org.transitime.db.hibernate

Class DataDbLogger

java.lang.Object

org.transitime.db.hibernate.DataDbLogger

public class DataDbLogger
extends java.lang.Object

DataDbLogger is for storing to the db a stream of data objects. It is intended for example for storing AVL reports, vehicle matches, arrivals, departures, etc. There can be quite a large volume of this type of data. The database might not always be available. It could be vacuumed, restarted, moved, etc. When this happens don't want the data to be lost and don't want to tie up the core predictor. Therefore a queue is used to log objects. This makes the application far more robust with respect to database issues. The application simply calls add(Object o) to add the object to be stored to the queue. A separate thread is used to read from the queue and write the data to the database. If the queue starts filling up then error messages are e-mailed to users alerting them that there is a problem. E-mail messages are also sent out when the queue level is going down again. A goal with this class was to make the writing to the database is efficient as possible. Therefore the objects are written in batches. This reduces network traffic as well as database load. But this did make handling exceptions more complicated. If there is an exception with a batch then each item is individually written so that don't lose any data. When in playback mode then don't want to store the data because it would interfere with data stored when the application was run in real time. Therefore when running in playback mode set shouldStoreToDb to true when calling getDataDbLogger().

Author:

SkiBu Smith

Method Summary

Modifier and Type	Method and Description
boolean	add(java.lang.Object o) Adds an object to be saved in the database to the queue.
static DataDbLogger	getDataDbLogger(java.lang.String projectId, boolean shouldStoreToDb, boolean shouldPauseToReduceQueue) Factory method.
static void	main(java.lang.String[] args) Just for doing some testing
double	queueLevel() Returns how much capacity of the queue is being used up.
int	queueSize() Returns how many items are in queue to be processed

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getDataDbLogger

public static DataDbLogger getDataDbLogger(java.lang.String projectId,
                                           boolean shouldStoreToDb,
                                           boolean shouldPauseToReduceQueue)

Factory method. Returns the singleton db logger for the specified projectId.

Parameters:

projectId - Id of database to be written to

shouldStoreToDb - Specifies whether data should actually be written to db. If in playback mode and shouldn't write data to db then set to false.

shouldPauseToReduceQueue - Specifies if should pause the thread calling add() if the queue is filling up. Useful for when in batch mode and dumping a whole bunch of data to the db really quickly.

Returns:

The DataDbLogger for the specified projectId

queueLevel

public double queueLevel()

Returns how much capacity of the queue is being used up.

Returns:

a value between 0.0 and 1.0 indicating how much of queue being used

queueSize

public int queueSize()

Returns how many items are in queue to be processed

Returns:

items in queue

add

public boolean add(java.lang.Object o)

Adds an object to be saved in the database to the queue. If queue is getting filled up then an e-mail will be sent out indicating there is a problem. The queue levels at which an e-mail is sent out is specified by levels. If queue has reached capacity then an error message is logged.

Parameters:

o - The object that should be logged to the database

Returns:

True if OK (object added to queue or logging disabled). False if queue was full.

main

public static void main(java.lang.String[] args)

Just for doing some testing

Parameters:

args -