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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:Query or change the maximum number of worker threads allowed on each database connection separately using the "PRAGMA threads" command.
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Timelines: family | ancestors | descendants | both | threads
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SHA1: 29c5e8a7c9d7ce349a1e1d72082d23450e877b45
User & Date: drh 2014-08-25 15:13:22
Context
2014-08-25
22:43
Merge the CAST operator enhancements from trunk. check-in: 6c8f86e4 user: drh tags: threads
15:13
Query or change the maximum number of worker threads allowed on each database connection separately using the "PRAGMA threads" command. check-in: 29c5e8a7 user: drh tags: threads
13:27
Merge the recent performance enhancements implemented on trunk into the threads branch. check-in: dfdc900f user: drh tags: threads
Changes
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Changes to src/pragma.c.

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#define PragTyp_SHRINK_MEMORY                 26
#define PragTyp_SOFT_HEAP_LIMIT               27
#define PragTyp_STATS                         28
#define PragTyp_SYNCHRONOUS                   29
#define PragTyp_TABLE_INFO                    30
#define PragTyp_TEMP_STORE                    31
#define PragTyp_TEMP_STORE_DIRECTORY          32

#define PragTyp_WAL_AUTOCHECKPOINT            33
#define PragTyp_WAL_CHECKPOINT                34
#define PragTyp_ACTIVATE_EXTENSIONS           35
#define PragTyp_HEXKEY                        36
#define PragTyp_KEY                           37
#define PragTyp_REKEY                         38
#define PragTyp_LOCK_STATUS                   39
#define PragTyp_PARSER_TRACE                  40
#define PragFlag_NeedSchema           0x01
static const struct sPragmaNames {
  const char *const zName;  /* Name of pragma */
  u8 ePragTyp;              /* PragTyp_XXX value */
  u8 mPragFlag;             /* Zero or more PragFlag_XXX values */
  u32 iArg;                 /* Extra argument */
} aPragmaNames[] = {
................................................................................
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
  { /* zName:     */ "temp_store_directory",
    /* ePragTyp:  */ PragTyp_TEMP_STORE_DIRECTORY,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#endif




#if !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
  { /* zName:     */ "user_version",
    /* ePragTyp:  */ PragTyp_HEADER_VALUE,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#endif
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
................................................................................
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
  { /* zName:     */ "writable_schema",
    /* ePragTyp:  */ PragTyp_FLAG,
    /* ePragFlag: */ 0,
    /* iArg:      */ SQLITE_WriteSchema|SQLITE_RecoveryMode },
#endif
};
/* Number of pragmas: 56 on by default, 69 total. */
/* End of the automatically generated pragma table.
***************************************************************************/

/*
** Interpret the given string as a safety level.  Return 0 for OFF,
** 1 for ON or NORMAL and 2 for FULL.  Return 1 for an empty or 
** unrecognized string argument.  The FULL option is disallowed
................................................................................
    sqlite3_int64 N;
    if( zRight && sqlite3DecOrHexToI64(zRight, &N)==SQLITE_OK ){
      sqlite3_soft_heap_limit64(N);
    }
    returnSingleInt(pParse, "soft_heap_limit",  sqlite3_soft_heap_limit64(-1));
    break;
  }






















#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  /*
  ** Report the current state of file logs for all databases
  */
  case PragTyp_LOCK_STATUS: {
    static const char *const azLockName[] = {







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#define PragTyp_SHRINK_MEMORY                 26
#define PragTyp_SOFT_HEAP_LIMIT               27
#define PragTyp_STATS                         28
#define PragTyp_SYNCHRONOUS                   29
#define PragTyp_TABLE_INFO                    30
#define PragTyp_TEMP_STORE                    31
#define PragTyp_TEMP_STORE_DIRECTORY          32
#define PragTyp_THREADS                       33
#define PragTyp_WAL_AUTOCHECKPOINT            34
#define PragTyp_WAL_CHECKPOINT                35
#define PragTyp_ACTIVATE_EXTENSIONS           36
#define PragTyp_HEXKEY                        37
#define PragTyp_KEY                           38
#define PragTyp_REKEY                         39
#define PragTyp_LOCK_STATUS                   40
#define PragTyp_PARSER_TRACE                  41
#define PragFlag_NeedSchema           0x01
static const struct sPragmaNames {
  const char *const zName;  /* Name of pragma */
  u8 ePragTyp;              /* PragTyp_XXX value */
  u8 mPragFlag;             /* Zero or more PragFlag_XXX values */
  u32 iArg;                 /* Extra argument */
} aPragmaNames[] = {
................................................................................
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
  { /* zName:     */ "temp_store_directory",
    /* ePragTyp:  */ PragTyp_TEMP_STORE_DIRECTORY,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#endif
  { /* zName:     */ "threads",
    /* ePragTyp:  */ PragTyp_THREADS,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#if !defined(SQLITE_OMIT_SCHEMA_VERSION_PRAGMAS)
  { /* zName:     */ "user_version",
    /* ePragTyp:  */ PragTyp_HEADER_VALUE,
    /* ePragFlag: */ 0,
    /* iArg:      */ 0 },
#endif
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
................................................................................
#if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
  { /* zName:     */ "writable_schema",
    /* ePragTyp:  */ PragTyp_FLAG,
    /* ePragFlag: */ 0,
    /* iArg:      */ SQLITE_WriteSchema|SQLITE_RecoveryMode },
#endif
};
/* Number of pragmas: 57 on by default, 70 total. */
/* End of the automatically generated pragma table.
***************************************************************************/

