From 7deeb69934ecddba55bd7af9d7b5b87355dd6427 Mon Sep 17 00:00:00 2001
From: Henning Baldersheim <balder@yahoo-inc.com>
Date: Wed, 5 Jan 2022 15:45:34 +0000
Subject: If TLS buffer has more than 8x overhead, shrink it to fit prior to
 posting task for compression. Intention to reduce amount of allocated memory
 in flight in the case there are cpu starvation, or something else causing
 hickups.

---
 searchlib/src/tests/transactionlog/chunks_test.cpp  | 21 +++++++++++++++++++++
 .../src/vespa/searchlib/transactionlog/common.cpp   | 13 +++++++++++++
 .../src/vespa/searchlib/transactionlog/common.h     |  2 ++
 .../src/vespa/searchlib/transactionlog/domain.cpp   |  1 +
 4 files changed, 37 insertions(+)

diff --git a/searchlib/src/tests/transactionlog/chunks_test.cpp b/searchlib/src/tests/transactionlog/chunks_test.cpp
index 8d6620c9f8b..ca03a47634d 100644
--- a/searchlib/src/tests/transactionlog/chunks_test.cpp
+++ b/searchlib/src/tests/transactionlog/chunks_test.cpp
@@ -115,4 +115,25 @@ TEST("test multi element commitchunk") {
     }
     EXPECT_EQUAL(0u, counter);
 }
+
+TEST("shrinkToFit if difference is larger than 8x") {
+    Packet p(16000);
+    p.add(Packet::Entry(1, 3, ConstBufferRef(TEXT, strlen(TEXT))));
+    EXPECT_EQUAL(150u, p.sizeBytes());
+    EXPECT_EQUAL(16384u, p.getHandle().capacity());
+    p.shrinkToFit();
+    EXPECT_EQUAL(150u, p.sizeBytes());
+    EXPECT_EQUAL(150u, p.getHandle().capacity());
+}
+
+TEST("not shrinkToFit if difference is less than 8x") {
+    Packet p(1000);
+    p.add(Packet::Entry(1, 3, ConstBufferRef(TEXT, strlen(TEXT))));
+    EXPECT_EQUAL(150u, p.sizeBytes());
+    EXPECT_EQUAL(1024u, p.getHandle().capacity());
+    p.shrinkToFit();
+    EXPECT_EQUAL(150u, p.sizeBytes());
+    EXPECT_EQUAL(1024u, p.getHandle().capacity());
+}
+
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/searchlib/src/vespa/searchlib/transactionlog/common.cpp b/searchlib/src/vespa/searchlib/transactionlog/common.cpp
index 967f8748174..4130ad0bc06 100644
--- a/searchlib/src/vespa/searchlib/transactionlog/common.cpp
+++ b/searchlib/src/vespa/searchlib/transactionlog/common.cpp
@@ -116,6 +116,14 @@ Packet::add(const Packet::Entry & e)
     _range.to(e.serial());
 }
 
+void
+Packet::shrinkToFit() {
+    if (_buf.size() * 8 < _buf.capacity()) {
+        nbostream::Buffer shrunkToFit(_buf.data(), _buf.data() + _buf.size());
+        _buf.swap(shrunkToFit);
+    }
+}
+
 Writer::CommitResult::CommitResult()
     : _callBacks()
 {}
@@ -151,4 +159,9 @@ CommitChunk::createCommitResult() const {
     return Writer::CommitResult(_callBacks);
 }
 
+void
+CommitChunk::shrinkPayloadToFit() {
+    _data.shrinkToFit();
+}
+
 }
diff --git a/searchlib/src/vespa/searchlib/transactionlog/common.h b/searchlib/src/vespa/searchlib/transactionlog/common.h
index 135681037ef..87150f2cfa9 100644
--- a/searchlib/src/vespa/searchlib/transactionlog/common.h
+++ b/searchlib/src/vespa/searchlib/transactionlog/common.h
@@ -83,6 +83,7 @@ public:
     bool                   empty() const { return _count == 0; }
     size_t             sizeBytes() const { return _buf.size(); }
     void merge(const Packet & packet);
+    void shrinkToFit();
 private:
     size_t                            _count;
     SerialNumRange                    _range;
@@ -143,6 +144,7 @@ public:
     Writer::CommitResult createCommitResult() const;
     void setCommitDoneCallback(Writer::DoneCallback onDone) { _onCommitDone = std::move(onDone); }
     Writer::CommitPayload stealCallbacks() { return std::move(_callBacks); }
+    void shrinkPayloadToFit();
 private:
     Packet                 _data;
     Writer::CommitPayload  _callBacks;
diff --git a/searchlib/src/vespa/searchlib/transactionlog/domain.cpp b/searchlib/src/vespa/searchlib/transactionlog/domain.cpp
index bbde39a42f6..ff35847aa77 100644
--- a/searchlib/src/vespa/searchlib/transactionlog/domain.cpp
+++ b/searchlib/src/vespa/searchlib/transactionlog/domain.cpp
@@ -396,6 +396,7 @@ void
 Domain::commitChunk(std::unique_ptr<CommitChunk> chunk, const UniqueLock & chunkOrderGuard) {
     assert(chunkOrderGuard.mutex() == &_currentChunkMonitor && chunkOrderGuard.owns_lock());
     if (chunk->getPacket().empty()) return;
+    chunk->shrinkPayloadToFit();
     std::promise<SerializedChunk> promise;
     std::future<SerializedChunk> future = promise.get_future();
     _executor.execute(makeLambdaTask([promise=std::move(promise), chunk = std::move(chunk),
-- 
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