/*
*
* Layout: [ Doc Guid (16 bytes) | PageLink[0] (5 bytes) | PageLink[1] (5 bytes) ] --> 26 bytes
* We can fit 157 in a 4k page. Gives us 6 ranks (126 entries) -> 3276 bytes
* Our pages are currently 4061 bytes, so we have plenty of spare space if we can find useful metadata to store.
*
* We assume but don't store a root page with guid {127,127...,127}. The first two entries are 'left' and 'right' on the second level.
*
*/
public IndexPage()
{
_links = new VersionedLink[EntryCount];
for (int i = 0; i < EntryCount; i++)
{
_links[i] = new VersionedLink();
}
_docIds = new Guid[EntryCount];
}
[NotNull] private VersionedLink GetLink(int headOffset)
{
var result = new VersionedLink();
lock (_fslock)
{
_fs.Seek(MAGIC_SIZE + (VersionedLink.ByteSize * headOffset), SeekOrigin.Begin);
result.Defrost(_fs);
}
return(result);
}
private void SetLink(int headOffset, VersionedLink value)
{
if (value == null)
{
throw new Exception("Attempted to set invalid header link");
}
var strm = value.Freeze();
lock (_fslock)
{
_fs.Seek(MAGIC_SIZE + (VersionedLink.ByteSize * headOffset), SeekOrigin.Begin);
strm.CopyTo(_fs);
}
}
/// <summary>
/// Update a link to set an invalid link. Both versions of the link will be lost.
/// Returns true if a change was made. False if the link was not found in this index page
/// </summary>
/// <param name="docId">ID of document to update</param>
/// <returns></returns>
public bool Remove(Guid docId)
{
// find the entry to update
var index = Find(docId);
if (index < 0 || index >= EntryCount)
{
return(false); // not found
}
if (_docIds[index] == ZeroDocId)
{
return(false); // not found
}
if (_docIds[index] != docId)
{
throw new Exception("IndexPage.Remove: Logic error");
}
_links[index] = new VersionedLink(); // entirely reset
return(true);
}
public static void InitialiseDb([NotNull] Stream fs)
{
if (!fs.CanWrite)
{
throw new Exception("Tried to initialise a read-only stream");
}
fs.Seek(0, SeekOrigin.Begin);
foreach (var b in HEADER_MAGIC)
{
fs.WriteByte(b);
}
// write disabled links for the three core chains
var indexVersion = new VersionedLink();
var pathLookupVersion = new VersionedLink();
var freeListVersion = new VersionedLink();
indexVersion.Freeze().CopyTo(fs);
pathLookupVersion.Freeze().CopyTo(fs);
freeListVersion.Freeze().CopyTo(fs);
Flush(fs);
}
private void SetFreeListLink(VersionedLink value)
{
SetLink(2, value);
}
private void SetPathLookupLink(VersionedLink value)
{
SetLink(1, value);
}
private void SetIndexPageLink(VersionedLink value)
{
SetLink(0, value);
}
