Add error log in BlockCache::readEntry when there is value checksum mismatch

Summary: Add log to further investigate the recent nvm disable issue in memcache T138539066.

Reviewed By: lenar-f, jaesoo-fb

Differential Revision: D41658294

fbshipit-source-id: cc4116b037a0a7f9118644f69a7788d8204e6c48

Author: Jiayue Bao

cachelib/navy/block_cache/BlockCache.cpp

@@ -668,6 +668,10 @@ Status BlockCache::readEntry(const RegionDescriptor& readDesc,
   value = std::move(buffer);
   value.shrink(desc.valueSize);
   if (checksumData_ && desc.cs != checksum(value.view())) {
+    XLOG_N_PER_MS(ERR, 10, 10'000) << folly::sformat(
+        "Item value checksum mismatch when looking up key {}. "
+        "Expected:{}, Actual: {}.",
+        key, desc.cs, checksum(value.view()));
     value.reset();
     lookupValueChecksumErrorCount_.inc();
     return Status::DeviceError;