/// <summary>
/// Scans a heap beginning from the provided IAM page and onwards.
/// </summary>
private IEnumerable <Row> scanHeap(PagePointer loc, Row schema, CompressionContext compression)
{
// Traverse the linked list of IAM pages untill the tail pointer is zero
while (loc != PagePointer.Zero)
{
// Before scanning, check that the IAM page itself is allocated
var pfsPage = Database.GetPfsPage(PfsPage.GetPfsPointerForPage(loc));
// If IAM page isn't allocated, there's nothing to return
if (!pfsPage.GetPageDescription(loc.PageID).IsAllocated)
{
yield break;
}
var iamPage = Database.GetIamPage(loc);
// Create an array with all of the header slot pointers
var iamPageSlots = new[]
{
iamPage.Slot0,
iamPage.Slot1,
iamPage.Slot2,
iamPage.Slot3,
iamPage.Slot4,
iamPage.Slot5,
iamPage.Slot6,
iamPage.Slot7
};
// Loop each header slot and yield the results, provided the header slot is allocated
foreach (var slot in iamPageSlots.Where(x => x != PagePointer.Zero))
{
var recordParser = RecordEntityParser.CreateEntityParserForPage(slot, compression, Database);
foreach (var dr in recordParser.GetEntities(schema))
{
yield return(dr);
}
}
// Then loop through allocated extents and yield results
foreach (var extent in iamPage.GetAllocatedExtents())
{
// Get PFS page that tracks this extent
var pfs = Database.GetPfsPage(PfsPage.GetPfsPointerForPage(extent.StartPage));
foreach (var pageLoc in extent.GetPagePointers())
{
// Check if page is allocated according to PFS page
var pfsDescription = pfs.GetPageDescription(pageLoc.PageID);
if (!pfsDescription.IsAllocated)
{
continue;
}
var recordParser = RecordEntityParser.CreateEntityParserForPage(pageLoc, compression, Database);
foreach (var dr in recordParser.GetEntities(schema))
{
yield return(dr);
}
}
}
// Update current IAM chain location to the tail pointer
loc = iamPage.Header.NextPage;
}
}
