Avoid writing the sqlite_sequence table when it has not actually changed.

FossilOrigin-Name: 3e3849a9d1a06673e6c713a42194f5da339fbf6533fa418c38f63d09bc045867

manifest

@@ -1,5 +1,5 @@
-C Fix\sa\sproblem\sin\stest\sscript\sthread001.test\scausing\sa\sspurious\s"-1\sfiles\swere\nleft\sopen"\serror\swhen\srun\sseparately.
-D 2018-03-16T07:48:43.361
+C Avoid\swriting\sthe\ssqlite_sequence\stable\swhen\sit\shas\snot\sactually\schanged.
+D 2018-03-16T18:46:30.654
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 7016fc56c6b9bfe5daac4f34be8be38d8c0b5fab79ccbfb764d3b23bf1c6fff3
@@ -450,7 +450,7 @@ F src/hash.c a12580e143f10301ed5166ea4964ae2853d3905a511d4e0c44497245c7ce1f7a
 F src/hash.h ab34c5c54a9e9de2e790b24349ba5aab3dbb4fd4
 F src/hwtime.h 747c1bbe9df21a92e9c50f3bbec1de841dc5e5da
 F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
-F src/insert.c 14686083cedc198540b15a79586cdd4be2acf6d5fa97627e355f817ab07e9fee
+F src/insert.c b9ff71cc2913d1d57698a1e22bf853261a9a642baf62bdf40ddeb3809adb85b5
 F src/legacy.c 134ab3e3fae00a0f67a5187981d6935b24b337bcf0f4b3e5c9fa5763da95bf4e
 F src/loadext.c f6e4e416a736369f9e80eba609f0acda97148a8b0453784d670c78d3eed2f302
 F src/main.c c1e97e4c6fffff1fb1a6f1c48807386819af78657b4ae4acfd6d6d17353b8277
@@ -1712,7 +1712,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P f1784aff4e6ff1c84d3fa0069034290154220fd2fa85c7df342c717ad54f4b91
-R 6365d4cb8120ab9ac72d818a9b1d70a0
-U dan
-Z b450edce4db91ca834c891cd7015f37d
+P 1774f1c3baf0bc3d83a53c52702696ff21814fa1de07cc38fd098832e6757b09
+R d0bd8d3f666390fa87cc4ce598933023
+T *branch * autoinc-enhancement
+T *sym-autoinc-enhancement *
+T -sym-trunk *
+U drh
+Z 5d34c90db248f39c50f1168b98361d2f

manifest.uuid

@@ -1 +1 @@
-1774f1c3baf0bc3d83a53c52702696ff21814fa1de07cc38fd098832e6757b09
+3e3849a9d1a06673e6c713a42194f5da339fbf6533fa418c38f63d09bc045867

src/insert.c

@@ -210,11 +210,12 @@ static int readsTable(Parse *p, int iDb, Table *pTab){
 ** first use of table pTab.  On 2nd and subsequent uses, the original
 ** AutoincInfo structure is used.
 **
-** Three memory locations are allocated:
+** Four consecutive registers are allocated:
 **
-**   (1)  Register to hold the name of the pTab table.
-**   (2)  Register to hold the maximum ROWID of pTab.
-**   (3)  Register to hold the rowid in sqlite_sequence of pTab
+**   (1)  The name of the pTab table.
+**   (2)  The maximum ROWID of pTab.
+**   (3)  The rowid in sqlite_sequence of pTab
+**   (4)  The original value of the max ROWID in pTab, or NULL if none
 **
 ** The 2nd register is the one that is returned.  That is all the
 ** insert routine needs to know about.
@@ -242,7 +243,7 @@ static int autoIncBegin(
       pInfo->iDb = iDb;
       pToplevel->nMem++;                  /* Register to hold name of table */
       pInfo->regCtr = ++pToplevel->nMem;  /* Max rowid register */
-      pToplevel->nMem++;                  /* Rowid in sqlite_sequence */
+      pToplevel->nMem +=2;       /* Rowid in sqlite_sequence + orig max val */
     }
     memId = pInfo->regCtr;
   }
@@ -270,15 +271,17 @@ void sqlite3AutoincrementBegin(Parse *pParse){
     static const int iLn = VDBE_OFFSET_LINENO(2);
     static const VdbeOpList autoInc[] = {
       /* 0  */ {OP_Null,    0,  0, 0},
-      /* 1  */ {OP_Rewind,  0,  9, 0},
+      /* 1  */ {OP_Rewind,  0, 10, 0},
       /* 2  */ {OP_Column,  0,  0, 0},
-      /* 3  */ {OP_Ne,      0,  7, 0},
+      /* 3  */ {OP_Ne,      0,  9, 0},
       /* 4  */ {OP_Rowid,   0,  0, 0},
       /* 5  */ {OP_Column,  0,  1, 0},
-      /* 6  */ {OP_Goto,    0,  9, 0},
-      /* 7  */ {OP_Next,    0,  2, 0},
-      /* 8  */ {OP_Integer, 0,  0, 0},
-      /* 9  */ {OP_Close,   0,  0, 0} 
+      /* 6  */ {OP_AddImm,  0,  0, 0},
+      /* 7  */ {OP_Copy,    0,  0, 0},
+      /* 8  */ {OP_Goto,    0, 11, 0},
+      /* 9  */ {OP_Next,    0,  2, 0},
+      /* 10 */ {OP_Integer, 0,  0, 0},
+      /* 11 */ {OP_Close,   0,  0, 0} 
     };
     VdbeOp *aOp;
     pDb = &db->aDb[p->iDb];
@@ -289,14 +292,17 @@ void sqlite3AutoincrementBegin(Parse *pParse){
     aOp = sqlite3VdbeAddOpList(v, ArraySize(autoInc), autoInc, iLn);
     if( aOp==0 ) break;
     aOp[0].p2 = memId;
-    aOp[0].p3 = memId+1;
+    aOp[0].p3 = memId+2;
     aOp[2].p3 = memId;
     aOp[3].p1 = memId-1;
     aOp[3].p3 = memId;
     aOp[3].p5 = SQLITE_JUMPIFNULL;
     aOp[4].p2 = memId+1;
     aOp[5].p3 = memId;
-    aOp[8].p2 = memId;
+    aOp[6].p1 = memId;
+    aOp[7].p2 = memId+2;
+    aOp[7].p1 = memId;
+    aOp[10].p2 = memId;
   }
 }
 
@@ -343,6 +349,8 @@ static SQLITE_NOINLINE void autoIncrementEnd(Parse *pParse){
 
     iRec = sqlite3GetTempReg(pParse);
     assert( sqlite3SchemaMutexHeld(db, 0, pDb->pSchema) );
+    sqlite3VdbeAddOp3(v, OP_Le, memId+2, sqlite3VdbeCurrentAddr(v)+7, memId);
+    VdbeCoverage(v);
     sqlite3OpenTable(pParse, 0, p->iDb, pDb->pSchema->pSeqTab, OP_OpenWrite);
     aOp = sqlite3VdbeAddOpList(v, ArraySize(autoIncEnd), autoIncEnd, iLn);
     if( aOp==0 ) break;