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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:Ignore the *-wal2 file if the *-wal file is zero bytes in size.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | wal2
Files: files | file ages | folders
SHA3-256: f7360fad51f224f347bb7d263eb89056b27461c278309e00e575a0e8898c9f40
User & Date: dan 2017-10-07 19:55:37
Wiki:wal2
Context
2017-10-09
19:49
Add a header comment to wal.c describing the differences between wal and wal2 mode. check-in: 9c80cd20 user: dan tags: wal2
2017-10-07
19:55
Ignore the *-wal2 file if the *-wal file is zero bytes in size. check-in: f7360fad user: dan tags: wal2
13:37
Check in test file wal2simple.test. check-in: 8932b2f1 user: dan tags: wal2
Changes
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Changes to src/wal.c.

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  int rc = SQLITE_OK;
  if( !isOpen(pWal->apWalFd[1]) ){
    int f = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
    rc = sqlite3OsOpen(pWal->pVfs, pWal->zWalName2, pWal->apWalFd[1], f, &f);
  }
  return rc;
}
















/*
** Recover the wal-index by reading the write-ahead log file. 
**
** This routine first tries to establish an exclusive lock on the
** wal-index to prevent other threads/processes from doing anything
** with the WAL or wal-index while recovery is running.  The
................................................................................
  ** pWal->hdr is already populated.
  */
  rc = walIndexRecoverOne(pWal, 0, &nCkpt1, &bZero);
  assert( pWal->hdr.iVersion==0 
      || pWal->hdr.iVersion==WAL_VERSION1 
      || pWal->hdr.iVersion==WAL_VERSION2 
  );



  if( rc==SQLITE_OK && pWal->hdr.iVersion!=WAL_VERSION1 ){
    int bOpen = 1;
    sqlite3_vfs *pVfs = pWal->pVfs;
    if( pWal->hdr.iVersion==0 && pWal->bWal2==0 ){
      rc = sqlite3OsAccess(pVfs, pWal->zWalName2, SQLITE_ACCESS_EXISTS, &bOpen);
    }
    if( rc==SQLITE_OK && bOpen ){
................................................................................
      }else

      /* Fallback */
      if( nCkpt1<=nCkpt2 ){
        pWal->hdr = hdr;
      }else{
        walidxSetFile(&pWal->hdr, 1);


      }
      pWal->hdr.iVersion = WAL_VERSION2;
    }else{
      pWal->hdr.iVersion = WAL_VERSION1;
    }

    walIndexWriteHdr(pWal);







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  int rc = SQLITE_OK;
  if( !isOpen(pWal->apWalFd[1]) ){
    int f = (SQLITE_OPEN_READWRITE|SQLITE_OPEN_CREATE|SQLITE_OPEN_WAL);
    rc = sqlite3OsOpen(pWal->pVfs, pWal->zWalName2, pWal->apWalFd[1], f, &f);
  }
  return rc;
}

static int walTruncateWal2(Wal *pWal){
  int bIs;
  int rc;
  assert( !isOpen(pWal->apWalFd[1]) );
  rc = sqlite3OsAccess(pWal->pVfs, pWal->zWalName2, SQLITE_ACCESS_EXISTS, &bIs);
  if( rc==SQLITE_OK && bIs ){
    rc = walOpenWal2(pWal);
    if( rc==SQLITE_OK ){
      rc = sqlite3OsTruncate(pWal->apWalFd[1], 0);
      sqlite3OsClose(pWal->apWalFd[1]);
    }
  }
  return rc;
}

/*
** Recover the wal-index by reading the write-ahead log file. 
**
** This routine first tries to establish an exclusive lock on the
** wal-index to prevent other threads/processes from doing anything
** with the WAL or wal-index while recovery is running.  The
................................................................................
  ** pWal->hdr is already populated.
  */
  rc = walIndexRecoverOne(pWal, 0, &nCkpt1, &bZero);
  assert( pWal->hdr.iVersion==0 
      || pWal->hdr.iVersion==WAL_VERSION1 
      || pWal->hdr.iVersion==WAL_VERSION2 
  );
  if( rc==SQLITE_OK && bZero ){
    rc = walTruncateWal2(pWal);
  }
  if( rc==SQLITE_OK && pWal->hdr.iVersion!=WAL_VERSION1 ){
    int bOpen = 1;
    sqlite3_vfs *pVfs = pWal->pVfs;
    if( pWal->hdr.iVersion==0 && pWal->bWal2==0 ){
      rc = sqlite3OsAccess(pVfs, pWal->zWalName2, SQLITE_ACCESS_EXISTS, &bOpen);
    }
    if( rc==SQLITE_OK && bOpen ){
................................................................................
      }else

      /* Fallback */
      if( nCkpt1<=nCkpt2 ){
        pWal->hdr = hdr;
      }else{
        walidxSetFile(&pWal->hdr, 1);
        walidxSetMxFrame(&pWal->hdr, 1, pWal->hdr.mxFrame);
        walidxSetMxFrame(&pWal->hdr, 0, 0);
      }
      pWal->hdr.iVersion = WAL_VERSION2;
    }else{
      pWal->hdr.iVersion = WAL_VERSION1;
    }

    walIndexWriteHdr(pWal);

Changes to test/wal2simple.test.

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    } [list ok $NROW $nTotal]

    db2 close
  }
}






























































finish_test







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    } [list ok $NROW $nTotal]

    db2 close
  }
}


#-------------------------------------------------------------------------
reset_db
do_execsql_test 6.0 {
  CREATE TABLE tx(x);
  PRAGMA journal_mode = wal2;
  PRAGMA journal_size_limit = 3500;
} {wal2 3500}

do_test 6.1 {
  for {set i 0} {$i < 10} {incr i} {
    execsql "CREATE TABLE t$i (x);"
  }
} {}

puts "[file size test.db-wal] [file size test.db-wal2]"

do_test 6.2.1 {
  foreach f [glob -nocomplain test.db2*] { forcedelete $f }
  forcecopy test.db-wal2 test.db2-wal2
  sqlite3 db2 test.db2
  db2 eval { SELECT * FROM sqlite_master }
} {}
do_test 6.2.2 {
  db2 eval {
    PRAGMA journal_mode = wal2;
    SELECT * FROM sqlite_master;
  }
} {wal2}

do_test 6.3.1 {
  db2 close
  foreach f [glob -nocomplain test.db2*] { forcedelete $f }
  forcecopy test.db-wal2 test.db2-wal2
  forcecopy test.db test.db2
  sqlite3 db2 test.db2
  db2 eval { SELECT * FROM sqlite_master }
} {table tx tx 2 {CREATE TABLE tx(x)}}
do_test 6.3.2 {
  db2 eval {
    PRAGMA journal_mode = wal2;
    SELECT * FROM sqlite_master;
  }
} {wal2 table tx tx 2 {CREATE TABLE tx(x)}}

do_test 6.4.1 {
  db2 close
  foreach f [glob -nocomplain test.db2*] { forcedelete $f }
  forcecopy test.db-wal2 test.db2-wal2
  forcecopy test.db-wal test.db2-wal
  sqlite3 db2 test.db2
  db2 eval { SELECT * FROM sqlite_master }
} {}
do_test 6.4.2 {
  db2 eval {
    PRAGMA journal_mode = wal2;
    SELECT * FROM sqlite_master;
  }
} {wal2}
db2 close

finish_test