Class DiskQueue

fdbserver/DiskQueue.actor.cpp:881–1392

};

class DiskQueue final : public IDiskQueue, public Tracked<DiskQueue> {
public:
	// FIXME: Is setting lastCommittedSeq to -1 instead of 0 necessary?
	DiskQueue(std::string basename,
	          std::string fileExtension,
	          UID dbgid,
	          DiskQueueVersion diskQueueVersion,
	          int64_t fileSizeWarningLimit)
	  : rawQueue(new RawDiskQueue_TwoFiles(basename, fileExtension, dbgid, fileSizeWarningLimit)), dbgid(dbgid),
	    diskQueueVersion(diskQueueVersion), anyPopped(false), warnAlwaysForMemory(true), nextPageSeq(0), poppedSeq(0),
	    lastPoppedSeq(0), lastCommittedSeq(-1), pushed_page_buffer(nullptr), recovered(false), initialized(false),
	    nextReadLocation(-1), readBufPage(nullptr), readBufPos(0) {}

	location push(StringRef contents) override {
		ASSERT(recovered);
		uint8_t const* begin = contents.begin();
		uint8_t const* end = contents.end();
		CODE_PROBE(contents.size() && pushedPageCount(), "More than one push between commits");

		bool pushAtEndOfPage = contents.size() >= 4 && pushedPageCount() && backPage().remainingCapacity() < 4;
		CODE_PROBE(pushAtEndOfPage, "Push right at the end of a page, possibly splitting size");
		while (begin != end) {
			if (!pushedPageCount() || !backPage().remainingCapacity())
				addEmptyPage();

			auto& p = backPage();
			int s = std::min<int>(p.remainingCapacity(), end - begin);
			memcpy(p.payload + p.payloadSize, begin, s);
			p.payloadSize += s;
			begin += s;
		}
		return endLocation();
	}

	void pop(location upTo) override {
		ASSERT(!upTo.hi);
		ASSERT(!recovered || upTo.lo <= endLocation());

		// SS can pop pages that have not been sync.ed to disk because of concurrency:
		//   SS can read (i.e., pop) data at the same time or before tLog syncs the page to disk.
		//   This is rare in real situation but common in simulation.
		// The following ASSERT is NOT part of the intended contract of IDiskQueue, but alerts the user to a known bug
		// where popping
		//  into uncommitted pages can cause a durability failure.
		// FIXME: Remove this ASSERT when popping into uncommitted pages is fixed
		if (upTo.lo > lastCommittedSeq) {
			TraceEvent(SevError, "DQPopUncommittedData", dbgid)
			    .detail("UpTo", upTo)
			    .detail("LastCommittedSeq", lastCommittedSeq)
			    .detail("File0Name", rawQueue->files[0].dbgFilename);
		}
		if (upTo.lo > poppedSeq) {
			poppedSeq = upTo.lo;
			anyPopped = true;
		}
	}

	Future<Standalone<StringRef>> read(location from, location to, CheckHashes ch) override {