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Overview
Comment:Update test program "tserver" to use a native pthreads mutex/condition variable to efficiently manage wal file checkpoints without the wal file growing indefinitely.
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Timelines: family | ancestors | descendants | both | server-process-edition
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SHA3-256:8299bdb7cbede30c665dda131bdcbd1d260b3ae9bd16d9b414d8c3776b08f1b3
User & Date: dan 2017-07-29 17:01:06
Context
2017-07-29
17:10
Merge latest trunk changes with this branch. check-in: b42c8779 user: dan tags: server-process-edition
17:01
Update test program "tserver" to use a native pthreads mutex/condition variable to efficiently manage wal file checkpoints without the wal file growing indefinitely. check-in: 8299bdb7 user: dan tags: server-process-edition
2017-07-28
21:02
Reduce the number of mallocs required of writers in server mode. check-in: 60953997 user: dan tags: server-process-edition
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/pager.c.

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int sqlite3PagerWalFramesize(Pager *pPager){
  assert( pPager->eState>=PAGER_READER );
  return sqlite3WalFramesize(pPager->pWal);
}
#endif

#ifdef SQLITE_SERVER_EDITION
int sqlite3PagerIsServer(Pager *pPager){
  return pagerIsServer(pPager);
}
int sqlite3PagerPagelock(Pager *pPager, Pgno pgno, int bWrite){
  if( pagerIsServer(pPager)==0 ) return SQLITE_OK;
  return sqlite3ServerLock(pPager->pServer, pgno, bWrite, 0);
}
#endif

#endif /* SQLITE_OMIT_DISKIO */







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int sqlite3PagerWalFramesize(Pager *pPager){
  assert( pPager->eState>=PAGER_READER );
  return sqlite3WalFramesize(pPager->pWal);
}
#endif

#ifdef SQLITE_SERVER_EDITION



int sqlite3PagerPagelock(Pager *pPager, Pgno pgno, int bWrite){
  if( pagerIsServer(pPager)==0 ) return SQLITE_OK;
  return sqlite3ServerLock(pPager->pServer, pgno, bWrite, 0);
}
#endif

#endif /* SQLITE_OMIT_DISKIO */

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#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

#ifdef SQLITE_SERVER_EDITION
  int sqlite3PagerRollbackJournal(Pager*, sqlite3_file*);
  int sqlite3PagerIsServer(Pager *pPager);
  int sqlite3PagerPagelock(Pager *pPager, Pgno, int);
  void sqlite3PagerServerJournal(Pager*, sqlite3_file*, const char*);
#endif

#endif /* SQLITE_PAGER_H */







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#else
# define disable_simulated_io_errors()
# define enable_simulated_io_errors()
#endif

#ifdef SQLITE_SERVER_EDITION
  int sqlite3PagerRollbackJournal(Pager*, sqlite3_file*);

  int sqlite3PagerPagelock(Pager *pPager, Pgno, int);
  void sqlite3PagerServerJournal(Pager*, sqlite3_file*, const char*);
#endif

#endif /* SQLITE_PAGER_H */

Changes to src/server.c.

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  if( pDb->nClient==0 ){
    ServerPage *pFree;
    ServerDb **pp;
    serverShutdownDatabase(pDb);
    for(pp=&g_server.pDb; *pp!=pDb; pp=&((*pp)->pNext));
    *pp = pDb->pNext;
    sqlite3_mutex_free(pDb->mutex);
    while( pFree=pDb->pFree ){
      pDb->pFree = pFree->pNext;
      sqlite3_free(pFree);
    }
    sqlite3_free(pDb);
  }
  serverLeaveMutex();








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  if( pDb->nClient==0 ){
    ServerPage *pFree;
    ServerDb **pp;
    serverShutdownDatabase(pDb);
    for(pp=&g_server.pDb; *pp!=pDb; pp=&((*pp)->pNext));
    *pp = pDb->pNext;
    sqlite3_mutex_free(pDb->mutex);
    while( (pFree = pDb->pFree) ){
      pDb->pFree = pFree->pNext;
      sqlite3_free(pFree);
    }
    sqlite3_free(pDb);
  }
  serverLeaveMutex();

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** Dot-commands are:
**
**   .list                    Display all SQL statements in the list.
**   .quit                    Disconnect.
**   .run                     Run all SQL statements in the list.
**   .repeats N               Configure the number of repeats per ".run".
**   .seconds N               Configure the number of seconds to ".run" for.


