Function readMultiPage

fdbserver/VersionedBTree.actor.cpp:3159–3207

	}

	Future<Reference<ArenaPage>> readMultiPage(PagerEventReasons reason,
	                                           unsigned int level,
	                                           VectorRef<PhysicalPageID> pageIDs,
	                                           int priority,
	                                           bool cacheable,
	                                           bool noHit) override {
		// Use cached page if present, without triggering a cache hit.
		// Otherwise, read the page and return it but don't add it to the cache
		debug_printf("DWALPager(%s) op=read %s reason=%s noHit=%d\n",
		             filename.c_str(),
		             toString(pageIDs).c_str(),
		             PagerEventReasonsStrings[(int)reason],
		             noHit);
		auto& eventReasons = g_redwoodMetrics.level(level).metrics.events;
		eventReasons.addEventReason(PagerEvents::CacheLookup, reason);
		if (!cacheable) {
			debug_printf("DWALPager(%s) op=readUncached %s\n", filename.c_str(), toString(pageIDs).c_str());
			PageCacheEntry* pCacheEntry = pageCache.getIfExists(pageIDs.front());
			if (pCacheEntry != nullptr) {
				++g_redwoodMetrics.metric.pagerProbeHit;
				debug_printf("DWALPager(%s) op=readUncachedHit %s\n", filename.c_str(), toString(pageIDs).c_str());
				return pCacheEntry->readFuture;
			}
			++g_redwoodMetrics.metric.pagerProbeMiss;
			debug_printf("DWALPager(%s) op=readUncachedMiss %s\n", filename.c_str(), toString(pageIDs).c_str());
			return forwardError(readPhysicalMultiPage(this, pageIDs, priority), errorPromise);
		}

		PageCacheEntry& cacheEntry = pageCache.get(pageIDs.front(), pageIDs.size() * physicalPageSize, noHit);
		debug_printf("DWALPager(%s) op=read %s cached=%d reading=%d writing=%d noHit=%d\n",
		             filename.c_str(),
		             toString(pageIDs).c_str(),
		             cacheEntry.initialized(),
		             cacheEntry.initialized() && cacheEntry.reading(),
		             cacheEntry.initialized() && cacheEntry.writing(),
		             noHit);
		if (!cacheEntry.initialized()) {
			debug_printf("DWALPager(%s) issuing actual read of %s\n", filename.c_str(), toString(pageIDs).c_str());
			cacheEntry.readFuture = forwardError(readPhysicalMultiPage(this, pageIDs, priority), errorPromise);
			cacheEntry.writeFuture = Void();

			++g_redwoodMetrics.metric.pagerCacheMiss;
			eventReasons.addEventReason(PagerEvents::CacheMiss, reason);
		} else {
			++g_redwoodMetrics.metric.pagerCacheHit;
			eventReasons.addEventReason(PagerEvents::CacheHit, reason);
		}
		return cacheEntry.readFuture;
	}

	PhysicalPageID getPhysicalPageID(LogicalPageID pageID, Version v) {
		auto i = remappedPages.find(pageID);