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Overview
Comment:Avoid writing the sqlite_sequence table when it has not actually changed.
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SHA3-256: 3e3849a9d1a06673e6c713a42194f5da339fbf6533fa418c38f63d09bc045867
User & Date: drh 2018-03-16 18:46:30
Context
2018-03-20
13:44
Avoid unnecessary write to the sqlite_sequence table when an insert is done into an autoincrement table with an application-specified rowid that is less than the maximum. check-in: ec7addc8 user: drh tags: trunk
2018-03-16
18:46
Avoid writing the sqlite_sequence table when it has not actually changed. Closed-Leaf check-in: 3e3849a9 user: drh tags: autoinc-enhancement
07:48
Fix a problem in test script thread001.test causing a spurious "-1 files were left open" error when run separately. check-in: 1774f1c3 user: dan tags: trunk
Changes
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Changes to src/insert.c.

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**
** There is at most one AutoincInfo structure per table even if the
** same table is autoincremented multiple times due to inserts within
** triggers.  A new AutoincInfo structure is created if this is the
** first use of table pTab.  On 2nd and subsequent uses, the original
** AutoincInfo structure is used.
**
** Three memory locations 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

**
** The 2nd register is the one that is returned.  That is all the
** insert routine needs to know about.
*/
static int autoIncBegin(
  Parse *pParse,      /* Parsing context */
  int iDb,            /* Index of the database holding pTab */
................................................................................
      if( pInfo==0 ) return 0;
      pInfo->pNext = pToplevel->pAinc;
      pToplevel->pAinc = pInfo;
      pInfo->pTab = pTab;
      pInfo->iDb = iDb;
      pToplevel->nMem++;                  /* Register to hold name of table */
      pInfo->regCtr = ++pToplevel->nMem;  /* Max rowid register */
      pToplevel->nMem++;                  /* Rowid in sqlite_sequence */
    }
    memId = pInfo->regCtr;
  }
  return memId;
}

/*
................................................................................
  assert( sqlite3IsToplevel(pParse) );

  assert( v );   /* We failed long ago if this is not so */
  for(p = pParse->pAinc; p; p = p->pNext){
    static const int iLn = VDBE_OFFSET_LINENO(2);
    static const VdbeOpList autoInc[] = {
      /* 0  */ {OP_Null,    0,  0, 0},
      /* 1  */ {OP_Rewind,  0,  9, 0},
      /* 2  */ {OP_Column,  0,  0, 0},
      /* 3  */ {OP_Ne,      0,  7, 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} 
    };
    VdbeOp *aOp;
    pDb = &db->aDb[p->iDb];
    memId = p->regCtr;
    assert( sqlite3SchemaMutexHeld(db, 0, pDb->pSchema) );
    sqlite3OpenTable(pParse, 0, p->iDb, pDb->pSchema->pSeqTab, OP_OpenRead);
    sqlite3VdbeLoadString(v, memId-1, p->pTab->zName);
    aOp = sqlite3VdbeAddOpList(v, ArraySize(autoInc), autoInc, iLn);
    if( aOp==0 ) break;
    aOp[0].p2 = memId;
    aOp[0].p3 = memId+1;
    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;
  }
}

/*
** Update the maximum rowid for an autoincrement calculation.
**
** This routine should be called when the regRowid register holds a
................................................................................
    VdbeOp *aOp;
    Db *pDb = &db->aDb[p->iDb];
    int iRec;
    int memId = p->regCtr;

    iRec = sqlite3GetTempReg(pParse);
    assert( sqlite3SchemaMutexHeld(db, 0, pDb->pSchema) );


    sqlite3OpenTable(pParse, 0, p->iDb, pDb->pSchema->pSeqTab, OP_OpenWrite);
    aOp = sqlite3VdbeAddOpList(v, ArraySize(autoIncEnd), autoIncEnd, iLn);
    if( aOp==0 ) break;
    aOp[0].p1 = memId+1;
    aOp[1].p2 = memId+1;
    aOp[2].p1 = memId-1;
    aOp[2].p3 = iRec;







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**
** There is at most one AutoincInfo structure per table even if the
** same table is autoincremented multiple times due to inserts within
** triggers.  A new AutoincInfo structure is created if this is the
** first use of table pTab.  On 2nd and subsequent uses, the original
** AutoincInfo structure is used.
**
** Four consecutive registers are allocated:
**
**   (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.
*/
static int autoIncBegin(
  Parse *pParse,      /* Parsing context */
  int iDb,            /* Index of the database holding pTab */
................................................................................
      if( pInfo==0 ) return 0;
      pInfo->pNext = pToplevel->pAinc;
      pToplevel->pAinc = pInfo;
      pInfo->pTab = pTab;
      pInfo->iDb = iDb;
      pToplevel->nMem++;                  /* Register to hold name of table */
      pInfo->regCtr = ++pToplevel->nMem;  /* Max rowid register */
      pToplevel->nMem +=2;       /* Rowid in sqlite_sequence + orig max val */
    }
    memId = pInfo->regCtr;
  }
  return memId;
}

/*
................................................................................
  assert( sqlite3IsToplevel(pParse) );

  assert( v );   /* We failed long ago if this is not so */
  for(p = pParse->pAinc; p; p = p->pNext){
    static const int iLn = VDBE_OFFSET_LINENO(2);
    static const VdbeOpList autoInc[] = {
      /* 0  */ {OP_Null,    0,  0, 0},
      /* 1  */ {OP_Rewind,  0, 10, 0},
      /* 2  */ {OP_Column,  0,  0, 0},
      /* 3  */ {OP_Ne,      0,  9, 0},
      /* 4  */ {OP_Rowid,   0,  0, 0},
      /* 5  */ {OP_Column,  0,  1, 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];
    memId = p->regCtr;
    assert( sqlite3SchemaMutexHeld(db, 0, pDb->pSchema) );
    sqlite3OpenTable(pParse, 0, p->iDb, pDb->pSchema->pSeqTab, OP_OpenRead);
    sqlite3VdbeLoadString(v, memId-1, p->pTab->zName);
    aOp = sqlite3VdbeAddOpList(v, ArraySize(autoInc), autoInc, iLn);
    if( aOp==0 ) break;
    aOp[0].p2 = memId;
    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[6].p1 = memId;
    aOp[7].p2 = memId+2;
    aOp[7].p1 = memId;
    aOp[10].p2 = memId;
  }
}

/*
** Update the maximum rowid for an autoincrement calculation.
**
** This routine should be called when the regRowid register holds a
................................................................................
    VdbeOp *aOp;
    Db *pDb = &db->aDb[p->iDb];
    int iRec;
    int memId = p->regCtr;

    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;
    aOp[0].p1 = memId+1;
    aOp[1].p2 = memId+1;
    aOp[2].p1 = memId-1;
    aOp[2].p3 = iRec;