**
** Example input:
**
**   BEGIN;
**     INSERT INTO t1 VALUES(randomblob(10), randomblob(100));
**     INSERT INTO t1 VALUES(randomblob(10), randomblob(100));
**     INSERT INTO t1 VALUES(randomblob(10), randomblob(100));
................................................................................
#include <string.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <unistd.h>

#include "sqlite3.h"





/* Database used by this server */
static char *zDatabaseName = 0;



static char *zGlobalVfs = 0;


















typedef struct ClientCtx ClientCtx;
struct ClientCtx {
  sqlite3 *db;                    /* Database handle for this client */
  int fd;                         /* Client fd */
  int nRepeat;                    /* Number of times to repeat SQL */
  int nSecond;                    /* Number of seconds to run for */
  sqlite3_stmt **apPrepare;       /* Array of prepared statements */
  int nPrepare;                   /* Valid size of apPrepare[] */
  int nAlloc;                     /* Allocated size of apPrepare[] */
};

static int is_eol(int i){
  return (i=='\n' || i=='\r');
}
................................................................................
static int handle_some_sql(ClientCtx *p, const char *zSql, int nSql){
  const char *zTail = zSql;
  int nTail = nSql;
  int rc = SQLITE_OK;

  while( rc==SQLITE_OK ){
    if( p->nPrepare>=p->nAlloc ){
      int nByte = (p->nPrepare+32) * sizeof(sqlite3_stmt*);
      sqlite3_stmt **apNew = sqlite3_realloc(p->apPrepare, nByte);
      if( apNew ){

        p->apPrepare = apNew;
        p->nAlloc = p->nPrepare+32;
      }else{
        rc = SQLITE_NOMEM;
        break;
      }
    }
    rc = sqlite3_prepare_v2(
        p->db, zTail, nTail, &p->apPrepare[p->nPrepare], &zTail
    );
    if( rc!=SQLITE_OK ){
      send_message(p, "error - %s\n", sqlite3_errmsg(p->db));
      rc = 1;
      break;
    }
    if( p->apPrepare[p->nPrepare]==0 ){
      break;
    }
    p->nPrepare++;
    nTail = nSql - (zTail-zSql);
    rc = send_message(p, "ok (%d SQL statements)\n", p->nPrepare);
  }

................................................................................
  gettimeofday(&t, 0);
  return ((sqlite3_int64)t.tv_usec / 1000) + ((sqlite3_int64)t.tv_sec * 1000);
}

static void clear_sql(ClientCtx *p){
  int j;
  for(j=0; j<p->nPrepare; j++){
    sqlite3_finalize(p->apPrepare[j]);
  }
  p->nPrepare = 0;
}









































































































static int handle_dot_command(ClientCtx *p, const char *zCmd, int nCmd){
  assert( zCmd[0]=='.' );
  int n;
  int rc = 0;
  const char *z = &zCmd[1];
  const char *zArg;
  int nArg;


  for(n=0; n<(nCmd-1); n++){
    if( is_whitespace(z[n]) ) break;
  }

  zArg = &z[n];
  nArg = nCmd-n;
  trim_string(&zArg, &nArg);

  if( n>=1 && n<=4 && 0==strncmp(z, "list", n) ){
    int i;
    for(i=0; rc==0 && i<p->nPrepare; i++){
      const char *zSql = sqlite3_sql(p->apPrepare[i]);
      int nSql = strlen(zSql);
      trim_string(&zSql, &nSql);
      rc = send_message(p, "%d: %.*s\n", i, nSql, zSql);
    }
  }

  else if( n>=1 && n<=4 && 0==strncmp(z, "quit", n) ){
................................................................................
      p->nRepeat = strtol(zArg, 0, 0);
      if( p->nRepeat>0 ) p->nSecond = 0;
    }
    rc = send_message(p, "ok (repeat=%d)\n", p->nRepeat);
  }

  else if( n>=2 && n<=3 && 0==strncmp(z, "run", n) ){
    int i, j;
    int nBusy = 0;
    sqlite3_int64 t0 = get_timer();
    sqlite3_int64 t1 = t0;
    int nT1 = 0;
    int nTBusy1 = 0;

    for(j=0; (p->nRepeat<=0 || j<p->nRepeat) && rc==SQLITE_OK; j++){
      sqlite3_int64 t2;

      for(i=0; i<p->nPrepare && rc==SQLITE_OK; i++){
        sqlite3_stmt *pStmt = p->apPrepare[i];