/*
** Interpret the given string as a safety level.  Return 0 for OFF,
** 1 for ON or NORMAL and 2 for FULL.  Return 1 for an empty or 
** unrecognized string argument.  The FULL option is disallowed
................................................................................
    sqlite3_int64 N;
    if( zRight && sqlite3DecOrHexToI64(zRight, &N)==SQLITE_OK ){
      sqlite3_soft_heap_limit64(N);
    }
    returnSingleInt(pParse, "soft_heap_limit",  sqlite3_soft_heap_limit64(-1));
    break;
  }

  /*
  **   PRAGMA threads
  **   PRAGMA threads = N
  **
  ** Configure the maximum number of worker threads.  Return the new
  ** maximum, which might be less than requested.
  */
  case PragTyp_THREADS: {
    sqlite3_int64 N;
    if( sqlite3GlobalConfig.bCoreMutex
     && zRight
     && sqlite3DecOrHexToI64(zRight, &N)==SQLITE_OK
     && N>=0
    ){
      if( N>sqlite3GlobalConfig.nWorker ) N = sqlite3GlobalConfig.nWorker;
      db->mxWorker = N&0xff;
    }
    returnSingleInt(pParse, "soft_heap_limit",  db->mxWorker);
    break;
  }

#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  /*
  ** Report the current state of file logs for all databases
  */
  case PragTyp_LOCK_STATUS: {
    static const char *const azLockName[] = {

Changes to src/shell.c.

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  memset(data, 0, sizeof(*data));
  data->mode = MODE_List;
  memcpy(data->separator,"|", 2);
  memcpy(data->newline,"\r\n", 3);
  data->showHeader = 0;
  sqlite3_config(SQLITE_CONFIG_URI, 1);
  sqlite3_config(SQLITE_CONFIG_LOG, shellLog, data);


  sqlite3_snprintf(sizeof(mainPrompt), mainPrompt,"sqlite> ");
  sqlite3_snprintf(sizeof(continuePrompt), continuePrompt,"   ...> ");
  sqlite3_config(SQLITE_CONFIG_MULTITHREAD);
  sqlite3_config(SQLITE_CONFIG_WORKER_THREADS, 4);
}

/*
** Output text to the console in a font that attracts extra attention.
*/
#ifdef _WIN32
static void printBold(const char *zText){







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  memset(data, 0, sizeof(*data));
  data->mode = MODE_List;
  memcpy(data->separator,"|", 2);
  memcpy(data->newline,"\r\n", 3);
  data->showHeader = 0;
  sqlite3_config(SQLITE_CONFIG_URI, 1);
  sqlite3_config(SQLITE_CONFIG_LOG, shellLog, data);
  sqlite3_config(SQLITE_CONFIG_MULTITHREAD);
  sqlite3_config(SQLITE_CONFIG_WORKER_THREADS, 64);
  sqlite3_snprintf(sizeof(mainPrompt), mainPrompt,"sqlite> ");
  sqlite3_snprintf(sizeof(continuePrompt), continuePrompt,"   ...> ");


}

/*
** Output text to the console in a font that attracts extra attention.
*/
#ifdef _WIN32
static void printBold(const char *zText){

Changes to src/sqliteInt.h.

