From: drh <drh@noemail.net>
Date: Fri, 22 Aug 2014 23:33:03 +0000 (+0000)
Subject: Another performance tweak: Split the sqlite3BtreeCursorHasMoved() routine
X-Git-Tag: version-3.8.7~166
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6848dad89477be4146d535e7a2646300c472f429;p=thirdparty%2Fsqlite.git

Another performance tweak: Split the sqlite3BtreeCursorHasMoved() routine
into two with the second routine named sqlite3BtreeCursorRestore().  The first
now only reports whether or not the cursor has moved and the second tries to
restore the cursor.  This allows the sqlite3VdbeCursorMoveto() routine to be
refactored to avoid stack pointer movements, for a noticable performance gain.

FossilOrigin-Name: ce123b5c592556a8cd38b01fcc91ba76231d3098
---

diff --git a/manifest b/manifest
index a0fd1d8b2e..98cd57119e 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Factor\sthe\ssaveAllCursors()\sroutine\sof\sbtree.c\sinto\stwo\sseparate\sroutines,\nfor\sa\snoticable\sperformance\simprovement.
-D 2014-08-22T22:26:07.834
+C Another\sperformance\stweak:\sSplit\sthe\ssqlite3BtreeCursorHasMoved()\sroutine\s\ninto\stwo\swith\sthe\ssecond\sroutine\snamed\ssqlite3BtreeCursorRestore().\s\sThe\sfirst\nnow\sonly\sreports\swhether\sor\snot\sthe\scursor\shas\smoved\sand\sthe\ssecond\stries\sto\nrestore\sthe\scursor.\s\sThis\sallows\sthe\ssqlite3VdbeCursorMoveto()\sroutine\sto\sbe\nrefactored\sto\savoid\sstack\spointer\smovements,\sfor\sa\snoticable\sperformance\sgain.
+D 2014-08-22T23:33:03.189
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 5eb79e334a5de69c87740edd56af6527dd219308
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -168,8 +168,8 @@ F src/auth.c 523da7fb4979469955d822ff9298352d6b31de34
 F src/backup.c a31809c65623cc41849b94d368917f8bb66e6a7e
 F src/bitvec.c 19a4ba637bd85f8f63fc8c9bae5ade9fb05ec1cb
 F src/btmutex.c ec9d3f1295dafeb278c3830211cc5584132468f4
-F src/btree.c 776885dfef3033af7e8eabbf004481f219870a1d
-F src/btree.h 4245a349bfe09611d7ff887dbc3a80cee8b7955a
+F src/btree.c c4b4e1c9524ba7b7dab840e6f8b29e2379a3bdd2
+F src/btree.h a79aa6a71e7f1055f01052b7f821bd1c2dce95c8
 F src/btreeInt.h cf180d86b2e9e418f638d65baa425c4c69c0e0e3
 F src/build.c 058e3aadb1376521ff291735237edf4c10f438fb
 F src/callback.c b97d0695ffcf6a8710ee445ffe56ee387d4d8a6f
@@ -288,7 +288,7 @@ F src/vdbe.c f7f4066e4d6e3858878d76ce9288ea603e12ddf6
 F src/vdbe.h c63fad052c9e7388d551e556e119c0bcf6bebdf8
 F src/vdbeInt.h f5513f2b5ac1e2c5128996c7ea23add256a301df
 F src/vdbeapi.c 49b8d2943d02d276b4efef114578251a3277f47d
-F src/vdbeaux.c f7fdc59e2eefa6fc4ba7324b03ea6f8f66e98d62
+F src/vdbeaux.c dba006f67c9fd1b1d07ee7fb0fb38aa1905161d1
 F src/vdbeblob.c 848238dc73e93e48432991bb5651bf87d865eca4
 F src/vdbemem.c 4a64659ed8e4c3b18a9238e038145ab1bdcd146f
 F src/vdbesort.c f7f5563bf7d4695ca8f3203f3bf9de96d04ed0b3
@@ -1188,7 +1188,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 8914530644f938a7a98e25ea1fb0bca1f9d79101
-R 036983fb95199f1ba06f1397f389a453
+P 3eb084390382c108e9b0ff0b29dede58ebb149bc
+R 356d2e894dc7576ad768e53fab77ee5b
 U drh
-Z 9ea20fed62648c22294e9e322338cabb
+Z 78a9bc2b7c59c5e05ea01f499ba8646b
diff --git a/manifest.uuid b/manifest.uuid
index 334a3ae4c0..af6d676ce0 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-3eb084390382c108e9b0ff0b29dede58ebb149bc
\ No newline at end of file
+ce123b5c592556a8cd38b01fcc91ba76231d3098
\ No newline at end of file
diff --git a/src/btree.c b/src/btree.c
index 6da3715e30..23de31db07 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -762,37 +762,48 @@ static int btreeRestoreCursorPosition(BtCursor *pCur){
          SQLITE_OK)
 
