Simplify the accessPayload() routine so that it always populates the overflow

page cache.  In the one case where populating the page cache can lead to 
problems, simply invalidate the cache as soon as accessPayload() returns.  
This simplification reduces code size and helps accessPayload() to run a 
little faster.  This backs out the eOp==2 mode of accessPayload() added by 
check-in [da59198505].

FossilOrigin-Name: 68e7a8c6765649195ef1ad9407d87d44a307b462

1 files changed, 17 insertions, 26 deletions

diff --git a/src/btree.c b/src/btree.c
index e4a7aa160..2575c774c 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -4424,7 +4424,6 @@ static int copyPayload(
 **
 **   0: The operation is a read. Populate the overflow cache.
 **   1: The operation is a write. Populate the overflow cache.
-**   2: The operation is a read. Do not populate the overflow cache.
 **
 ** A total of "amt" bytes are read or written beginning at "offset".
 ** Data is read to or from the buffer pBuf.
@@ -4432,13 +4431,13 @@ static int copyPayload(
 ** The content being read or written might appear on the main page
 ** or be scattered out on multiple overflow pages.
 **
-** If the current cursor entry uses one or more overflow pages and the
-** eOp argument is not 2, this function may allocate space for and lazily 
-** populates the overflow page-list cache array (BtCursor.aOverflow). 
+** If the current cursor entry uses one or more overflow pages
+** this function may allocate space for and lazily populate
+** the overflow page-list cache array (BtCursor.aOverflow). 
 ** Subsequent calls use this cache to make seeking to the supplied offset 
 ** more efficient.
 **
-** Once an overflow page-list cache has been allocated, it may be
+** Once an overflow page-list cache has been allocated, it must be
 ** invalidated if some other cursor writes to the same table, or if
 ** the cursor is moved to a different row. Additionally, in auto-vacuum
 ** mode, the following events may invalidate an overflow page-list cache.
@@ -4464,10 +4463,10 @@ static int accessPayload(
 #endif
 
   assert( pPage );
+  assert( eOp==0 || eOp==1 );
   assert( pCur->eState==CURSOR_VALID );
   assert( pCur->aiIdx[pCur->iPage]<pPage->nCell );
   assert( cursorHoldsMutex(pCur) );
-  assert( eOp!=2 || offset==0 );    /* Always start from beginning for eOp==2 */
 
   getCellInfo(pCur);
   aPayload = pCur->info.pPayload;
@@ -4489,7 +4488,7 @@ static int accessPayload(
     if( a+offset>pCur->info.nLocal ){
       a = pCur->info.nLocal - offset;
     }
-    rc = copyPayload(&aPayload[offset], pBuf, a, (eOp & 0x01), pPage->pDbPage);
+    rc = copyPayload(&aPayload[offset], pBuf, a, eOp, pPage->pDbPage);
     offset = 0;
     pBuf += a;
     amt -= a;
@@ -4505,14 +4504,13 @@ static int accessPayload(
     nextPage = get4byte(&aPayload[pCur->info.nLocal]);
 
     /* If the BtCursor.aOverflow[] has not been allocated, allocate it now.
-    ** Except, do not allocate aOverflow[] for eOp==2.
     **
     ** The aOverflow[] array is sized at one entry for each overflow page
     ** in the overflow chain. The page number of the first overflow page is
     ** stored in aOverflow[0], etc. A value of 0 in the aOverflow[] array
     ** means "not yet known" (the cache is lazily populated).
     */
-    if( eOp!=2 && (pCur->curFlags & BTCF_ValidOvfl)==0 ){
+    if( (pCur->curFlags & BTCF_ValidOvfl)==0 ){
       int nOvfl = (pCur->info.nPayload-pCur->info.nLocal+ovflSize-1)/ovflSize;
       if( nOvfl>pCur->nOvflAlloc ){
         Pgno *aNew = (Pgno*)sqlite3Realloc(
@@ -4533,9 +4531,7 @@ static int accessPayload(
     ** entry for the first required overflow page is valid, skip
     ** directly to it.
     */
-    if( (pCur->curFlags & BTCF_ValidOvfl)!=0
-     && pCur->aOverflow[offset/ovflSize]
-    ){
+    if( pCur->aOverflow[offset/ovflSize] ){
       iIdx = (offset/ovflSize);
       nextPage = pCur->aOverflow[iIdx];
       offset = (offset%ovflSize);
@@ -4544,12 +4540,10 @@ static int accessPayload(
     assert( rc==SQLITE_OK && amt>0 );
     while( nextPage ){
       /* If required, populate the overflow page-list cache. */
-      if( (pCur->curFlags & BTCF_ValidOvfl)!=0 ){
-        assert( pCur->aOverflow[iIdx]==0
-                || pCur->aOverflow[iIdx]==nextPage
-                || CORRUPT_DB );
-        pCur->aOverflow[iIdx] = nextPage;
-      }
+      assert( pCur->aOverflow[iIdx]==0
+              || pCur->aOverflow[iIdx]==nextPage
+              || CORRUPT_DB );
+      pCur->aOverflow[iIdx] = nextPage;
 
       if( offset>=ovflSize ){
         /* The only reason to read this page is to obtain the page
@@ -4557,11 +4551,7 @@ static int accessPayload(
         ** data is not required. So first try to lookup the overflow
         ** page-list cache, if any, then fall back to the getOverflowPage()
         ** function.
-        **
-        ** Note that the aOverflow[] array must be allocated because eOp!=2
-        ** here.  If eOp==2, then offset==0 and this branch is never taken.
         */
-        assert( eOp!=2 );
         assert( pCur->curFlags & BTCF_ValidOvfl );
         assert( pCur->pBtree->db==pBt->db );
         if( pCur->aOverflow[iIdx+1] ){
@@ -4596,7 +4586,7 @@ static int accessPayload(
         ** output buffer, bypassing the page-cache altogether. This speeds
         ** up loading large records that span many overflow pages.
         */
-        if( (eOp&0x01)==0                                      /* (1) */
+        if( eOp==0                                             /* (1) */
          && offset==0                                          /* (2) */
          && pBt->inTransaction==TRANS_READ                     /* (3) */
          && (fd = sqlite3PagerFile(pBt->pPager))->pMethods     /* (4) */
@@ -4616,12 +4606,12 @@ static int accessPayload(
         {
           DbPage *pDbPage;
           rc = sqlite3PagerGet(pBt->pPager, nextPage, &pDbPage,
-              ((eOp&0x01)==0 ? PAGER_GET_READONLY : 0)
+              (eOp==0 ? PAGER_GET_READONLY : 0)
           );
           if( rc==SQLITE_OK ){
             aPayload = sqlite3PagerGetData(pDbPage);
             nextPage = get4byte(aPayload);
-            rc = copyPayload(&aPayload[offset+4], pBuf, a, (eOp&0x01), pDbPage);
+            rc = copyPayload(&aPayload[offset+4], pBuf, a, eOp, pDbPage);
             sqlite3PagerUnref(pDbPage);
             offset = 0;
           }
@@ -5253,7 +5243,8 @@ int sqlite3BtreeMovetoUnpacked(
             goto moveto_finish;
           }
           pCur->aiIdx[pCur->iPage] = (u16)idx;
-          rc = accessPayload(pCur, 0, nCell, (unsigned char*)pCellKey, 2);
+          rc = accessPayload(pCur, 0, nCell, (unsigned char*)pCellKey, 0);
+          pCur->curFlags &= ~BTCF_ValidOvfl;
           if( rc ){
             sqlite3_free(pCellKey);
             goto moveto_finish;