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  u8 temp_store;                /* 1: file 2: memory 0: default */
  u8 mallocFailed;              /* True if we have seen a malloc failure */
  u8 dfltLockMode;              /* Default locking-mode for attached dbs */
  signed char nextAutovac;      /* Autovac setting after VACUUM if >=0 */
  u8 suppressErr;               /* Do not issue error messages if true */
  u8 vtabOnConflict;            /* Value to return for s3_vtab_on_conflict() */
  u8 isTransactionSavepoint;    /* True if the outermost savepoint is a TS */

  int nextPagesize;             /* Pagesize after VACUUM if >0 */
  u32 magic;                    /* Magic number for detect library misuse */
  int nChange;                  /* Value returned by sqlite3_changes() */
  int nTotalChange;             /* Value returned by sqlite3_total_changes() */
  int aLimit[SQLITE_N_LIMIT];   /* Limits */
  int nMaxSorterMmap;           /* Maximum size of regions mapped by sorter */
  struct sqlite3InitInfo {      /* Information used during initialization */







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  u8 temp_store;                /* 1: file 2: memory 0: default */
  u8 mallocFailed;              /* True if we have seen a malloc failure */
  u8 dfltLockMode;              /* Default locking-mode for attached dbs */
  signed char nextAutovac;      /* Autovac setting after VACUUM if >=0 */
  u8 suppressErr;               /* Do not issue error messages if true */
  u8 vtabOnConflict;            /* Value to return for s3_vtab_on_conflict() */
  u8 isTransactionSavepoint;    /* True if the outermost savepoint is a TS */
  u8 mxWorker;                  /* Maximum number of worker threads */
  int nextPagesize;             /* Pagesize after VACUUM if >0 */
  u32 magic;                    /* Magic number for detect library misuse */
  int nChange;                  /* Value returned by sqlite3_changes() */
  int nTotalChange;             /* Value returned by sqlite3_total_changes() */
  int aLimit[SQLITE_N_LIMIT];   /* Limits */
  int nMaxSorterMmap;           /* Maximum size of regions mapped by sorter */
  struct sqlite3InitInfo {      /* Information used during initialization */

Changes to src/vdbesort.c.

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  VdbeSorter *pSorter;            /* The new sorter */
  KeyInfo *pKeyInfo;              /* Copy of pCsr->pKeyInfo with db==0 */
  int szKeyInfo;                  /* Size of pCsr->pKeyInfo in bytes */
  int sz;                         /* Size of pSorter in bytes */
  int rc = SQLITE_OK;
#if SQLITE_MAX_WORKER_THREADS==0
# define nWorker 0


#else
  int nWorker = (sqlite3GlobalConfig.bCoreMutex?sqlite3GlobalConfig.nWorker:0);

#endif

  assert( pCsr->pKeyInfo && pCsr->pBt==0 );
  szKeyInfo = sizeof(KeyInfo) + (pCsr->pKeyInfo->nField-1)*sizeof(CollSeq*);
  sz = sizeof(VdbeSorter) + nWorker * sizeof(SortSubtask);

  pSorter = (VdbeSorter*)sqlite3DbMallocZero(db, sz + szKeyInfo);







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  VdbeSorter *pSorter;            /* The new sorter */
  KeyInfo *pKeyInfo;              /* Copy of pCsr->pKeyInfo with db==0 */
  int szKeyInfo;                  /* Size of pCsr->pKeyInfo in bytes */
  int sz;                         /* Size of pSorter in bytes */
  int rc = SQLITE_OK;
#if SQLITE_MAX_WORKER_THREADS==0
# define nWorker 0
#elif SQLITE_MAX_WORKER_THREADS>=SORTER_MAX_MERGE_COUNT
  int nWorker = MIN(SORTER_MAX_MERGE_COUNT-1, db->mxWorker);
#else

  int nWorker = db->mxWorker;
#endif

  assert( pCsr->pKeyInfo && pCsr->pBt==0 );
  szKeyInfo = sizeof(KeyInfo) + (pCsr->pKeyInfo->nField-1)*sizeof(CollSeq*);
  sz = sizeof(VdbeSorter) + nWorker * sizeof(SortSubtask);

  pSorter = (VdbeSorter*)sqlite3DbMallocZero(db, sz + szKeyInfo);

Changes to tool/mkpragmatab.tcl.

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  TYPE: HEXKEY
  IF:   defined(SQLITE_HAS_CODEC)

  NAME: activate_extensions
  IF:   defined(SQLITE_HAS_CODEC) || defined(SQLITE_ENABLE_CEROD)

  NAME: soft_heap_limit


}
fconfigure stdout -translation lf
set name {}
set type {}
set if {}
set flags {}
set arg 0







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  TYPE: HEXKEY
  IF:   defined(SQLITE_HAS_CODEC)

  NAME: activate_extensions
  IF:   defined(SQLITE_HAS_CODEC) || defined(SQLITE_ENABLE_CEROD)

  NAME: soft_heap_limit

  NAME: threads
}
fconfigure stdout -translation lf
set name {}
set type {}
set if {}
set flags {}
set arg 0