Adding excessive read bytes stat

Summary: Adding a stat for excessive read bytes when we read more than the actual size

Reviewed By: haowu14

Differential Revision: D73965289

fbshipit-source-id: cad27ad5692c6cf066216f537582e4db50c0ad82

Author: byahn0996

cachelib/allocator/nvmcache/tests/NvmCacheTests.cpp

@@ -1638,6 +1638,7 @@ TEST_F(NvmCacheTest, NavyStats) {
   EXPECT_TRUE(cs("navy_bc_reinsertions"));
   EXPECT_TRUE(cs("navy_bc_reinsertion_bytes"));
   EXPECT_TRUE(cs("navy_bc_reinsertion_errors"));
+  EXPECT_TRUE(cs("navy_bc_excessive_read_bytes"));
   EXPECT_TRUE(cs("navy_bc_lookup_for_item_destructor_errors"));
   EXPECT_TRUE(cs("navy_bc_reclaim_entry_header_checksum_errors"));
   EXPECT_TRUE(cs("navy_bc_reclaim_value_checksum_errors"));

cachelib/navy/block_cache/BlockCache.cpp

@@ -764,6 +764,7 @@ Status BlockCache::readEntry(const RegionDescriptor& readDesc,
   uint32_t size = serializedSize(desc.keySize, desc.valueSize);
   if (buffer.size() > size) {
     // Read more than actual size. Trim the invalid data in the beginning
+    excessiveReadBytes_.add(buffer.size() - size);
     buffer.trimStart(buffer.size() - size);
   } else if (buffer.size() < size) {
     // Read less than actual size. Read again with proper buffer.
@@ -876,6 +877,8 @@ void BlockCache::getCounters(const CounterVisitor& visitor) const {
           CounterVisitor::CounterType::RATE);
   visitor("navy_bc_reinsertion_errors", reinsertionErrorCount_.get(),
           CounterVisitor::CounterType::RATE);
+  visitor("navy_bc_excessive_read_bytes", excessiveReadBytes_.get(),
+          CounterVisitor::CounterType::RATE);
   visitor("navy_bc_lookup_for_item_destructor_errors",
           lookupForItemDestructorErrorCount_.get(),
           CounterVisitor::CounterType::RATE);

cachelib/navy/block_cache/BlockCache.h

@@ -414,6 +414,7 @@ class BlockCache final : public Engine {
   mutable AtomicCounter cleanupEntryHeaderChecksumErrorCount_;
   mutable AtomicCounter cleanupValueChecksumErrorCount_;
   mutable AtomicCounter lookupForItemDestructorErrorCount_;
+  mutable AtomicCounter excessiveReadBytes_;
 };
 } // namespace navy
 } // namespace cachelib