org.rhq.enterprise.server.util

Class QueryUtility.PagedDataFetchSettings

java.lang.Object

org.rhq.enterprise.server.util.QueryUtility.PagedDataFetchSettings

Enclosing class:

QueryUtility

public static class QueryUtility.PagedDataFetchSettings
extends Object

A settings object for the QueryUtility.fetchPagedDataAndCount(javax.persistence.Query, javax.persistence.Query, org.rhq.core.domain.util.PageControl, org.rhq.enterprise.server.util.QueryUtility.PagedDataFetchSettings) method.

If a no-arg constructor is used, the instance is initialized with the following values:

• throwOnMaxAttempts - false
• maxAttempts - QueryUtility.PHANTOM_READ_MAX_ATTEMPTS
• minWaitTime - QueryUtility.PHANTOM_READ_MIN_WAIT_TIME
• maxWaitTime - QueryUtility.PHANTOM_READ_MAX_WAIT_TIME

Constructor Summary

Constructors

Constructor and Description
QueryUtility.PagedDataFetchSettings()

Method Summary

Methods

Modifier and Type	Method and Description
float	getLagIncreaseCoefficient() The coefficient of a geometric progression starting from getMinWaitTime() and going to getMaxWaitTime() over getMaxAttempts().
int	getMaxAttempts() Never negative, but might be zero (which has the same semantics as 1).
int	getMaxWaitTime() Positive integer, never 0.
long	getMinimumTotalWaitTime()
int	getMinWaitTime() Positive integer, never 0.
boolean	isThrowOnMaxAttempts()
void	setMaxAttempts(int maxAttempts)
void	setMaxWaitTime(int maxWaitTime)
void	setMinWaitTime(int minWaitTime)
void	setThrowOnMaxAttempts(boolean throwOnMaxAttempts)

Methods inherited from class java.lang.Object

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

Constructor Detail

QueryUtility.PagedDataFetchSettings

public QueryUtility.PagedDataFetchSettings()

Method Detail

getLagIncreaseCoefficient

public float getLagIncreaseCoefficient()

The coefficient of a geometric progression starting from getMinWaitTime() and going to getMaxWaitTime() over getMaxAttempts(). This is how this coefficient is computed and used in QueryUtility.fetchPagedDataAndCount( javax.persistence.Query, javax.persistence.Query, org.rhq.core.domain.util.PageControl, org.rhq.enterprise.server.util.QueryUtility.PagedDataFetchSettings):
fetch(0);
wait(0) = min;
fetch(1);
wait(1) = wait(0) * q;
fetch(2);
wait(2) = wait(1) * q;
...
wait(A-2) = wait(A-3) * q = max;
fetch(A-1);

q = pow(max / min, 1 / (A - 2));
where min is the min wait time, max is max wait time, q is the coefficient and A is the number of attempts.

Computing the pause between the attempts for data fetches this way, we assume that the longer we have inconsistent results, the longer it is probable to last. I.e. all operations are either relatively fast and should clean up in a couple of milliseconds or last quite long.

getMinimumTotalWaitTime

public long getMinimumTotalWaitTime()

Returns:

The minimum time spent when performing maximum number of attempts to prevent a phantom read.

getMaxAttempts

public int getMaxAttempts()

Never negative, but might be zero (which has the same semantics as 1).

setMaxAttempts

public void setMaxAttempts(int maxAttempts)

Throws:

IllegalArgumentException - when a negative value is passed

getMaxWaitTime

public int getMaxWaitTime()

Positive integer, never 0.

setMaxWaitTime

public void setMaxWaitTime(int maxWaitTime)

Throws:

IllegalArgumentException - when a negative number or 0 is passed

getMinWaitTime

public int getMinWaitTime()

Positive integer, never 0.

setMinWaitTime

public void setMinWaitTime(int minWaitTime)

Throws:

IllegalArgumentException - when a negative number or 0 is passed

isThrowOnMaxAttempts

public boolean isThrowOnMaxAttempts()

setThrowOnMaxAttempts

public void setThrowOnMaxAttempts(boolean throwOnMaxAttempts)