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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Faster allocation of new sqlite3_stmt objects.
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Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA3-256: 891f1f72187f0f9ec0d24fda98cc08be3ae3c3ff8b27c4e409ee7135c3106398
User & Date: drh 2018-12-28 20:48:07
Context
2018-12-29
02:26
A new implementation of sqlite3VdbeMakeLabel() is faster and makes fewer memory allocations by deferring memory allocation until sqlite3VdbeResolveLabel() is called, at which point the code generator has a better idea of how big the relocation table needs to be. The sqlite3VdbeMakeLabel() routine now takes a Parse* parameter instead of Vdbe*. check-in: 4a0929ac user: drh tags: trunk
2018-12-28
21:32
Merge performance enhancements from trunk. check-in: 0f1b9ff9 user: drh tags: reuse-subqueries
20:48
Faster allocation of new sqlite3_stmt objects. check-in: 891f1f72 user: drh tags: trunk
20:14
Move the nOpAlloc field from Parse into Vdbe to avoid an extra pointer deference on the fast path in sqlite3VdbeAddOp3(). check-in: 8f10efc2 user: drh tags: trunk
Changes
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Changes to src/vdbeInt.h.

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  int rc;                 /* Value to return */
  int nChange;            /* Number of db changes made since last reset */
  int iStatement;         /* Statement number (or 0 if has no opened stmt) */
  i64 iCurrentTime;       /* Value of julianday('now') for this statement */
  i64 nFkConstraint;      /* Number of imm. FK constraints this VM */
  i64 nStmtDefCons;       /* Number of def. constraints when stmt started */
  i64 nStmtDefImmCons;    /* Number of def. imm constraints when stmt started */





  /* When allocating a new Vdbe object, all of the fields below should be
  ** initialized to zero or NULL */

  Op *aOp;                /* Space to hold the virtual machine's program */
  int nOp;                /* Number of instructions in the program */
  int nOpAlloc;           /* Slots allocated for aOp[] */
  Mem *aMem;              /* The memory locations */
  Mem **apArg;            /* Arguments to currently executing user function */
  Mem *aColName;          /* Column names to return */
  Mem *pResultSet;        /* Pointer to an array of results */
  char *zErrMsg;          /* Error message written here */
  VdbeCursor **apCsr;     /* One element of this array for each open cursor */
  Mem *aVar;              /* Values for the OP_Variable opcode. */
  VList *pVList;          /* Name of variables */
#ifndef SQLITE_OMIT_TRACE
  i64 startTime;          /* Time when query started - used for profiling */
#endif
#ifdef SQLITE_DEBUG
  int rcApp;              /* errcode set by sqlite3_result_error_code() */
  u32 nWrite;             /* Number of write operations that have occurred */







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  int rc;                 /* Value to return */
  int nChange;            /* Number of db changes made since last reset */
  int iStatement;         /* Statement number (or 0 if has no opened stmt) */
  i64 iCurrentTime;       /* Value of julianday('now') for this statement */
  i64 nFkConstraint;      /* Number of imm. FK constraints this VM */
  i64 nStmtDefCons;       /* Number of def. constraints when stmt started */
  i64 nStmtDefImmCons;    /* Number of def. imm constraints when stmt started */
  Mem *aMem;              /* The memory locations */
  Mem **apArg;            /* Arguments to currently executing user function */
  VdbeCursor **apCsr;     /* One element of this array for each open cursor */
  Mem *aVar;              /* Values for the OP_Variable opcode. */

  /* When allocating a new Vdbe object, all of the fields below should be
  ** initialized to zero or NULL */

  Op *aOp;                /* Space to hold the virtual machine's program */
  int nOp;                /* Number of instructions in the program */
  int nOpAlloc;           /* Slots allocated for aOp[] */


  Mem *aColName;          /* Column names to return */
  Mem *pResultSet;        /* Pointer to an array of results */
  char *zErrMsg;          /* Error message written here */


  VList *pVList;          /* Name of variables */
#ifndef SQLITE_OMIT_TRACE
  i64 startTime;          /* Time when query started - used for profiling */
#endif
#ifdef SQLITE_DEBUG
  int rcApp;              /* errcode set by sqlite3_result_error_code() */
  u32 nWrite;             /* Number of write operations that have occurred */

Changes to src/vdbeaux.c.

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  ** requirements by reusing the opcode array tail, then the second
  ** pass will fill in the remainder using a fresh memory allocation.  
  **
  ** This two-pass approach that reuses as much memory as possible from
  ** the leftover memory at the end of the opcode array.  This can significantly
  ** reduce the amount of memory held by a prepared statement.
  */
  do {
    x.nNeeded = 0;
    p->aMem = allocSpace(&x, p->aMem, nMem*sizeof(Mem));
    p->aVar = allocSpace(&x, p->aVar, nVar*sizeof(Mem));
    p->apArg = allocSpace(&x, p->apArg, nArg*sizeof(Mem*));
    p->apCsr = allocSpace(&x, p->apCsr, nCursor*sizeof(VdbeCursor*));
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
    p->anExec = allocSpace(&x, p->anExec, p->nOp*sizeof(i64));
#endif
    if( x.nNeeded==0 ) break;
    x.pSpace = p->pFree = sqlite3DbMallocRawNN(db, x.nNeeded);
    x.nFree = x.nNeeded;
  }while( !db->mallocFailed );










  p->pVList = pParse->pVList;
  pParse->pVList =  0;
  p->explain = pParse->explain;
  if( db->mallocFailed ){
    p->nVar = 0;
    p->nCursor = 0;







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  ** requirements by reusing the opcode array tail, then the second
  ** pass will fill in the remainder using a fresh memory allocation.  
  **
  ** This two-pass approach that reuses as much memory as possible from
  ** the leftover memory at the end of the opcode array.  This can significantly
  ** reduce the amount of memory held by a prepared statement.
  */

  x.nNeeded = 0;
  p->aMem = allocSpace(&x, 0, nMem*sizeof(Mem));
  p->aVar = allocSpace(&x, 0, nVar*sizeof(Mem));
  p->apArg = allocSpace(&x, 0, nArg*sizeof(Mem*));
  p->apCsr = allocSpace(&x, 0, nCursor*sizeof(VdbeCursor*));
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
  p->anExec = allocSpace(&x, 0, p->nOp*sizeof(i64));
#endif
  if( x.nNeeded ){
    x.pSpace = p->pFree = sqlite3DbMallocRawNN(db, x.nNeeded);
    x.nFree = x.nNeeded;
    if( !db->mallocFailed ){
      p->aMem = allocSpace(&x, p->aMem, nMem*sizeof(Mem));
      p->aVar = allocSpace(&x, p->aVar, nVar*sizeof(Mem));
      p->apArg = allocSpace(&x, p->apArg, nArg*sizeof(Mem*));
      p->apCsr = allocSpace(&x, p->apCsr, nCursor*sizeof(VdbeCursor*));
#ifdef SQLITE_ENABLE_STMT_SCANSTATUS
      p->anExec = allocSpace(&x, p->anExec, p->nOp*sizeof(i64));
#endif
    }
  }

  p->pVList = pParse->pVList;
  pParse->pVList =  0;
  p->explain = pParse->explain;
  if( db->mallocFailed ){
    p->nVar = 0;
    p->nCursor = 0;