public RC Step(int pages)
{
MutexEx.Enter(SrcCtx.Mutex);
Src.Enter();
if (DestCtx != null)
MutexEx.Enter(DestCtx.Mutex);
RC rc = RC_;
if (!IsFatalError(rc))
{
Pager srcPager = Src.get_Pager(); // Source pager
Pager destPager = Dest.get_Pager(); // Dest pager
Pid srcPage = 0; // Size of source db in pages
bool closeTrans = false; // True if src db requires unlocking
// If the source pager is currently in a write-transaction, return SQLITE_BUSY immediately.
rc = (DestCtx != null && Src.Bt.InTransaction == TRANS.WRITE ? RC.BUSY : RC.OK);
// Lock the destination database, if it is not locked already.
if (rc == RC.OK && !DestLocked && (rc = Dest.BeginTrans(2)) == RC.OK)
{
DestLocked = true;
Dest.GetMeta(Btree.META.SCHEMA_VERSION, ref DestSchema);
}
// If there is no open read-transaction on the source database, open one now. If a transaction is opened here, then it will be closed
// before this function exits.
if (rc == RC.OK && !Src.IsInReadTrans())
{
rc = Src.BeginTrans(0);
closeTrans = true;
}
// Do not allow backup if the destination database is in WAL mode and the page sizes are different between source and destination
int pgszSrc = Src.GetPageSize(); // Source page size
int pgszDest = Dest.GetPageSize(); // Destination page size
IPager.JOURNALMODE destMode = Dest.get_Pager().GetJournalMode(); // Destination journal mode
if (rc == RC.OK && destMode == IPager.JOURNALMODE.WAL && pgszSrc != pgszDest)
rc = RC.READONLY;
// Now that there is a read-lock on the source database, query the source pager for the number of pages in the database.
srcPage = Src.LastPage();
Debug.Assert(srcPage >= 0);
for (int ii = 0; (pages < 0 || ii < pages) && NextId <= (Pid)srcPage && rc == 0; ii++)
{
Pid srcPg = NextId; // Source page number
if (srcPg != Btree.PENDING_BYTE_PAGE(Src.Bt))
{
IPage srcPgAsObj = null; // Source page object
rc = srcPager.Acquire(srcPg, ref srcPgAsObj, false);
if (rc == RC.OK)
{
rc = BackupOnePage(p, srcPg, Pager.GetData(srcPgAsObj), false);
Pager.Unref(srcPgAsObj);
}
}
NextId++;
}
if (rc == RC.OK)
{
Pagecount = srcPage;
Remaining = (srcPage + 1 - NextId);
if (NextId > srcPage)
rc = RC.DONE;
else if (!IsAttached)
AttachBackupObject(p);
}
// Update the schema version field in the destination database. This is to make sure that the schema-version really does change in
// the case where the source and destination databases have the same schema version.
if (rc == RC.DONE)
{
if (srcPage == null)
{
rc = Dest.NewDb();
srcPage = 1;
}
if (rc == RC.OK || rc == RC.DONE)
rc = Dest.UpdateMeta(Btree.META.SCHEMA_VERSION, DestSchema + 1);
if (rc == RC.OK)
{
if (DestCtx != null)
Main.ResetAllSchemasOfConnection(DestCtx);
if (destMode == IPager.JOURNALMODE.WAL)
rc = Dest.SetVersion(2);
}
if (rc == RC.OK)
{
// Set nDestTruncate to the final number of pages in the destination database. The complication here is that the destination page
// size may be different to the source page size.
//
// If the source page size is smaller than the destination page size, round up. In this case the call to sqlite3OsTruncate() below will
// fix the size of the file. However it is important to call sqlite3PagerTruncateImage() here so that any pages in the
// destination file that lie beyond the nDestTruncate page mark are journalled by PagerCommitPhaseOne() before they are destroyed
// by the file truncation.
Debug.Assert(pgszSrc == Src.GetPageSize());
Debug.Assert(pgszDest == Dest.GetPageSize());
Pid destTruncate;
if (pgszSrc < pgszDest)
{
int ratio = pgszDest / pgszSrc;
destTruncate = (Pid)((srcPage + ratio - 1) / ratio);
if (destTruncate == Btree.PENDING_BYTE_PAGE(Dest.Bt))
destTruncate--;
}
else
destTruncate = (Pid)(srcPage * (pgszSrc / pgszDest));
Debug.Assert(destTruncate > 0);
if (pgszSrc < pgszDest)
{
// If the source page-size is smaller than the destination page-size, two extra things may need to happen:
//
// * The destination may need to be truncated, and
//
// * Data stored on the pages immediately following the pending-byte page in the source database may need to be
// copied into the destination database.
int size = (int)(pgszSrc * srcPage);
VFile file = destPager.get_File();
Debug.Assert(file != null);
Debug.Assert((long)destTruncate * (long)pgszDest >= size || (destTruncate == (int)(Btree.PENDING_BYTE_PAGE(Dest.Bt) - 1) && size >= VFile.PENDING_BYTE && size <= VFile.PENDING_BYTE + pgszDest));
// This block ensures that all data required to recreate the original database has been stored in the journal for pDestPager and the
// journal synced to disk. So at this point we may safely modify the database file in any way, knowing that if a power failure
// occurs, the original database will be reconstructed from the journal file.