 /*
-** Determine whether or not a cursor has moved from the position it
-** was last placed at.  Cursors can move when the row they are pointing
-** at is deleted out from under them.
-**
-** This routine returns an error code if something goes wrong.  The
-** integer *pHasMoved is set as follows:
-**
-**    0:   The cursor is unchanged
-**    1:   The cursor is still pointing at the same row, but the pointers
-**         returned by sqlite3BtreeKeyFetch() or sqlite3BtreeDataFetch()
-**         might now be invalid because of a balance() or other change to the
-**         b-tree.
-**    2:   The cursor is no longer pointing to the row.  The row might have
-**         been deleted out from under the cursor.
-*/
-int sqlite3BtreeCursorHasMoved(BtCursor *pCur, int *pHasMoved){
+** Determine whether or not a cursor has moved from the position where
+** it was last placed, or has been invalidated for any other reason.
+** Cursors can move when the row they are pointing at is deleted out
+** from under them, for example.  Cursor might also move if a btree
+** is rebalanced.
+**
+** Calling this routine with a NULL cursor pointer returns false.
+**
+** Use the separate sqlite3BtreeCursorRestore() routine to restore a cursor
+** back to where it ought to be if this routine returns true.
+*/
+int sqlite3BtreeCursorHasMoved(BtCursor *pCur){
+  return pCur && pCur->eState!=CURSOR_VALID;
+}
+
+/*
+** This routine restores a cursor back to its original position after it
+** has been moved by some outside activity (such as a btree rebalance or
+** a row having been deleted out from under the cursor).  
+**
+** On success, the *pDifferentRow parameter is false if the cursor is left
+** pointing at exactly the same row.  *pDifferntRow is the row the cursor
+** was pointing to has been deleted, forcing the cursor to point to some
+** nearby row.
+**
+** This routine should only be called for a cursor that just returned
+** TRUE from sqlite3BtreeCursorHasMoved().
+*/
+int sqlite3BtreeCursorRestore(BtCursor *pCur, int *pDifferentRow){
   int rc;
 
-  if( pCur->eState==CURSOR_VALID ){
-    *pHasMoved = 0;
-    return SQLITE_OK;
-  }
+  assert( pCur!=0 );
+  assert( pCur->eState!=CURSOR_VALID );
   rc = restoreCursorPosition(pCur);
   if( rc ){
-    *pHasMoved = 2;
+    *pDifferentRow = 1;
     return rc;
   }
   if( pCur->eState!=CURSOR_VALID || NEVER(pCur->skipNext!=0) ){
-    *pHasMoved = 2;
+    *pDifferentRow = 1;
   }else{
-    *pHasMoved = 1;
+    *pDifferentRow = 0;
   }
   return SQLITE_OK;
 }
diff --git a/src/btree.h b/src/btree.h
index 7118534f93..38abdca1a2 100644
--- a/src/btree.h
+++ b/src/btree.h
@@ -169,7 +169,8 @@ int sqlite3BtreeMovetoUnpacked(
   int bias,
   int *pRes
 );
-int sqlite3BtreeCursorHasMoved(BtCursor*, int*);
+int sqlite3BtreeCursorHasMoved(BtCursor*);
+int sqlite3BtreeCursorRestore(BtCursor*, int*);
 int sqlite3BtreeDelete(BtCursor*);
 int sqlite3BtreeInsert(BtCursor*, const void *pKey, i64 nKey,
                                   const void *pData, int nData,
diff --git a/src/vdbeaux.c b/src/vdbeaux.c
index 58f39a48a8..2037121ddc 100644
--- a/src/vdbeaux.c
+++ b/src/vdbeaux.c
@@ -2713,6 +2713,48 @@ void sqlite3VdbeDelete(Vdbe *p){
   sqlite3DbFree(db, p);
 }
 
