SQLite

  int rc;
  PgHdr *pPg;                   /* An existing page in the cache */
  Pgno pgno;                    /* The page number of a page in journal */
  u32 cksum;                    /* Checksum used for sanity checking */
  char *aData;                  /* Temporary storage for the page */
  sqlite3_file *jfd;            /* The file descriptor for the journal file */
  int isSynced;                 /* True if journal page is synced */
  const int jrnlEnc = (isMainJrnl || pPager->subjInMemory==0);

  assert( (isMainJrnl&~1)==0 );      /* isMainJrnl is 0 or 1 */
  assert( (isSavepnt&~1)==0 );       /* isSavepnt is 0 or 1 */
  assert( isMainJrnl || pDone );     /* pDone always used on sub-journals */
  assert( isSavepnt || pDone==0 );   /* pDone never used on non-savepoint */

  aData = pPager->pTmpSpace;

  if( isOpen(pPager->fd)
   && (pPager->eState>=PAGER_WRITER_DBMOD || pPager->eState==PAGER_OPEN)
   && isSynced
  ){
    i64 ofst = (pgno-1)*(i64)pPager->pageSize;
    testcase( !isSavepnt && pPg!=0 && (pPg->flags&PGHDR_NEED_SYNC)!=0 );
    assert( !pagerUseWal(pPager) );

    /* Write the data read from the journal back into the database file.
    ** This is usually safe even for an encrypted database - as the data
    ** was encrypted before it was written to the journal file. The exception
    ** is if the data was just read from an in-memory sub-journal. In that
    ** case it must be encrypted here before it is copied into the database
    ** file.  */
    if( !jrnlEnc ){CODEC2(pPager, aData, pgno, 7, rc=SQLITE_NOMEM_BKPT, aData);}
    rc = sqlite3OsWrite(pPager->fd, (u8 *)aData, pPager->pageSize, ofst);
    if( !jrnlEnc ){CODEC1(pPager, aData, pgno, 3, rc=SQLITE_NOMEM_BKPT);}

    if( pgno>pPager->dbFileSize ){
      pPager->dbFileSize = pgno;
    }
    if( pPager->pBackup ){
      if( jrnlEnc ){CODEC1(pPager, aData, pgno, 3, rc=SQLITE_NOMEM_BKPT);}
      sqlite3BackupUpdate(pPager->pBackup, pgno, (u8*)aData);
      if( jrnlEnc ){CODEC2(pPager, aData, pgno, 7, rc=SQLITE_NOMEM_BKPT,aData);}
    }
  }else if( !isMainJrnl && pPg==0 ){
    /* If this is a rollback of a savepoint and data was not written to
    ** the database and the page is not in-memory, there is a potential
    ** problem. When the page is next fetched by the b-tree layer, it 
    ** will be read from the database file, which may or may not be 
    ** current. 

    /* If this was page 1, then restore the value of Pager.dbFileVers.
    ** Do this before any decoding. */
    if( pgno==1 ){
      memcpy(&pPager->dbFileVers, &((u8*)pData)[24],sizeof(pPager->dbFileVers));
    }

    /* Decode the page just read from disk */
    if( jrnlEnc ) CODEC1(pPager, pData, pPg->pgno, 3, rc=SQLITE_NOMEM_BKPT);
    sqlite3PcacheRelease(pPg);
  }
  return rc;
}

/*
** Parameter zMaster is the name of a master journal file. A single journal

    /* If the sub-journal was opened successfully (or was already open),
    ** write the journal record into the file.  */
    if( rc==SQLITE_OK ){
      void *pData = pPg->pData;
      i64 offset = (i64)pPager->nSubRec*(4+pPager->pageSize);
      char *pData2;
  
      if( pPager->subjInMemory ){
        pData2 = pData;
      }else{
        CODEC2(pPager, pData, pPg->pgno, 7, return SQLITE_NOMEM_BKPT, pData2);
      }
      PAGERTRACE(("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg->pgno));
      rc = write32bits(pPager->sjfd, offset, pPg->pgno);
      if( rc==SQLITE_OK ){
        rc = sqlite3OsWrite(pPager->sjfd, pData2, pPager->pageSize, offset+4);
      }
    }
  }

# 2017 May 9
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix subjournal

do_execsql_test 1.0 {
  PRAGMA temp_store = memory;
  CREATE TABLE t1(a,b,c);
  INSERT INTO t1 VALUES(1, 2, 3);
} {}
do_execsql_test 1.1 {
  BEGIN;
    INSERT INTO t1 VALUES(4, 5, 6);
    SAVEPOINT one;
      INSERT INTO t1 VALUES(7, 8, 9);
    ROLLBACK TO one;
    SELECT * FROM t1;
} {1 2 3 4 5 6}
do_execsql_test 1.2 {
  COMMIT;
}

do_execsql_test 2.0 {
  PRAGMA cache_size = 5;
  CREATE TABLE t2(a BLOB);
  CREATE INDEX i2 ON t2(a);
  WITH s(i) AS (
    SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<100
  ) INSERT INTO t2 SELECT randomblob(500) FROM s;
}

do_test 2.1 {
  forcedelete test.db2
  sqlite3 db2 test2.db
  sqlite3_backup B db2 main db main
  set nPage [db one {PRAGMA page_count}]
  B step [expr $nPage-10]
} {SQLITE_OK}

do_execsql_test 2.2 {
  BEGIN;
    UPDATE t2 SET a=randomblob(499);
    SAVEPOINT two;
      UPDATE t2 SET a=randomblob(498);
    ROLLBACK TO two;
  COMMIT;
  PRAGMA integrity_check;
} {ok}

do_test 2.3 {
  B step 1000
} {SQLITE_DONE}
do_test 2.4 {
  B finish
  execsql { PRAGMA integrity_check } db2
} {ok}

finish_test