Is there a guideline for estimating the amount of memory consumed by a BigDecimal?
Looking for something similar to these guidelines for estimating String memory usage.
If you look at the fields in the source for BigDecimal there is:
BigDecimal:
long intCompact +8 bytes
int precision +4 bytes
int scale +4 bytes
String stringCache +?
BigInteger intVal +?
BigInteger:
int bitCount +4 bytes
int bitLength +4 bytes
int firstNonzeroIntNum +4 bytes
int lowestSetBit +4 bytes
int signum +4 bytes
int[] mag +?
The comment for stringCache says
Used to store the canonical string representation, if computed.
Assuming you don't call .toString(), it will remain zero bytes. Hence BigDecimal is (8+4+4)=16 bytes + BigInteger.
BigInteger itself is 4+4+4+4+4=20 bytes + mag.
20+16 gives total of 36 bytes plus the magnitude, which is always the minimum number of bits necessary to represent the full integer. For a number n it will need log2(n) bits, which can be converted to ints. You should be using about:
36 + Ceiling(log2(n)/8.0) bytes
(note this doesn't include any of the other object descriptor overhead as your example link for strings does, but it should give you a good general idea.)
If you dig into the internals of BigDecimal you'll see that it uses a compact representation if the significand is <= Long.MAX_VALUE. Hence, the memory usage can vary depending on the actual values you're representing.
来源：https://stackoverflow.com/questions/2501176/java-bigdecimal-memory-usage