Array lists with set capacities in SimpleBatcher

[luciopaiva]

Feature Request

This is not exactly a feature request, but a potential enhancement request. While working on #2444, I noticed this array list with a set capacity:

List<RedisCommand<Object, Object, Object>> batch = new ArrayList<>(Math.max(batchSize, 10));

This logic actually appears three times inside SimpleBatcher. My questions are:

• is there any reason for setting the capacity of these array lists? (It's unlikely that it is bringing any noticeable performance enhancements)
• any specific reason for the max(..., 10)?

I'm asking this because in the code I'm working on, I thought about setting @BatchSize() to a huge value like Integer.MAX_VALUE in order to operate solely on manual flushes via flush() calls. The problem is that those lists are being preallocated according to the value in the annotation, so one quickly runs into an OOM if @BatchSize() is too big (that's how I found that code).

My enhancement proposal is to stop setting the capacity on those lists. In case my suggestion is welcome, I would also propose we further improve that code by not even having to allocate new lists inside prepareForceFlush() and prepareDefaultFlush(), but instead relying solely on the one created inside flush() (and thus avoid an unnecessary extra copy as well).

Thoughts? I'd be glad to create a PR for it, but I wanted to check here first if you think it makes sense.

Thanks!

[mp911de]

Preallocation makes some sense to avoid collection resizing. Indeed, the preallocation calculation is wrong, it should rather be Math.min(batchSize, queue.size()).

[mp911de]

That's fixed now.

[luciopaiva]

LGTM. WTG extracting a method there.

Future improvements:

• pass the array list created in flush() to prepareForceFlush() and prepareDefaultFlush() and thus avoid an extra copy
• merge prepareForceFlush() and prepareDefaultFlush() into a single method to simplify the logic

[mp911de]

Feel free to submit a pull request. Happy to merge improvements if they make sense.