        /* Execute the statement */
        while( sqlite3_step(pStmt)==SQLITE_ROW );
        rc = sqlite3_reset(pStmt);

        if( (rc & 0xFF)==SQLITE_BUSY ){
          if( sqlite3_get_autocommit(p->db)==0 ){
            sqlite3_exec(p->db, "ROLLBACK", 0, 0, 0);
          }
          nBusy++;
          rc = SQLITE_OK;
          break;
        }
        else if( rc!=SQLITE_OK ){
          send_message(p, "error - %s\n", sqlite3_errmsg(p->db));
        }
      }

      t2 = get_timer();
      if( t2>=(t1+1000) ){
        int nMs = (t2 - t1);
        int nDone = (j+1 - nBusy - nT1);

        rc = send_message(
            p, "(%d done @ %d per second, %d busy)\n", 
            nDone, (1000*nDone + nMs/2) / nMs, nBusy - nTBusy1
        );
        t1 = t2;
        nT1 = j+1 - nBusy;
        nTBusy1 = nBusy;
        if( p->nSecond>0 && (p->nSecond*1000)<=t1-t0 ) break;
      }
    }

    if( rc==SQLITE_OK ){
      send_message(p, "ok (%d/%d SQLITE_BUSY)\n", nBusy, j);
    }
    clear_sql(p);
  }

  else if( n>=1 && n<=7 && 0==strncmp(z, "seconds", n) ){
    if( nArg ){
      p->nSecond = strtol(zArg, 0, 0);
      if( p->nSecond>0 ) p->nRepeat = 0;
    }
    rc = send_message(p, "ok (repeat=%d)\n", p->nRepeat);
  }








  else{
    send_message(p, 
        "unrecognized dot command: %.*s\n"
        "should be \"list\", \"run\", \"repeats\", or \"seconds\"\n", n, z

    );
    rc = 1;
  }

  return rc;
}

................................................................................
  int rc = SQLITE_OK;

  ClientCtx ctx;
  memset(&ctx, 0, sizeof(ClientCtx));

  ctx.fd = (int)(intptr_t)pArg;
  ctx.nRepeat = 1;
  rc = sqlite3_open_v2(zDatabaseName, &ctx.db,
      SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE, zGlobalVfs
  );
  if( rc!=SQLITE_OK ){
    fprintf(stderr, "sqlite3_open(): %s\n", sqlite3_errmsg(ctx.db));
    return 0;
  }
  sqlite3_create_function(
      ctx.db, "usleep", 1, SQLITE_UTF8, (void*)sqlite3_vfs_find(0), 
      usleepFunc, 0, 0
  );




  while( rc==SQLITE_OK ){
    int i;
    int iStart;
    int nConsume;
    res = read(ctx.fd, &zCmd[nCmd], sizeof(zCmd)-nCmd-1);
    if( res<=0 ) break;
................................................................................
      }
    }while( rc==SQLITE_OK && nConsume>0 );
  }

  fprintf(stdout, "Client %d disconnects\n", ctx.fd);
  close(ctx.fd);
  clear_sql(&ctx);
  sqlite3_free(ctx.apPrepare);
  sqlite3_close(ctx.db);
  return 0;
} 

static void usage(const char *zExec){
  fprintf(stderr, "Usage: %s ?-vfs VFS? DATABASE\n", zExec);
  exit(1);
................................................................................

  if( argc!=2 && argc!=4 ){
    usage(argv[0]);
  }
  if( argc==4 ){
    int n = strlen(argv[1]);
    if( n<2 || n>4 || memcmp("-vfs", argv[1], 4) ) usage(argv[0]);
    zGlobalVfs = argv[2];
  }
  zDatabaseName = argv[argc-1];






  rc = sqlite3_open_v2(zDatabaseName, &db,
      SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE, zGlobalVfs
  );
  if( rc!=SQLITE_OK ){
    fprintf(stderr, "sqlite3_open(): %s\n", sqlite3_errmsg(db));
    return 1;
  }

  rc = sqlite3_exec(db, "SELECT * FROM sqlite_master", 0, 0, 0);







