private IntPtr[] CompressPages(Transaction tx, int numberOfPages, IVirtualPager compressionPager, uint previousTransactionCrc)
{
// numberOfPages include the tx header page, which we don't compress
var dataPagesCount = numberOfPages - 1;
var sizeInBytes = dataPagesCount * AbstractPager.PageSize;
var outputBuffer = LZ4.MaximumOutputLength(sizeInBytes);
var outputBufferInPages = outputBuffer / AbstractPager.PageSize +
(outputBuffer % AbstractPager.PageSize == 0 ? 0 : 1);
var pagesRequired = (dataPagesCount + outputBufferInPages);
compressionPager.EnsureContinuous(tx, 0, pagesRequired);
var tempBuffer = compressionPager.AcquirePagePointer(0);
var compressionBuffer = compressionPager.AcquirePagePointer(dataPagesCount);
var write = tempBuffer;
var txPages = tx.GetTransactionPages();
foreach (var txPage in txPages)
{
var scratchPage = tx.Environment.ScratchBufferPool.AcquirePagePointer(txPage.ScratchFileNumber, txPage.PositionInScratchBuffer);
var count = txPage.NumberOfPages * AbstractPager.PageSize;
MemoryUtils.BulkCopy(write, scratchPage, count);
write += count;
}
var len = DoCompression(tempBuffer, compressionBuffer, sizeInBytes, outputBuffer);
var remainder = len % AbstractPager.PageSize;
var compressedPages = (len / AbstractPager.PageSize) + (remainder == 0 ? 0 : 1);
if (remainder != 0)
{
// zero the remainder of the page
StdLib.memset(compressionBuffer + len, 0, remainder);
}
var pages = new IntPtr[compressedPages + 1];
var txHeaderPage = tx.GetTransactionHeaderPage();
var txHeaderBase = tx.Environment.ScratchBufferPool.AcquirePagePointer(txHeaderPage.ScratchFileNumber, txHeaderPage.PositionInScratchBuffer);
var txHeader = (TransactionHeader *)txHeaderBase;
txHeader->Compressed = true;
txHeader->CompressedSize = len;
txHeader->UncompressedSize = sizeInBytes;
txHeader->PreviousTransactionCrc = previousTransactionCrc;
pages[0] = new IntPtr(txHeaderBase);
for (int index = 0; index < compressedPages; index++)
{
pages[index + 1] = new IntPtr(compressionBuffer + (index * AbstractPager.PageSize));
}
txHeader->Crc = Crc.Value(compressionBuffer, 0, compressedPages * AbstractPager.PageSize);
return(pages);
}
public override int WriteDirect(Page start, long pagePosition, int pagesToWrite)
{
ThrowObjectDisposedIfNeeded();
int toCopy = pagesToWrite * PageSize;
MemoryUtils.BulkCopy(PagerState.MapBase + pagePosition * PageSize, start.Base, toCopy);
return(toCopy);
}