Index: src/pragma.c
==================================================================
--- src/pragma.c
+++ src/pragma.c
@@ -59,18 +59,19 @@
 #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 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 */
@@ -416,10 +417,14 @@
   { /* 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 },
@@ -463,11 +468,11 @@
     /* ePragTyp:  */ PragTyp_FLAG,
     /* ePragFlag: */ 0,
     /* iArg:      */ SQLITE_WriteSchema|SQLITE_RecoveryMode },
 #endif
 };
-/* Number of pragmas: 56 on by default, 69 total. */
+/* 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,
@@ -2270,10 +2275,31 @@
       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
   */

Index: src/shell.c
==================================================================
--- src/shell.c
+++ src/shell.c
@@ -3815,14 +3815,14 @@
   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,"   ...> ");
-  sqlite3_config(SQLITE_CONFIG_MULTITHREAD);
-  sqlite3_config(SQLITE_CONFIG_WORKER_THREADS, 4);
 }
 
 /*
 ** Output text to the console in a font that attracts extra attention.
 */

Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -1010,10 +1010,11 @@
   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 */

Index: src/vdbesort.c
==================================================================
--- src/vdbesort.c
+++ src/vdbesort.c
@@ -793,12 +793,14 @@
   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 = (sqlite3GlobalConfig.bCoreMutex?sqlite3GlobalConfig.nWorker:0);
+  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);

Index: tool/mkpragmatab.tcl
==================================================================
--- tool/mkpragmatab.tcl
+++ tool/mkpragmatab.tcl
@@ -292,10 +292,12 @@
 
   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 {}