Performance enhancement: avoid calling reparentChildPages() from balance_nonroot(). (CVS 5743)

FossilOrigin-Name: 28fd0a50ca8529892f5b1ababd38d494889eed6d

manifest

@@ -1,5 +1,5 @@
-C On\swindows,\savoid\srunning\sthose\stests\sin\sexclusive.test\sthat\srequire\sthe\sjournal\sfile\sto\sbe\sexternally\saccessed\swhile\sSQLite\sis\sholding\sit\sopen.\sThis\sdoesn't\swork\son\swindows.\s(CVS\s5742)
-D 2008-09-24T14:03:43
+C Performance\senhancement:\savoid\scalling\sreparentChildPages()\sfrom\sbalance_nonroot().\s(CVS\s5743)
+D 2008-09-26T17:31:55
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in e4ab842f9a64ef61d57093539a8aab76b12810db
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -99,7 +99,7 @@ F src/attach.c db3f4a60538733c1e4dcb9d0217a6e0d6ccd615b
 F src/auth.c c8b2ab5c8bad4bd90ed7c294694f48269162c627
 F src/bitvec.c 95c86bd18d8fedf0533f5af196192546e10a7e7d
 F src/btmutex.c 709cad2cdca0afd013f0f612363810e53f59ec53
-F src/btree.c 4d642d23fc4507089f702eb24b506be2ce7e0efd
+F src/btree.c 850d7ede7fe58f8bfad78131278ceff83817abf5
 F src/btree.h 6371c5e599fab391a150c96afbc10062b276d107
 F src/btreeInt.h e36f77e6621d671beb19ae581af1eba116cdfdc4
 F src/build.c 160c71acca8f643f436ed6c1ee2f684c88df4dfe
@@ -637,7 +637,7 @@ F tool/speedtest16.c c8a9c793df96db7e4933f0852abb7a03d48f2e81
 F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 1dbced29de5f59ba2ebf877edcadf171540374d1
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
-P 0acca5842f83943228d4225b60dc7e8a42bae577
-R 9eb08ed19a8499580c1afb4ad41aa2b7
+P 5debf12fa46520946ac5da44c03448fffbc9940c
+R ad8baa95733fbb9a312a15654e608ce1
 U danielk1977
-Z 7daec82c5a8b96a531bdb9c3bccd5b3b
+Z 410e2e4a76b6dc0451fd1f6a24aebc75

manifest.uuid

@@ -1 +1 @@
-5debf12fa46520946ac5da44c03448fffbc9940c
+28fd0a50ca8529892f5b1ababd38d494889eed6d

src/btree.c

@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btree.c,v 1.516 2008/09/19 16:39:38 danielk1977 Exp $
+** $Id: btree.c,v 1.517 2008/09/26 17:31:55 danielk1977 Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** See the header comment on "btreeInt.h" for additional information.
@@ -5586,14 +5586,46 @@ static int balance_nonroot(MemPage *pPage){
   }
 
   /*
-  ** Reparent children of all cells.
+  ** At this point we used to call reparentChildPages() to make sure that
+  ** the MemPage.pParent and MemPage.idxParent variables are correct for
+  ** all children of the pages modified by this balance operation. Even
+  ** if this is an auto-vacuum database there is no need to update the
+  ** pointer-map entries for child pages - that has already been done
+  ** by the block above.
+  **
+  ** However, this is no longer necessary because the MemPage.pParent and
+  ** MemPage.idxParent variables are only assumed to be valid when there
+  ** are one or more references to the page (when isInit==PAGE_ISINIT_FULL). 
+  ** At this point we can account for all references to the pages
+  ** manipulated by this function and deduce that it is not necessary to
+  ** update these two variables because:
+  **
+  **   a) it must have been called, directly or indirectly, from BtreeInsert()
+  **      or BtreeDelete(). Both these functions call saveAllCursors(), so
+  **      we can be sure that there exactly one write-cursor (and no
+  **      read-cursors) open on the b-tree being manipulated. No other
+  **      cursor may be holding references to any pages in the b-tree.
+  **
+  **   b) After this function returns, the one open write-cursor will be
+  **      moved to point at the root of the table using moveToRoot(). The
+  **      code that does this (see BtreeInsert() and BtreeDelete()) ensures
+  **      that the MemPage.pParent variables are not used to find the root
+  **      page of the b-tree, it is located using BtCursor.pgnoRoot.
+  **
+  **   c) the other page references are those held by this function, on
+  **      the pages in apNew[] and apOld[]. They are about to be released.
+  **
+  ** Therefore, no need to call reparentChildPages(). This can be a
+  ** significant performance boost.
   */
+#if 0
   for(i=0; i<nNew; i++){
     rc = reparentChildPages(apNew[i], 0);
     if( rc!=SQLITE_OK ) goto balance_cleanup;
   }
   rc = reparentChildPages(pParent, 0);
   if( rc!=SQLITE_OK ) goto balance_cleanup;
+#endif
 
   /*
   ** Balance the parent page.  Note that the current page (pPage) might
@@ -5973,6 +6005,13 @@ int sqlite3BtreeInsert(
   if( rc!=SQLITE_OK ) goto end_insert;
   rc = balance(pPage, 1);
   if( rc==SQLITE_OK ){
+    /* balance() may have messed up the chain of MemPage.pParent pointers.
+    ** To prevent moveToRoot() from trying to use them to locate the root
+    ** page of this table, release the reference to the current page before
+    ** calling it.
+    */
+    releasePage(pCur->pPage);
+    pCur->pPage = 0;
     moveToRoot(pCur);
   }
 end_insert:
@@ -6089,6 +6128,13 @@ int sqlite3BtreeDelete(BtCursor *pCur){
     rc = balance(pPage, 0);
   }
   if( rc==SQLITE_OK ){
+    /* balance() may have messed up the chain of MemPage.pParent pointers.
+    ** To prevent moveToRoot() from trying to use them to locate the root
+    ** page of this table, release the reference to the current page before
+    ** calling it.
+    */
+    releasePage(pCur->pPage);
+    pCur->pPage = 0;
     moveToRoot(pCur);
   }
   return rc;