Rearrange fields of the BtCursor object so that it is smaller and requires less

initialization, for a small performance improvement.

FossilOrigin-Name: 0ddf5292cc0411ec6fcb7399ecf2904c899e0488404d3f65490fbe1db15efdf4

manifest

@@ -1,5 +1,5 @@
-C Add\sthe\snormalize.c\sextension.
-D 2018-01-24T15:07:37.708
+C Rearrange\sfields\sof\sthe\sBtCursor\sobject\sso\sthat\sit\sis\ssmaller\sand\srequires\sless\ninitialization,\sfor\sa\ssmall\sperformance\simprovement.
+D 2018-01-24T16:04:21.587
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 7a3f714b4fcf793108042b7b0a5c720b0b310ec84314d61ba7f3f49f27e550ea
@@ -429,9 +429,9 @@ F src/auth.c 6277d63837357549fe14e723490d6dc1a38768d71c795c5eb5c0f8a99f918f73
 F src/backup.c faf17e60b43233c214aae6a8179d24503a61e83b
 F src/bitvec.c 17ea48eff8ba979f1f5b04cc484c7bb2be632f33
 F src/btmutex.c 0e9ce2d56159b89b9bc8e197e023ee11e39ff8ca
-F src/btree.c 1beceb1c5f9563271241fd0c294484668e4ad28cf6aa970eab70e50ff6f75e25
+F src/btree.c d711228cac336fb35fff21f3f4a0efe2ad58aa9a800dd02929cdf184be1e78a3
 F src/btree.h 0866c0a08255142ea0e754aabd211c843cab32045c978a592a43152405ed0c84
-F src/btreeInt.h 6e70d15435b60a29386ae9864875618ca225c31bf815038bbd8f510a66bb9cb1
+F src/btreeInt.h 620ab4c7235f43572cf3ac2ac8723cbdf68073be4d29da24897c7b77dda5fd96
 F src/build.c 9f9647454f236cab097f266ae970f899b53c71cadab6756c47e2b2e81392c2a1
 F src/callback.c fe677cb5f5abb02f7a772a62a98c2f516426081df68856e8f2d5f950929b966a
 F src/complete.c a3634ab1e687055cd002e11b8f43eb75c17da23e
@@ -1702,8 +1702,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P e0f192ea6dda4fa0b243d58c8ce41932519141bcae0689a90318b4f866f54edd 658f42257d56a3562dfa8e55023c6e497f55c565cd751d942de3a9e0cb2fa708
-R 01bd832eb21dc9b5a19a52a2b0f11c48
-T +closed 658f42257d56a3562dfa8e55023c6e497f55c565cd751d942de3a9e0cb2fa708
+P 16ebe558d2f0982f630c39b6c1b00d14d27011d454cced213f17c26491a2c06e
+R fc9e02eb09b9540ef2f7fa9944ac0566
 U drh
-Z 043a35201b0c771ecddffe95c53bb65f
+Z c7e32730b85a19ed6c94c7a445674e7d

manifest.uuid

@@ -1 +1 @@
-16ebe558d2f0982f630c39b6c1b00d14d27011d454cced213f17c26491a2c06e
+0ddf5292cc0411ec6fcb7399ecf2904c899e0488404d3f65490fbe1db15efdf4

src/btree.c

@@ -4345,7 +4345,7 @@ int sqlite3BtreeCursorSize(void){
 ** of run-time by skipping the initialization of those elements.
 */
 void sqlite3BtreeCursorZero(BtCursor *p){
-  memset(p, 0, offsetof(BtCursor, iPage));
+  memset(p, 0, offsetof(BtCursor, BTCURSOR_FIRST_UNINIT));
 }
 
 /*
@@ -4668,14 +4668,15 @@ static int accessPayload(
     */
     if( (pCur->curFlags & BTCF_ValidOvfl)==0 ){
       int nOvfl = (pCur->info.nPayload-pCur->info.nLocal+ovflSize-1)/ovflSize;
-      if( nOvfl>pCur->nOvflAlloc ){
+      if( pCur->aOverflow==0
+       || nOvfl*sizeof(Pgno) > sqlite3MallocSize(pCur->aOverflow)
+      ){
         Pgno *aNew = (Pgno*)sqlite3Realloc(
             pCur->aOverflow, nOvfl*2*sizeof(Pgno)
         );
         if( aNew==0 ){
           return SQLITE_NOMEM_BKPT;
         }else{
-          pCur->nOvflAlloc = nOvfl*2;
           pCur->aOverflow = aNew;
         }
       }

src/btreeInt.h

@@ -503,20 +503,20 @@ struct BtCursor {
   u8 curFlags;              /* zero or more BTCF_* flags defined below */
   u8 curPagerFlags;         /* Flags to send to sqlite3PagerGet() */
   u8 hints;                 /* As configured by CursorSetHints() */
-  int nOvflAlloc;           /* Allocated size of aOverflow[] array */
-  Btree *pBtree;            /* The Btree to which this cursor belongs */
-  BtShared *pBt;            /* The BtShared this cursor points to */
-  BtCursor *pNext;          /* Forms a linked list of all cursors */
-  Pgno *aOverflow;          /* Cache of overflow page locations */
-  CellInfo info;            /* A parse of the cell we are pointing at */
-  i64 nKey;                 /* Size of pKey, or last integer key */
-  void *pKey;               /* Saved key that was cursor last known position */
-  Pgno pgnoRoot;            /* The root page of this tree */
   int skipNext;    /* Prev() is noop if negative. Next() is noop if positive.
                    ** Error code if eState==CURSOR_FAULT */
+  Btree *pBtree;            /* The Btree to which this cursor belongs */
+  Pgno *aOverflow;          /* Cache of overflow page locations */
+  void *pKey;               /* Saved key that was cursor last known position */
   /* All fields above are zeroed when the cursor is allocated.  See
   ** sqlite3BtreeCursorZero().  Fields that follow must be manually
   ** initialized. */
+#define BTCURSOR_FIRST_UNINIT pBt   /* Name of first uninitialized field */
+  BtShared *pBt;            /* The BtShared this cursor points to */
+  BtCursor *pNext;          /* Forms a linked list of all cursors */
+  CellInfo info;            /* A parse of the cell we are pointing at */
+  i64 nKey;                 /* Size of pKey, or last integer key */
+  Pgno pgnoRoot;            /* The root page of this tree */
   i8 iPage;                 /* Index of current page in apPage */
   u8 curIntKey;             /* Value of apPage[0]->intKey */
   u16 ix;                   /* Current index for apPage[iPage] */