CaffeineCache calculates the "weight" of individual entries at insertion time, using weigh function:
private int weigh(Object oKey, Object oValue)
{
int cUnits = m_unitCalculator.calculateUnits(oKey, oValue);
if (cUnits < 0)
{
throw new IllegalStateException(String.format(
"Negative unit (%s) for %s=%s", cUnits, oKey, oValue));
}
return (cUnits / m_nUnitFactor);
}
This is problematic, because the method above returns 0 if a unit factor is larger than the number of units for a give entry, which is often the case when unit factor is used (typical values for unit factor are 2^10 and 2^20, in order to track and limit cache size in KBs or MBs). Even if the factor is smaller than the entry size, the loss of precision due to integer arithmetic at the single entry level is significant.
To Reproduce
Configure unit factor that is larger than the average entry size
Configure BINARY unit calculator
Add some entries to the cache
Observe that the getUnits method returns zero, even though there are entries in the cache
Expected behaviorgetUnits methods should return the actual number of bytes consumed by all entries, divided by the unit factor.
In other words, unit factor should only be applied during final calculation for the backing map as a whole, not at the individual entry level.
Environment (please complete the following information):
rlubke
commented
2 years ago
Describe the bug
CaffeineCachecalculates the "weight" of individual entries at insertion time, usingweighfunction:This is problematic, because the method above returns 0 if a unit factor is larger than the number of units for a give entry, which is often the case when unit factor is used (typical values for unit factor are 2^10 and 2^20, in order to track and limit cache size in KBs or MBs). Even if the factor is smaller than the entry size, the loss of precision due to integer arithmetic at the single entry level is significant.
To Reproduce
getUnitsmethod returns zero, even though there are entries in the cacheExpected behavior
getUnitsmethods should return the actual number of bytes consumed by all entries, divided by the unit factor.In other words, unit factor should only be applied during final calculation for the backing map as a whole, not at the individual entry level.
Environment (please complete the following information):