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** Dot-commands are:
**
**   .list                    Display all SQL statements in the list.
**   .quit                    Disconnect.
**   .run                     Run all SQL statements in the list.
**   .repeats N               Configure the number of repeats per ".run".
**   .seconds N               Configure the number of seconds to ".run" for.
**   .mutex_commit            Add a "COMMIT" protected by a g.commit_mutex
**                            to the current SQL.
**
** Example input:
**
**   BEGIN;
**     INSERT INTO t1 VALUES(randomblob(10), randomblob(100));
**     INSERT INTO t1 VALUES(randomblob(10), randomblob(100));
**     INSERT INTO t1 VALUES(randomblob(10), randomblob(100));
................................................................................
#include <string.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <unistd.h>

#include "sqlite3.h"

#define TSERVER_DEFAULT_CHECKPOINT_THRESHOLD 3900

/* Global variables */
struct TserverGlobal {
  char *zDatabaseName;             /* Database used by this server */

  char *zVfs;
  sqlite3_mutex *commit_mutex;


  /* The following use native pthreads instead of a portable interface. This
  ** is because a condition variable, as well as a mutex, is required.  */
  pthread_mutex_t ckpt_mutex;
  pthread_cond_t ckpt_cond;
  int nThreshold;                  /* Checkpoint when wal is this large */
  int bCkptRequired;               /* True if wal checkpoint is required */
  int nRun;                        /* Number of clients in ".run" */
  int nWait;                       /* Number of clients waiting on ckpt_cond */
};

static struct TserverGlobal g = {0};

typedef struct ClientSql ClientSql;
struct ClientSql {
  sqlite3_stmt *pStmt;
  int bMutex;
};

typedef struct ClientCtx ClientCtx;
struct ClientCtx {
  sqlite3 *db;                    /* Database handle for this client */
  int fd;                         /* Client fd */
  int nRepeat;                    /* Number of times to repeat SQL */
  int nSecond;                    /* Number of seconds to run for */
  ClientSql *aPrepare;            /* Array of prepared statements */
  int nPrepare;                   /* Valid size of apPrepare[] */
  int nAlloc;                     /* Allocated size of apPrepare[] */
};

static int is_eol(int i){
  return (i=='\n' || i=='\r');
}
................................................................................
static int handle_some_sql(ClientCtx *p, const char *zSql, int nSql){
  const char *zTail = zSql;
  int nTail = nSql;
  int rc = SQLITE_OK;

  while( rc==SQLITE_OK ){
    if( p->nPrepare>=p->nAlloc ){
      int nByte = (p->nPrepare+32) * sizeof(ClientSql);
      ClientSql *aNew = sqlite3_realloc(p->aPrepare, nByte);
      if( aNew ){
        memset(&aNew[p->nPrepare], 0, sizeof(ClientSql)*32);
        p->aPrepare = aNew;
        p->nAlloc = p->nPrepare+32;
      }else{
        rc = SQLITE_NOMEM;
        break;
      }
    }
    rc = sqlite3_prepare_v2(
        p->db, zTail, nTail, &p->aPrepare[p->nPrepare].pStmt, &zTail
    );
    if( rc!=SQLITE_OK ){
      send_message(p, "error - %s\n", sqlite3_errmsg(p->db));
      rc = 1;
      break;
    }
    if( p->aPrepare[p->nPrepare].pStmt==0 ){
      break;
    }
    p->nPrepare++;
    nTail = nSql - (zTail-zSql);
    rc = send_message(p, "ok (%d SQL statements)\n", p->nPrepare);
  }

................................................................................
  gettimeofday(&t, 0);
  return ((sqlite3_int64)t.tv_usec / 1000) + ((sqlite3_int64)t.tv_sec * 1000);
}

static void clear_sql(ClientCtx *p){
  int j;
  for(j=0; j<p->nPrepare; j++){
    sqlite3_finalize(p->aPrepare[j].pStmt);
  }
  p->nPrepare = 0;
}

