Function getStorageBytes

fdbserver/VersionedBTree.actor.cpp:3833–3859

	Future<Void> onClosed() const override { return closedPromise.getFuture(); }

	StorageBytes getStorageBytes() const override {
		int64_t free;
		int64_t total;
		if (memoryOnly) {
			total = pageCache.evictor().sizeLimit;
			free = pageCache.evictor().getSizeUsed();
		} else {
			g_network->getDiskBytes(parentDirectory(filename), free, total);
		}
		int64_t pagerSize = header.pageCount * physicalPageSize;

		// It is not exactly known how many pages on the delayed free list are usable as of right now.  It could be
		// known, if each commit delayed entries that were freeable were shuffled from the delayed free queue to the
		// free queue, but this doesn't seem necessary.

		// Amount of space taken up by all of the items in the free lists
		int64_t reusablePageSpace = (freeList.numEntries + delayedFreeList.numEntries) * physicalPageSize;
		// Amount of space taken up by the free list queues themselves, as if we were to pop and use
		// items on the free lists the space the items are stored in would also become usable
		int64_t reusableQueueSpace = (freeList.numPages + delayedFreeList.numPages) * physicalPageSize;
		int64_t reusable = reusablePageSpace + reusableQueueSpace;

		// Space currently in used by old page versions have have not yet been freed due to the remap cleanup window.
		int64_t temp = remapQueue.numEntries * physicalPageSize;

		return StorageBytes(free, total, pagerSize - reusable, free + reusable, temp);
	}

	int64_t getPageCacheCount() override { return pageCache.getCount(); }
	int64_t getPageCount() override { return header.pageCount; }