Factor the saveAllCursors() routine of btree.c into two separate routines,

for a noticable performance improvement.

FossilOrigin-Name: 3eb084390382c108e9b0ff0b29dede58ebb149bc

manifest

@@ -1,5 +1,5 @@
-C Performance\senhancements\sin\sthe\sb-tree\smutex\slogic.
+C Factor\sthe\ssaveAllCursors()\sroutine\sof\sbtree.c\sinto\stwo\sseparate\sroutines,\nfor\sa\snoticable\sperformance\simprovement.
-D 2014-08-22T21:58:10.354
+D 2014-08-22T22:26:07.834
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 5eb79e334a5de69c87740edd56af6527dd219308
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -168,7 +168,7 @@ F src/auth.c 523da7fb4979469955d822ff9298352d6b31de34
 F src/backup.c a31809c65623cc41849b94d368917f8bb66e6a7e
 F src/bitvec.c 19a4ba637bd85f8f63fc8c9bae5ade9fb05ec1cb
 F src/btmutex.c ec9d3f1295dafeb278c3830211cc5584132468f4
-F src/btree.c 4195fed5741b4dbcc9831b623aec487258f3e62d
+F src/btree.c 776885dfef3033af7e8eabbf004481f219870a1d
 F src/btree.h 4245a349bfe09611d7ff887dbc3a80cee8b7955a
 F src/btreeInt.h cf180d86b2e9e418f638d65baa425c4c69c0e0e3
 F src/build.c 058e3aadb1376521ff291735237edf4c10f438fb
@@ -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 6bcf1af6a48dbda5ac6f6b3b02810bdfc4730000
+P 8914530644f938a7a98e25ea1fb0bca1f9d79101
-R 24d5ffe2f1d9679a613707454c70f45a
+R 036983fb95199f1ba06f1397f389a453
 U drh
-Z 6801ae93f83fb9ed7a247305de8bd03a
+Z 9ea20fed62648c22294e9e322338cabb

manifest.uuid

@@ -1 +1 @@
-8914530644f938a7a98e25ea1fb0bca1f9d79101
+3eb084390382c108e9b0ff0b29dede58ebb149bc

src/btree.c

@@ -629,16 +629,42 @@ static int saveCursorPosition(BtCursor *pCur){
   return rc;
 }
 
+/* Forward reference */
+static int SQLITE_NOINLINE saveCursorsOnList(BtCursor*,Pgno,BtCursor*);
+
 /*
 ** Save the positions of all cursors (except pExcept) that are open on
-** the table  with root-page iRoot. Usually, this is called just before cursor
+** the table with root-page iRoot.  "Saving the cursor position" means that
-** pExcept is used to modify the table (BtreeDelete() or BtreeInsert()).
+** the location in the btree is remembered in such a way that it can be
+** moved back to the same spot after the btree has been modified.  This
+** routine is called just before cursor pExcept is used to modify the
+** table, for example in BtreeDelete() or BtreeInsert().
+**
+** Implementation note:  This routine merely checks to see if any cursors
+** need to be saved.  It calls out to saveCursorsOnList() in the (unusual)
+** event that cursors are in need to being saved.
 */
 static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
-  BtCursor *p;
   assert( sqlite3_mutex_held(pBt->mutex) );
   assert( pExcept==0 || pExcept->pBt==pBt );
+  BtCursor *p;
   for(p=pBt->pCursor; p; p=p->pNext){
+    if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ) break;
+  }
+  return p ? saveCursorsOnList(p, iRoot, pExcept) : SQLITE_OK;
+}
+
+/* This helper routine to saveAllCursors does the actual work of saving
+** the cursors if and when a cursor is found that actually requires saving.
+** The common case is that no cursors need to be saved, so this routine is
+** broken out from its caller to avoid unnecessary stack pointer movement.
+*/
+static int SQLITE_NOINLINE saveCursorsOnList(
+  BtCursor *p,           /* The first cursor that needs saving */
+  Pgno iRoot,            /* Only save cursor with this iRoot.  Save all if zero */
+  BtCursor *pExcept      /* Do not save this cursor */
+){
+  do{
     if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ){
       if( p->eState==CURSOR_VALID ){
         int rc = saveCursorPosition(p);
@@ -650,7 +676,8 @@ static int saveAllCursors(BtShared *pBt, Pgno iRoot, BtCursor *pExcept){
         btreeReleaseAllCursorPages(p);
       }
     }
-  }
+    p = p->pNext;
+  }while( p );
   return SQLITE_OK;
 }