/// <summary>
/// Get a page from cache or from disk (get from cache or from disk)
/// </summary>
public T GetPage <T>(uint pageID)
where T : BasePage
{
lock (_disk)
{
var page = _cache.GetPage(pageID);
// is not on cache? load from disk
if (page == null)
{
var buffer = _disk.ReadPage(pageID);
// if datafile are encrypted, decrypt buffer (header are not encrypted)
if (_crypto != null && pageID > 0)
{
buffer = _crypto.Decrypt(buffer);
}
page = BasePage.ReadPage(buffer);
_cache.AddPage(page);
}
return((T)page);
}
}
private void AvoidDirtyRead()
{
// if disk are exclusive don't need check dirty read
if (_disk.IsExclusive)
{
return;
}
_log.Write(Logger.CACHE, "checking disk to avoid dirty read");
// empty cache? just exit
if (_cache.CleanUsed == 0)
{
return;
}
// get ChangeID from cache
var header = _cache.GetPage(0) as HeaderPage;
var changeID = header == null ? 0 : header.ChangeID;
// and get header from disk
var disk = BasePage.ReadPage(_disk.ReadPage(0)) as HeaderPage;
// if header change, clear cache and add new header to cache
if (disk.ChangeID != changeID)
{
_log.Write(Logger.CACHE, "file changed from another process, cleaning all cache pages");
_cache.ClearPages();
_cache.AddPage(disk);
}
}
/// <summary>
/// Get a page from cache or from disk (and put on cache)
/// </summary>
public T GetPage <T>(uint pageID, bool setDirty = false)
where T : BasePage
{
var page = _cache.GetPage(pageID);
// is not on cache? load from disk
if (page == null)
{
var buffer = _disk.ReadPage(pageID);
page = BasePage.ReadPage(buffer);
_cache.AddPage(page);
}
#if DEBUG
// if page is empty, convert to T
if (page.PageType == PageType.Empty && typeof(T) != typeof(BasePage))
{
throw new Exception("Pager.GetPage<T>() never shuld happend");
}
#endif
// set page as dirty if passing by param
if (setDirty)
{
this.SetDirty((T)page);
}
return((T)page);
}
/// <summary>
/// Get a page from cache or from disk (and put on cache)
/// </summary>
public T GetPage <T>(uint pageID)
where T : BasePage, new()
{
var page = _cache.GetPage <T>(pageID);
if (page == null)
{
page = _disk.ReadPage <T>(pageID);
_cache.AddPage(page);
}
return(page);
}
/// <summary>
/// Test if cache still valid (if datafile was changed by another process reset cache)
/// Returns true if file was changed
/// [Thread Safe]
/// </summary>
private bool DetectDatabaseChanges()
{
// if disk are exclusive don't need check dirty read
if (_disk.IsExclusive)
{
return(false);
}
// empty cache? just exit
if (_cache.CleanUsed == 0)
{
return(false);
}
_log.Write(Logger.CACHE, "checking disk to detect database changes from another process");
// get ChangeID from cache
var header = _cache.GetPage(0) as HeaderPage;
var changeID = header == null ? 0 : header.ChangeID;
// and get header from disk
var disk = BasePage.ReadPage(_disk.ReadPage(0)) as HeaderPage;
// if disk header are in recovery mode, throw exception to datafile re-open and recovery pages
if (disk.Recovery)
{
_log.Write(Logger.ERROR, "datafile in recovery mode, need re-open database");
throw LiteException.NeedRecover();
}
// if header change, clear cache and add new header to cache
if (disk.ChangeID != changeID)
{
_log.Write(Logger.CACHE, "file changed from another process, cleaning all cache pages");
_cache.ClearPages();
_cache.AddPage(disk);
return(true);
}
return(false);
}
/// <summary>
/// This method must be called before read/write operation to avoid dirty reads.
/// It's occurs when my cache contains pages that was changed in another process
/// </summary>
public bool AvoidDirtyRead()
{
var cache = (HeaderPage)_cache.GetPage(0);
if (cache == null)
{
return(false);
}
// read change direct from disk
var change = _disk.GetChangeID();
// if changeID was changed, file was changed by another process - clear all cache
if (cache.ChangeID != change)
{
_cache.Clear();
return(true);
}
return(false);
}
/// <summary>
/// Save all dirty pages to disk
/// </summary>
public void PersistDirtyPages()
{
// get header page
var header = _pager.GetPage <HeaderPage>(0);
// increase file changeID (back to 0 when overflow)
header.ChangeID = header.ChangeID == ushort.MaxValue ? (ushort)0 : (ushort)(header.ChangeID + (ushort)1);
// mark header as dirty
_pager.SetDirty(header);
_log.Write(Logger.DISK, "begin disk operations - changeID: {0}", header.ChangeID);
// write journal file in desc order to header be last page in disk
if (_disk.IsJournalEnabled)
{
_disk.WriteJournal(_cache.GetDirtyPages()
.OrderByDescending(x => x.PageID)
.Select(x => x.DiskData)
.Where(x => x.Length > 0)
.ToList(), header.LastPageID);
// mark header as recovery before start writing (in journal, must keep recovery = false)
header.Recovery = true;
// flush to disk to ensure journal is committed to disk before proceeding
_disk.Flush();
}
else
{
// if no journal extend, resize file here to fast writes
_disk.SetLength(BasePage.GetSizeOfPages(header.LastPageID + 1));
}
// write header page first. if header.Recovery == true, this ensures it's written to disk *before* we start changing pages
var headerPage = _cache.GetPage(0);
var headerBuffer = headerPage.WritePage();
_disk.WritePage(0, headerBuffer);
_disk.Flush();
// get all dirty page stating from Header page (SortedList)
// header page (id=0) always must be first page to write on disk because it's will mark disk as "in recovery"
foreach (var page in _cache.GetDirtyPages())
{
// we've already written the header, so skip it
if (page.PageID == 0)
{
continue;
}
// page.WritePage() updated DiskData with new rendered buffer
var buffer = _crypto == null || page.PageID == 0 ?
page.WritePage() :
_crypto.Encrypt(page.WritePage());
_disk.WritePage(page.PageID, buffer);
}
if (_disk.IsJournalEnabled)
{
// ensure changed pages are persisted to disk *before* we change header.Recovery to false
_disk.Flush();
// re-write header page but now with recovery=false
header.Recovery = false;
_log.Write(Logger.DISK, "re-write header page now with recovery = false");
_disk.WritePage(0, header.WritePage());
}
// mark all dirty pages as clean pages (all are persisted in disk and are valid pages)
_cache.MarkDirtyAsClean();
// flush all data direct to disk
_disk.Flush();
// discard journal file
_disk.ClearJournal(header.LastPageID);
}
