AdaptiveFetchSchedule

All Implemented Interfaces:

ai.platon.pulsar.common.config.Parameterized , ai.platon.pulsar.crawl.schedule.FetchSchedule
```
public class AdaptiveFetchSchedule
extends AbstractFetchSchedule
                    
```
This class implements an adaptive re-fetch algorithm. This works as follows:
- for pages that has changed since the last fetchTime, decrease their fetchInterval by a factor of DEC_FACTOR (default value is 0.2f).
- for pages that haven't changed since the last fetchTime, increase their fetchInterval by a factor of INC_FACTOR (default value is 0.2f).<br></br> If SYNC_DELTA property is true, then:
- calculate a delta = fetchTime - modifiedTime
- try to synchronize with the time of change, by shifting the next fetchTime by a fraction of the difference between the last modification time and the last fetch time. I.e. the next fetch time will be set to fetchTime + fetchInterval - delta * SYNC_DELTA_RATE
- if the adjusted fetch interval is bigger than the delta, then fetchInterval = delta.
- the minimum value of fetchInterval may not be smaller than MIN_INTERVAL (default is 1 minute).
- the maximum value of fetchInterval may not be bigger than MAX_INTERVAL (default is 365 days).
NOTE: values of DEC_FACTOR and INC_FACTOR higher than 0.4f may destabilize the algorithm, so that the fetch interval either increases or decreases infinitely, with little relevance to the page changes. Please use . method to test the values before applying them in a production system.

Field Summary

Fields
Modifier and Type	Field	Description
`private final Duration`	`maxFetchInterval`
`private final ImmutableConfig`	`conf`
`private final MiscMessageWriter`	`messageWriter`

Constructor Summary

Constructors
Constructor	Description
`AdaptiveFetchSchedule(ImmutableConfig conf, MiscMessageWriter messageWriter)`

Method Summary

Modifier and Type	Method	Description
`Duration`	`getMaxFetchInterval()`
`final ImmutableConfig`	`getConf()`
`final MiscMessageWriter`	`getMessageWriter()`
`Params`	`getParams()`
`Unit`	`setFetchSchedule(WebPage page, ModifyInfo m)`	Sets the `fetchInterval` and `fetchTime` on a successfully fetched page.
`Unit`	`setPageGoneSchedule(WebPage page, Instant prevFetchTime, Instant prevModifiedTime, Instant fetchTime)`	This method specifies how to schedule refetching of pages marked as GONE.

Methods inherited from class ai.platon.pulsar.crawl.schedule.AdaptiveFetchSchedule
estimatePrevFetchTime, forceRefetch, initializeSchedule, setPageRetrySchedule, shouldFetch
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - AdaptiveFetchSchedule
```
AdaptiveFetchSchedule(ImmutableConfig conf, MiscMessageWriter messageWriter)
```
- Method Detail
  - getMaxFetchInterval
```
 Duration getMaxFetchInterval()
```
  - getConf
```
 final ImmutableConfig getConf()
```
  - getMessageWriter
```
 final MiscMessageWriter getMessageWriter()
```
  - getParams
```
 Params getParams()
```
  - setFetchSchedule
```
 Unit setFetchSchedule(WebPage page, ModifyInfo m)
```
    Sets the fetchInterval and fetchTime on a successfully fetched page. NOTE: this implementation resets the retry counter - extending classes should call super.setFetchSchedule() to preserve this behavior.
    
    Parameters:
    
    page - The Web page
    
    m - The modification info
  - setPageGoneSchedule
```
 Unit setPageGoneSchedule(WebPage page, Instant prevFetchTime, Instant prevModifiedTime, Instant fetchTime)
```
    This method specifies how to schedule refetching of pages marked as GONE. Default implementation increases fetchInterval by 50% but the value may never exceed maxInterval.