Avoid XLogFlush for clean buffers in BufferSync.

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 7978924553c44260fe4d3fd644eb4ed6eb909153..7586491ec4849a6eef61e5e7e39859a6ba49e7e6 100644 (file)
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.98 2000/11/30 19:03:25 vadim Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.99 2000/12/22 20:04:43 vadim Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -723,6 +723,7 @@ BufferSync()
    RelFileNode rnode;
    XLogRecPtr  recptr;
    Relation    reln = NULL;
+   bool        dirty = false;
 
    for (i = 0, bufHdr = BufferDescriptors; i < NBuffers; i++, bufHdr++)
    {
@@ -745,6 +746,7 @@ BufferSync()
 
        buffer = BufferDescriptorGetBuffer(bufHdr);
        rnode = bufHdr->tag.rnode;
+       dirty = bufHdr->flags & BM_DIRTY;
 
        SpinRelease(BufMgrLock);
 
@@ -758,6 +760,17 @@ BufferSync()
         */
        LockBuffer(buffer, BUFFER_LOCK_SHARE);
 
+       if (!dirty && !(bufHdr->cntxDirty))
+       {
+           LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+           SpinAcquire(BufMgrLock);
+           UnpinBuffer(bufHdr);
+           SpinRelease(BufMgrLock);
+           if (reln != (Relation) NULL)
+               RelationDecrementReferenceCount(reln);
+           continue;
+       }
+
        /*
         * Force XLOG flush for buffer' LSN
         */
@@ -766,9 +779,8 @@ BufferSync()
 
        /*
         * Now it's safe to write buffer to disk
-        * (if needed at all -:))
+        * (if no one else already)
         */
-
        SpinAcquire(BufMgrLock);
        if (bufHdr->flags & BM_IO_IN_PROGRESS)
            WaitIO(bufHdr, BufMgrLock);
@@ -824,20 +836,19 @@ BufferSync()
             */
            if (!(bufHdr->flags & BM_JUST_DIRTIED))
                bufHdr->flags &= ~BM_DIRTY;
+           UnpinBuffer(bufHdr);
+           SpinRelease(BufMgrLock);
        }
        else
+       {
+           UnpinBuffer(bufHdr);
+           SpinRelease(BufMgrLock);
            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
-
-       UnpinBuffer(bufHdr);
-
-       SpinRelease(BufMgrLock);
+       }
 
        /* drop refcnt obtained by RelationNodeCacheGetRelation */
        if (reln != (Relation) NULL)
-       {
            RelationDecrementReferenceCount(reln);
-           reln = NULL;
-       }
    }
 
 }