePath,
                              long diskFailServerShutdownTimeMs)
```
- Method Detail
  - startInner
```
public boolean startInner()
```
    Specified by:
    
    startInner in class AbstractVeniceService
    
    Returns:
    
    true if the service is completely started, false if it is still starting asynchronously (in this case, it is the implementer's responsibility to set AbstractVeniceService.serviceState to AbstractVeniceService.ServiceState.STARTED upon completion of the async work).
  - isDiskHealthy
```
public boolean isDiskHealthy()
```
  - getErrorMessage
```
public java.lang.String getErrorMessage()
```
  - stopInner
```
public void stopInner()
```
    Specified by:
    
    stopInner in class AbstractVeniceService