From 6fb9013441e346725520c835cd0fbe47a5406c9e Mon Sep 17 00:00:00 2001
From: Aaron Gao <gzh@fb.com>
Date: Thu, 2 Mar 2017 17:11:18 -0800
Subject: [PATCH] sanitize readahead when direct read enabled

Summary:
no readahead:
readseq      :       8.438 micros/op 118510 ops/sec;   13.1 MB/s
sanitize to 10MB:
readseq      :       6.051 micros/op 165248 ops/sec;   18.3 MB/s
Closes https://github.com/facebook/rocksdb/pull/1945

Differential Revision: D4645811

Pulled By: lightmark

fbshipit-source-id: 5d63770
---
 db/db_impl.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/db/db_impl.cc b/db/db_impl.cc
index 8815c7b17..50677200c 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -197,6 +197,10 @@ DBOptions SanitizeOptions(const std::string& dbname, const DBOptions& src) {
     result.db_paths.emplace_back(dbname, std::numeric_limits<uint64_t>::max());
   }
 
+  if (result.use_direct_reads && result.compaction_readahead_size == 0) {
+    result.compaction_readahead_size = 1024 * 1024 * 2;
+  }
+
   if (result.compaction_readahead_size > 0) {
     result.new_table_reader_for_compaction_inputs = true;
   }