/*
** The sqlite3_wal_hook() callback used by all client database connections.
*/
static int clientWalHook(void *pArg, sqlite3 *db, const char *zDb, int nFrame){
  if( nFrame>=g.nThreshold ){
    g.bCkptRequired = 1;
  }
  return SQLITE_OK;
}

static int handle_run_command(ClientCtx *p){
  int i, j;
  int nBusy = 0;
  sqlite3_int64 t0 = get_timer();
  sqlite3_int64 t1 = t0;
  int nT1 = 0;
  int nTBusy1 = 0;
  int rc = SQLITE_OK;

  pthread_mutex_lock(&g.ckpt_mutex);
  g.nRun++;
  pthread_mutex_unlock(&g.ckpt_mutex);


  for(j=0; (p->nRepeat<=0 || j<p->nRepeat) && rc==SQLITE_OK; j++){
    sqlite3_int64 t2;

    for(i=0; i<p->nPrepare && rc==SQLITE_OK; i++){
      sqlite3_stmt *pStmt = p->aPrepare[i].pStmt;

      /* If the bMutex flag is set, grab g.commit_mutex before executing
      ** the SQL statement (which is always "COMMIT" in this case). */
      if( p->aPrepare[i].bMutex ){
        sqlite3_mutex_enter(g.commit_mutex);
      }

      /* Execute the statement */
      while( sqlite3_step(pStmt)==SQLITE_ROW );
      rc = sqlite3_reset(pStmt);

      /* Relinquish the g.commit_mutex mutex if required. */
      if( p->aPrepare[i].bMutex ){
        sqlite3_mutex_leave(g.commit_mutex);
      }

      if( (rc & 0xFF)==SQLITE_BUSY ){
        if( sqlite3_get_autocommit(p->db)==0 ){
          sqlite3_exec(p->db, "ROLLBACK", 0, 0, 0);
        }
        nBusy++;
        rc = SQLITE_OK;
        break;
      }
      else if( rc!=SQLITE_OK ){
        send_message(p, "error - %s\n", sqlite3_errmsg(p->db));
      }
    }

    t2 = get_timer();
    if( t2>=(t1+1000) ){
      int nMs = (t2 - t1);
      int nDone = (j+1 - nBusy - nT1);

      rc = send_message(
          p, "(%d done @ %d per second, %d busy)\n", 
          nDone, (1000*nDone + nMs/2) / nMs, nBusy - nTBusy1
          );
      t1 = t2;
      nT1 = j+1 - nBusy;
      nTBusy1 = nBusy;
      if( p->nSecond>0 && (p->nSecond*1000)<=t1-t0 ) break;
    }

    /* Checkpoint handling. */
    pthread_mutex_lock(&g.ckpt_mutex);
    if( rc==SQLITE_OK && g.bCkptRequired ){
      if( g.nWait==g.nRun-1 ){
        /* All other clients are already waiting on the condition variable.
        ** Run the checkpoint, signal the condition and move on.  */
        rc = sqlite3_wal_checkpoint(p->db, "main");
        g.bCkptRequired = 0;
        pthread_cond_broadcast(&g.ckpt_cond);
      }else{
        assert( g.nWait<g.nRun-1 );
        g.nWait++;
        pthread_cond_wait(&g.ckpt_cond, &g.ckpt_mutex);
        g.nWait--;
      }
    }
    pthread_mutex_unlock(&g.ckpt_mutex);
  }

  if( rc==SQLITE_OK ){
    send_message(p, "ok (%d/%d SQLITE_BUSY)\n", nBusy, j);
  }
  clear_sql(p);

  pthread_mutex_lock(&g.ckpt_mutex);
  g.nRun--;
  pthread_mutex_unlock(&g.ckpt_mutex);

  return rc;
}

static int handle_dot_command(ClientCtx *p, const char *zCmd, int nCmd){

  int n;
  int rc = 0;
  const char *z = &zCmd[1];
  const char *zArg;
  int nArg;

  assert( zCmd[0]=='.' );
  for(n=0; n<(nCmd-1); n++){
    if( is_whitespace(z[n]) ) break;
  }

  zArg = &z[n];
  nArg = nCmd-n;
  trim_string(&zArg, &nArg);

