From 4b6180abef100189278e63a893f8d03c090cd74f Mon Sep 17 00:00:00 2001
From: Bartek Nowotarski <bartek@nowotarski.info>
Date: Wed, 27 May 2020 17:52:54 +0200
Subject: [PATCH] exp/ingest/io: Skip storing live entries seen in the oldest
 bucket (#2618)

This commit updates `SingleLedgerStateReader` to skip updating a temp
ledger key store when processing the oldest bucket. This lowered memory
usage of `SingleLedgerStateReader` from 550MB to 325MB when processing
recent pubnet ledgers.
---
 exp/ingest/io/single_ledger_state_reader.go | 36 +++++++++++++--------
 services/horizon/CHANGELOG.md               |  1 +
 2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/exp/ingest/io/single_ledger_state_reader.go b/exp/ingest/io/single_ledger_state_reader.go
index e9e432cc6c..03623c6d73 100644
--- a/exp/ingest/io/single_ledger_state_reader.go
+++ b/exp/ingest/io/single_ledger_state_reader.go
@@ -160,23 +160,25 @@ func (msr *SingleLedgerStateReader) streamBuckets() {
 		close(msr.readChan)
 	}()
 
-	var buckets []string
+	var buckets []historyarchive.Hash
 	for i := 0; i < len(msr.has.CurrentBuckets); i++ {
 		b := msr.has.CurrentBuckets[i]
-		buckets = append(buckets, b.Curr, b.Snap)
-	}
+		for _, hashString := range []string{b.Curr, b.Snap} {
+			hash, err := historyarchive.DecodeHash(hashString)
+			if err != nil {
+				msr.readChan <- msr.error(errors.Wrap(err, "Error decoding bucket hash"))
+				return
+			}
 
-	for _, hashString := range buckets {
-		hash, err := historyarchive.DecodeHash(hashString)
-		if err != nil {
-			msr.readChan <- msr.error(errors.Wrap(err, "Error decoding bucket hash"))
-			return
-		}
+			if hash.IsZero() {
+				continue
+			}
 
-		if hash.IsZero() {
-			continue
+			buckets = append(buckets, hash)
 		}
+	}
 
+	for i, hash := range buckets {
 		exists, err := msr.bucketExists(hash)
 		if err != nil {
 			msr.readChan <- msr.error(
@@ -192,7 +194,8 @@ func (msr *SingleLedgerStateReader) streamBuckets() {
 			return
 		}
 
-		if shouldContinue := msr.streamBucketContents(hash); !shouldContinue {
+		oldestBucket := i == len(buckets)-1
+		if shouldContinue := msr.streamBucketContents(hash, oldestBucket); !shouldContinue {
 			break
 		}
 	}
@@ -261,7 +264,7 @@ func (msr *SingleLedgerStateReader) newXDRStream(hash historyarchive.Hash) (
 }
 
 // streamBucketContents pushes value onto the read channel, returning false when the channel needs to be closed otherwise true
-func (msr *SingleLedgerStateReader) streamBucketContents(hash historyarchive.Hash) bool {
+func (msr *SingleLedgerStateReader) streamBucketContents(hash historyarchive.Hash, oldestBucket bool) bool {
 	rdr, e := msr.newXDRStream(hash)
 	if e != nil {
 		msr.readChan <- msr.error(
@@ -428,6 +431,13 @@ LoopBucketEntry:
 				// > that the (chronologically) preceding entry with the same ledger
 				// > key was DEADENTRY.
 				if entry.Type == xdr.BucketEntryTypeLiveentry {
+					// We skip adding entries from the last bucket to tempStore because:
+					// 1. Ledger keys are unique within a single bucket.
+					// 2. This is the last bucket we process so there's no need to track
+					//    seen last entries in this bucket.
+					if oldestBucket {
+						continue
+					}
 					err := msr.tempStore.Add(h)
 					if err != nil {
 						msr.readChan <- msr.error(errors.Wrap(err, "Error updating to tempStore"))
diff --git a/services/horizon/CHANGELOG.md b/services/horizon/CHANGELOG.md
index ff7c188bb2..4a1ab05727 100644
--- a/services/horizon/CHANGELOG.md
+++ b/services/horizon/CHANGELOG.md
@@ -8,6 +8,7 @@ file. This project adheres to [Semantic Versioning](http://semver.org/).
 * Drop support for MuxedAccounts strkeys (spec'ed in [SEP23](https://github.com/stellar/stellar-protocol/blob/master/ecosystem/sep-0023.md)).
   SEP23 is still a draft and we don't want to encourage storing strkeys which may not be definite.
 * Replace `SequenceProvider` implementation with one which queries the Horizon DB for sequence numbers instead of the Stellar Core DB.
+* Decreased a memory usage of initial state ingestion stage and state verifier ([#2618](https://github.com/stellar/go/pull/2618)).
 
 ## v1.3.0