Use static inline function for BufferGetPage()

I was initially concerned that the some of the hundreds of
references to BufferGetPage() where the literal
BGP_NO_SNAPSHOT_TEST were passed might not optimize as well as a
macro, leading to some hard-to-find performance regressions in
corner cases.  Inspection of disassembled code has shown identical
code at all inspected locations, and the size difference doesn't
amount to even one byte per such call.  So make it readable.

Per gripes from Álvaro Herrera and Tom Lane

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 29f10e59568792dc8ceea6886298c1dad4f14f67..f402e0dd4b4b5621a0c848c28534a55059e38e7c 100644 (file)
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -4295,7 +4295,7 @@ IssuePendingWritebacks(WritebackContext *context)
  * For best performance, keep the tests that are fastest and/or most likely to
  * exclude a page from old snapshot testing near the front.
  */
-extern Page
+extern void
 TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page)
 {
        Assert(relation != NULL);
@@ -4311,6 +4311,4 @@ TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page)
                ereport(ERROR,
                                (errcode(ERRCODE_SNAPSHOT_TOO_OLD),
                                 errmsg("snapshot too old")));
-
-       return page;
 }

diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index 6fea1bc13dcb93520e3b6c812cf10b378cdd9b72..afd8a847efdb7dbd303fc78e18450fa4323c8923 100644 (file)
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -177,31 +177,6 @@ extern PGDLLIMPORT int32 *LocalRefCount;
        (Size)BLCKSZ \
 )
 
-/*
- * BufferGetPage
- *             Returns the page associated with a buffer.
- *
- * agetest will normally be a literal, so use a macro at the outer level to
- * give the compiler a chance to optimize away the runtime code to check it.
- *
- * TestForOldSnapshot(), if it doesn't throw an error, will return the page
- * argument it is passed, so the same result will go back to this macro's
- * caller for either agetest value; it is a matter of whether to call the
- * function to perform the test.  For call sites where the check is not needed
- * (which is the vast majority of them), the snapshot and relation parameters
- * can, and generally should, be NULL.
- */
-#define BufferGetPage(buffer, snapshot, relation, agetest) \
-( \
-       ( \
-               AssertMacro((agetest) == BGP_NO_SNAPSHOT_TEST || (agetest) == BGP_TEST_FOR_OLD_SNAPSHOT), \
-               ((agetest) == BGP_NO_SNAPSHOT_TEST) \
-       ) ? \
-               ((Page)BufferGetBlock(buffer)) \
-       : \
-               (TestForOldSnapshot(snapshot, relation, (Page)BufferGetBlock(buffer))) \
-)
-
 /*
  * prototypes for functions in bufmgr.c
  */
@@ -268,10 +243,33 @@ extern bool BgBufferSync(struct WritebackContext *wb_context);
 
 extern void AtProcExit_LocalBuffers(void);
 
-extern Page TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page);
+extern void TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page);
 
 /* in freelist.c */
 extern BufferAccessStrategy GetAccessStrategy(BufferAccessStrategyType btype);
 extern void FreeAccessStrategy(BufferAccessStrategy strategy);
 
+
+/* inline functions */
+
+/*
+ * BufferGetPage
+ *             Returns the page associated with a buffer.
+ *
+ * For call sites where the check is not needed (which is the vast majority of
+ * them), the snapshot and relation parameters can, and generally should, be
+ * NULL.
+ */
+static inline Page
+BufferGetPage(Buffer buffer, Snapshot snapshot, Relation relation,
+                         BufferGetPageAgeTest agetest)
+{
+       Page            page = (Page) BufferGetBlock(buffer);
+
+       if (agetest == BGP_TEST_FOR_OLD_SNAPSHOT)
+               TestForOldSnapshot(snapshot, relation, page);
+
+       return page;
+}
+
 #endif