From b49c36f0b0ee45aa7145ac788eb1870897699843 Mon Sep 17 00:00:00 2001
From: sfc-gh-tclinkenbeard <trevor.clinkenbeard@snowflake.com>
Date: Sat, 2 Jul 2022 14:50:09 -0700
Subject: [PATCH] Add StorageQueueInfo::getWriteQueueSizeLimitRatio method

---
 fdbserver/Ratekeeper.actor.cpp           | 19 +++++++++++++++++++
 fdbserver/include/fdbserver/Ratekeeper.h |  3 +++
 2 files changed, 22 insertions(+)

diff --git a/fdbserver/Ratekeeper.actor.cpp b/fdbserver/Ratekeeper.actor.cpp
index 573feb6666..bde7ef6410 100644
--- a/fdbserver/Ratekeeper.actor.cpp
+++ b/fdbserver/Ratekeeper.actor.cpp
@@ -1018,6 +1018,25 @@ void StorageQueueInfo::refreshCommitCost(double elapsed) {
 	totalWriteCosts = 0;
 }
 
+Optional<double> StorageQueueInfo::getWriteQueueSizeLimitRatio(int64_t storageSpringBytes,
+                                                               int64_t storageTargetBytes) const {
+	auto const minFreeSpace =
+	    std::max(SERVER_KNOBS->MIN_AVAILABLE_SPACE,
+	             (int64_t)(SERVER_KNOBS->MIN_AVAILABLE_SPACE_RATIO * smoothTotalSpace.smoothTotal()));
+	auto const storageQueue = getStorageQueueBytes();
+	auto const springBytes = std::max<int64_t>(
+	    1, std::min<int64_t>(storageSpringBytes, (smoothFreeSpace.smoothTotal() - minFreeSpace) * 0.2));
+	auto const targetBytes =
+	    std::max<int64_t>(1, std::min<int64_t>(storageTargetBytes, smoothFreeSpace.smoothTotal() - minFreeSpace));
+	auto const targetRateRatio = std::min((storageQueue - targetBytes + springBytes) / (double)springBytes, 2.0);
+	auto const inputRate = smoothInputBytes.smoothRate();
+	if (targetRateRatio > 0 && inputRate > 0) {
+		return verySmoothDurableBytes.smoothRate() / (inputRate * targetRateRatio);
+	} else {
+		return {};
+	}
+}
+
 TLogQueueInfo::TLogQueueInfo(UID id)
   : valid(false), id(id), smoothDurableBytes(SERVER_KNOBS->SMOOTHING_AMOUNT),
     smoothInputBytes(SERVER_KNOBS->SMOOTHING_AMOUNT), verySmoothDurableBytes(SERVER_KNOBS->SLOW_SMOOTHING_AMOUNT),
diff --git a/fdbserver/include/fdbserver/Ratekeeper.h b/fdbserver/include/fdbserver/Ratekeeper.h
index 948cca851b..a2c79cede9 100644
--- a/fdbserver/include/fdbserver/Ratekeeper.h
+++ b/fdbserver/include/fdbserver/Ratekeeper.h
@@ -73,6 +73,9 @@ public:
 	int64_t getDurabilityLag() const { return smoothLatestVersion.smoothTotal() - smoothDurableVersion.smoothTotal(); }
 	void update(StorageQueuingMetricsReply const&, Smoother& smoothTotalDurableBytes);
 	void addCommitCost(TransactionTagRef tagName, TransactionCommitCostEstimation const& cost);
+
+	// Determine the ratio (limit / current throughput) for throttling based on write queue size
+	Optional<double> getWriteQueueSizeLimitRatio(int64_t storageSpringBytes, int64_t storageTargetBytes) const;
 };
 
 struct TLogQueueInfo {