Fix VerifyChecksum readahead with mmap mode (#5945)

Summary:
A recent change introduced readahead inside VerifyChecksum(). However it is not compatible with mmap mode and generated wrong checksum verification failure. Fix it by not enabling readahead in mmap
 mode.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5945

Test Plan: Add a unit test that used to fail.

Differential Revision: D18021443

fbshipit-source-id: 6f2eb600f81b26edb02222563a4006869d576bff

diff --git a/db/corruption_test.cc b/db/corruption_test.cc
index 3fd85953db311ff22a1e553eed0da42ee7145750..4add9b26a2f0c0699cc9059a8d41258fbc4eb9ed 100644 (file)
--- a/db/corruption_test.cc
+++ b/db/corruption_test.cc
@@ -369,6 +369,13 @@ TEST_F(CorruptionTest, VerifyChecksumReadahead) {
   ASSERT_GE(senv.random_read_counter_.Read(), 213);
   ASSERT_LE(senv.random_read_counter_.Read(), 447);
 
+  // Test readahead shouldn't break mmap mode (where it should be
+  // disabled).
+  options.allow_mmap_reads = true;
+  Reopen(&options);
+  dbi = static_cast<DBImpl*>(db_);
+  ASSERT_OK(dbi->VerifyChecksum(ro));
+
   CloseDb();
 }
 

diff --git a/table/block_based/block_based_table_reader.cc b/table/block_based/block_based_table_reader.cc
index be06c74da1cc628dfc085fccaf2517a9ded641e9..b0971cf72508e6d44a1781deaa18705c42c9c5b8 100644 (file)
--- a/table/block_based/block_based_table_reader.cc
+++ b/table/block_based/block_based_table_reader.cc
@@ -3746,8 +3746,12 @@ Status BlockBasedTable::VerifyChecksumInBlocks(
   size_t readahead_size = (read_options.readahead_size != 0)
                               ? read_options.readahead_size
                               : kMaxAutoReadaheadSize;
-  FilePrefetchBuffer prefetch_buffer(rep_->file.get(), readahead_size,
-                                     readahead_size);
+  // FilePrefetchBuffer doesn't work in mmap mode and readahead is not
+  // needed there.
+  FilePrefetchBuffer prefetch_buffer(
+      rep_->file.get(), readahead_size /* readadhead_size */,
+      readahead_size /* max_readahead_size */,
+      !rep_->ioptions.allow_mmap_reads /* enable */);
 
   for (index_iter->SeekToFirst(); index_iter->Valid(); index_iter->Next()) {
     s = index_iter->status();