  if( n>=1 && n<=4 && 0==strncmp(z, "list", n) ){
    int i;
    for(i=0; rc==0 && i<p->nPrepare; i++){
      const char *zSql = sqlite3_sql(p->aPrepare[i].pStmt);
      int nSql = strlen(zSql);
      trim_string(&zSql, &nSql);
      rc = send_message(p, "%d: %.*s\n", i, nSql, zSql);
    }
  }

  else if( n>=1 && n<=4 && 0==strncmp(z, "quit", n) ){
................................................................................
      p->nRepeat = strtol(zArg, 0, 0);
      if( p->nRepeat>0 ) p->nSecond = 0;
    }
    rc = send_message(p, "ok (repeat=%d)\n", p->nRepeat);
  }

  else if( n>=2 && n<=3 && 0==strncmp(z, "run", n) ){
    rc = handle_run_command(p);

















































  }

  else if( n>=1 && n<=7 && 0==strncmp(z, "seconds", n) ){
    if( nArg ){
      p->nSecond = strtol(zArg, 0, 0);
      if( p->nSecond>0 ) p->nRepeat = 0;
    }
    rc = send_message(p, "ok (repeat=%d)\n", p->nRepeat);
  }

  else if( n>=1 && n<=12 && 0==strncmp(z, "mutex_commit", n) ){
    rc = handle_some_sql(p, "COMMIT;", 7);
    if( rc==SQLITE_OK ){
      p->aPrepare[p->nPrepare-1].bMutex = 1;
    }
  }

  else{
    send_message(p, 
        "unrecognized dot command: %.*s\n"
        "should be \"list\", \"run\", \"repeats\", \"mutex_commit\" "
        "or \"seconds\"\n", n, z
    );
    rc = 1;
  }

  return rc;
}

................................................................................
  int rc = SQLITE_OK;

  ClientCtx ctx;
  memset(&ctx, 0, sizeof(ClientCtx));

  ctx.fd = (int)(intptr_t)pArg;
  ctx.nRepeat = 1;
  rc = sqlite3_open_v2(g.zDatabaseName, &ctx.db,
      SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE, g.zVfs
  );
  if( rc!=SQLITE_OK ){
    fprintf(stderr, "sqlite3_open(): %s\n", sqlite3_errmsg(ctx.db));
    return 0;
  }
  sqlite3_create_function(
      ctx.db, "usleep", 1, SQLITE_UTF8, (void*)sqlite3_vfs_find(0), 
      usleepFunc, 0, 0
  );

  /* Register the wal-hook with the new client connection */
  sqlite3_wal_hook(ctx.db, clientWalHook, (void*)&ctx);

  while( rc==SQLITE_OK ){
    int i;
    int iStart;
    int nConsume;
    res = read(ctx.fd, &zCmd[nCmd], sizeof(zCmd)-nCmd-1);
    if( res<=0 ) break;
................................................................................
      }
    }while( rc==SQLITE_OK && nConsume>0 );
  }

  fprintf(stdout, "Client %d disconnects\n", ctx.fd);
  close(ctx.fd);
  clear_sql(&ctx);
  sqlite3_free(ctx.aPrepare);
  sqlite3_close(ctx.db);
  return 0;
} 

static void usage(const char *zExec){
  fprintf(stderr, "Usage: %s ?-vfs VFS? DATABASE\n", zExec);
  exit(1);
................................................................................

  if( argc!=2 && argc!=4 ){
    usage(argv[0]);
  }
  if( argc==4 ){
    int n = strlen(argv[1]);
    if( n<2 || n>4 || memcmp("-vfs", argv[1], 4) ) usage(argv[0]);
    g.zVfs = argv[2];
  }
  g.zDatabaseName = argv[argc-1];
  g.commit_mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);

  g.nThreshold = TSERVER_DEFAULT_CHECKPOINT_THRESHOLD;
  pthread_mutex_init(&g.ckpt_mutex, 0);
  pthread_cond_init(&g.ckpt_cond, 0);

  rc = sqlite3_open_v2(g.zDatabaseName, &db,
      SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE, g.zVfs
  );
  if( rc!=SQLITE_OK ){
    fprintf(stderr, "sqlite3_open(): %s\n", sqlite3_errmsg(db));
    return 1;
  }

  rc = sqlite3_exec(db, "SELECT * FROM sqlite_master", 0, 0, 0);