fix item_count of ScrambledZipfianGenerator

[junhanLee95]

Hello,
The generator_ of ScrambledZipfianGenerator is incorrectly initialized.
If $min and $max is declared in the constructor, the $item_count should be $max - $min + 1, not 10000000000LL.
You can check the original YCSB source code in the following link below.
(https://github.com/brianfrankcooper/YCSB/blob/master/core/src/main/java/site/ycsb/generator/ScrambledZipfianGenerator.java#L87)

[ls4154]

Hi,
Original YCSB also seems to initialize the ZipfianGenerator with the constant ITEM_COUNT (= 10000000000L).
The variable itemcount (equivalent to num_items_ in YCSB-cpp) is only used for modular operation in nextValue.

please let me know if I'm missing something!

[junhanLee95]

Thank you for the reply.

As you shown in the source code L87 what I attached, $itemcount is reset to $max - $min + 1, which is passed to ZipfianGenerator().

Moreover, you can check this in YCSB-C source code.
The zipfian generator within scrambled zipfian generator also passed the input arguments as generator_(min, max, zipfian_const), in L26, instead of 10000000000L.

Please check the file below.
(https://github.com/basicthinker/YCSB-C/blob/6475c7a5c3c7b229224ce5ca3332a58c994b8a09/core/scrambled_zipfian_generator.h#L26)

[ls4154]

As you shown in the source code L87 what I attached, $itemcount is reset to $max - $min + 1, which is passed to ZipfianGenerator().

In YCSB, the ZipfianGenerator is initialized with ITEM_COUNT, which is different from the itemcount.
ITEM_COUNT is a static constant, while itemcount is a member variable.

// ScrambledZipfianGenerator.java Line 35
public static final long ITEM_COUNT = 10000000000L;

// ScrambledZipfianGenerator.java Line 38
private final long min, max, itemcount;

// ScrambledZipfianGenerator.java Line 87-92
itemcount = this.max - this.min + 1;
if (zipfianconstant == USED_ZIPFIAN_CONSTANT) {
  gen = new ZipfianGenerator(0, ITEM_COUNT, zipfianconstant, ZETAN);
} else {
  gen = new ZipfianGenerator(0, ITEM_COUNT, zipfianconstant);
}

Moreover, you can check this in YCSB-C source code.
The zipfian generator within scrambled zipfian generator also passed the input arguments as generator_(min, max, zipfian_const), in L26, instead of 10000000000L.

While I don't remember the details, I think I modified that part to make the ScrambledZipfianGenerator works the same as the one in the original YCSB code. Maybe, passing the itemcount to ZipfianGenerator could be right, there was a discussion about this issue. However, the goal of YCSB-cpp is to implement the YCSB as it is in C++, so it would be better to follow original code behavior.

[ls4154]

Closed due to inactivity.