From bfccbb2cb5f6eb25981b8693ba8acc5e885c7cce Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Fri, 23 May 2014 11:40:05 -0600
Subject: Avoid trashing page cache on Tx.Copy().

This commit change the database copy to use O_DIRECT so that the Linux page
cache is not trashed during a backup. This is only available on Linux.
---
 bolt.go       | 6 +++++-
 bolt_linux.go | 2 ++
 tx.go         | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/bolt.go b/bolt.go
index c3a1bb5..a3f1eac 100644
--- a/bolt.go
+++ b/bolt.go
@@ -2,7 +2,11 @@
 
 package bolt
 
-import "os"
+import (
+	"os"
+)
+
+var odirect int
 
 func fdatasync(f *os.File) error {
 	return f.Sync()
diff --git a/bolt_linux.go b/bolt_linux.go
index 351b65a..4351db5 100644
--- a/bolt_linux.go
+++ b/bolt_linux.go
@@ -5,6 +5,8 @@ import (
 	"syscall"
 )
 
+var odirect = syscall.O_DIRECT
+
 func fdatasync(f *os.File) error {
 	return syscall.Fdatasync(int(f.Fd()))
 }
diff --git a/tx.go b/tx.go
index 823b06d..8791adf 100644
--- a/tx.go
+++ b/tx.go
@@ -240,7 +240,7 @@ func (tx *Tx) close() {
 // Copy will write exactly tx.Size() bytes into the writer.
 func (tx *Tx) Copy(w io.Writer) error {
 	// Open reader on the database.
-	f, err := os.Open(tx.db.path)
+	f, err := os.OpenFile(tx.db.path, os.O_RDONLY|odirect, 0)
 	if err != nil {
 		_ = tx.Rollback()
 		return err
-- 
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