+/*
+** The cursor "p" has a pending seek operation that has not yet been
+** carried out.  Seek the cursor now.  If an error occurs, return
+** the appropriate error code.
+*/
+static int SQLITE_NOINLINE handleDeferredMoveto(VdbeCursor *p){
+  int res, rc;
+#ifdef SQLITE_TEST
+  extern int sqlite3_search_count;
+#endif
+  assert( p->deferredMoveto );
+  assert( p->isTable );
+  rc = sqlite3BtreeMovetoUnpacked(p->pCursor, 0, p->movetoTarget, 0, &res);
+  if( rc ) return rc;
+  p->lastRowid = p->movetoTarget;
+  if( res!=0 ) return SQLITE_CORRUPT_BKPT;
+  p->rowidIsValid = 1;
+#ifdef SQLITE_TEST
+  sqlite3_search_count++;
+#endif
+  p->deferredMoveto = 0;
+  p->cacheStatus = CACHE_STALE;
+  return SQLITE_OK;
+}
+
+/*
+** Something has moved cursor "p" out of place.  Maybe the row it was
+** pointed to was deleted out from under it.  Or maybe the btree was
+** rebalanced.  Whatever the cause, try to restore "p" to the place it
+** is suppose to be pointing.  If the row was deleted out from under the
+** cursor, set the cursor to point to a NULL row.
+*/
+static int SQLITE_NOINLINE handleMovedCursor(VdbeCursor *p){
+  int isDifferentRow, rc;
+  assert( p->pCursor!=0 );
+  assert( sqlite3BtreeCursorHasMoved(p->pCursor) );
+  rc = sqlite3BtreeCursorRestore(p->pCursor, &isDifferentRow);
+  p->cacheStatus = CACHE_STALE;
+  if( isDifferentRow ) p->nullRow = 1;
+  return rc;
+}
+
 /*
 ** Make sure the cursor p is ready to read or write the row to which it
 ** was last positioned.  Return an error code if an OOM fault or I/O error
@@ -2728,29 +2770,10 @@ void sqlite3VdbeDelete(Vdbe *p){
 */
 int sqlite3VdbeCursorMoveto(VdbeCursor *p){
   if( p->deferredMoveto ){
-    int res, rc;
-#ifdef SQLITE_TEST
-    extern int sqlite3_search_count;
-#endif
-    assert( p->isTable );
-    rc = sqlite3BtreeMovetoUnpacked(p->pCursor, 0, p->movetoTarget, 0, &res);
-    if( rc ) return rc;
-    p->lastRowid = p->movetoTarget;
-    if( res!=0 ) return SQLITE_CORRUPT_BKPT;
-    p->rowidIsValid = 1;
-#ifdef SQLITE_TEST
-    sqlite3_search_count++;
-#endif
-    p->deferredMoveto = 0;
-    p->cacheStatus = CACHE_STALE;
-  }else if( p->pCursor ){
-    int hasMoved;
-    int rc = sqlite3BtreeCursorHasMoved(p->pCursor, &hasMoved);
-    if( rc ) return rc;
-    if( hasMoved ){
-      p->cacheStatus = CACHE_STALE;
-      if( hasMoved==2 ) p->nullRow = 1;
-    }
+    return handleDeferredMoveto(p);
+  }
+  if( sqlite3BtreeCursorHasMoved(p->pCursor) ){
+    return handleMovedCursor(p);
   }
   return SQLITE_OK;
 }