uint dstPage;
destPager.Pages(out dstPage);
for (Pid pg = destTruncate; rc == RC.OK && pg <= (Pid)dstPage; pg++)
{
if (pg != Btree.PENDING_BYTE_PAGE(Dest.Bt))
{
IPage pgAsObj;
rc = destPager.Acquire(pg, ref pgAsObj, false);
if (rc == RC.OK)
{
rc = Pager.Write(pgAsObj);
Pager.Unref(pgAsObj);
}
}
}
if (rc == RC.OK)
rc = destPager.CommitPhaseOne(null, true);
// Write the extra pages and truncate the database file as required.
long end = Math.Min(VFile.PENDING_BYTE + pgszDest, size);
for (long off = VFile.PENDING_BYTE + pgszSrc; rc == RC.OK && off < end; off += pgszSrc)
{
Pid srcPg = (Pid)((off / pgszSrc) + 1);
PgHdr srcPgAsObj = null;
rc = srcPager.Acquire(srcPg, ref srcPgAsObj, false);
if (rc == RC.OK)
{
byte[] data = Pager.GetData(srcPgAsObj);
rc = file.Write(data, pgszSrc, off);
}
Pager.Unref(srcPgAsObj);
}
if (rc == RC.OK)
rc = BackupTruncateFile(file, (int)size);
// Sync the database file to disk.
if (rc == RC.OK)
rc = destPager.Sync();
}
else
{
destPager.TruncateImage(destTruncate);
rc = destPager.CommitPhaseOne(null, false);
}
// Finish committing the transaction to the destination database.
if (rc == RC.OK && (rc = Dest.CommitPhaseTwo(false)) == RC.OK)
rc = RC.DONE;
}
}
// If bCloseTrans is true, then this function opened a read transaction on the source database. Close the read transaction here. There is
// no need to check the return values of the btree methods here, as "committing" a read-only transaction cannot fail.
if (closeTrans)
{
#if !DEBUG || COVERAGE_TEST
RC rc2 = Src.CommitPhaseOne(null);
rc2 |= Src.CommitPhaseTwo(false);
Debug.Assert(rc2 == RC.OK);
#else
Src.CommitPhaseOne(null);
Src.CommitPhaseTwo(false);
#endif
}
if (rc == RC.IOERR_NOMEM)
rc = RC.NOMEM;
RC_ = rc;
}
if (DestCtx != null)
MutexEx.Leave(DestCtx.Mutex);
Src.Leave();
MutexEx.Leave(SrcCtx.Mutex);
return rc;
}
static RC BackupOnePage(Backup p, Pid srcPg, byte[] srcData, bool update)
{
Pager destPager = p.Dest.get_Pager();
int srcPgsz = p.Src.GetPageSize();
int destPgsz = p.Dest.GetPageSize();
int copy = Math.Min(srcPgsz, destPgsz);
long end = (long)srcPg * (long)srcPgsz;
RC rc = RC.OK;
Debug.Assert(p.Src.GetReserveNoMutex() >= 0);
Debug.Assert(p.DestLocked);
Debug.Assert(!IsFatalError(p.RC_));
Debug.Assert(srcPg != Btree.PENDING_BYTE_PAGE(p.Src.Bt));
Debug.Assert(srcData != null);
// Catch the case where the destination is an in-memory database and the page sizes of the source and destination differ.
if (srcPgsz != destPgsz && destPager.get_MemoryDB)
rc = RC.READONLY;
#if HAS_CODEC
int srcReserve = p.Src.GetReserveNoMutex();
int destReserve = p.Dest.GetReserve();
// Backup is not possible if the page size of the destination is changing and a codec is in use.
if (srcPgsz != destPgsz && Pager.GetCodec(destPager) != null)
rc = RC.READONLY;
// Backup is not possible if the number of bytes of reserve space differ between source and destination. If there is a difference, try to
// fix the destination to agree with the source. If that is not possible, then the backup cannot proceed.
if (srcReserve != destReserve)
{
uint newPgsz = (uint)srcPgsz;
rc = destPager.SetPageSize(ref newPgsz, srcReserve);
if (rc == RC.OK && newPgsz != srcPgsz)
rc = RC.READONLY;
}
#endif
// This loop runs once for each destination page spanned by the source page. For each iteration, variable iOff is set to the byte offset
// of the destination page.
for (long off = end - (long)srcPgsz; rc == RC.OK && off < end; off += destPgsz)
{
IPage destPg = null;
uint dest = (uint)(off / destPgsz) + 1;
if (dest == Btree.PENDING_BYTE_PAGE(p.Dest.Bt))
continue;
if ((rc = destPager.Acquire(dest, ref destPg, false)) == RC.OK && (rc = Pager.Write(destPg)) == RC.OK)
{
byte[] destData = Pager.GetData(destPg);
// Copy the data from the source page into the destination page. Then clear the Btree layer MemPage.isInit flag. Both this module
// and the pager code use this trick (clearing the first byte of the page 'extra' space to invalidate the Btree layers
// cached parse of the page). MemPage.isInit is marked "MUST BE FIRST" for this purpose.
Buffer.BlockCopy(srcData, (int)(off % srcPgsz), destData, (int)(off % destPgsz), copy);
Pager.GetExtra(destPg).IsInit = false;
}
Pager.Unref(destPg);
}
return rc;
}