Class CachedPage

java.lang.Object
org.apache.derby.impl.store.raw.data.BasePage
org.apache.derby.impl.store.raw.data.CachedPage
All Implemented Interfaces:
Cacheable, TypedFormat, DerbyObserver, Page
Direct Known Subclasses:
StoredPage
public abstract class CachedPage extends BasePage implements Cacheable
A base page that is cached. Since there are multiple page formats, use this abstract class to implement cacheable interface.

  • Field Details

    • alreadyReadPage

      protected boolean alreadyReadPage

    • pageData

      protected byte[] pageData

    • isDirty

      protected boolean isDirty

    • preDirty

      protected boolean preDirty

    • initialRowCount

      protected int initialRowCount

    • containerRowCount

      private long containerRowCount

    • pageCache

      protected CacheManager pageCache
      The page cache I live in.
      MT - Immutable

    • containerCache

      protected CacheManager containerCache
      The container cache my container lives in.
      MT - Immutable

    • dataFactory

      protected BaseDataFileFactory dataFactory
      My factory class.
      MT - Immutable -

    • PAGE_FORMAT_ID_SIZE

      protected static final int PAGE_FORMAT_ID_SIZE
      See Also:

    • WRITE_SYNC

      public static final int WRITE_SYNC
      See Also:

    • WRITE_NO_SYNC

      public static final int WRITE_NO_SYNC
      See Also:

  • Constructor Details

    • CachedPage

      public CachedPage()

  • Method Details

    • setFactory

      public final void setFactory(BaseDataFileFactory factory)

    • initialize

      protected void initialize()
      Initialize a CachedPage.

      Initialize the object, ie. perform work normally perfomed in constructor. Called by setIdentity() and createIdentity().

      Overrides:
      initialize in class BasePage

    • setIdentity

      public Cacheable setIdentity(Object key) throws StandardException
      Find the container and then read the page from that container.

      This is the way new pages enter the page cache.

      Specified by:
      setIdentity in interface Cacheable
      Returns:
      always true, higher levels have already checked the page number is valid for an open.
      Throws:
      StandardException - Standard Derby policy.
      See Also:

    • createIdentity

      public Cacheable createIdentity(Object key, Object createParameter) throws StandardException
      Find the container and then create the page in that container.

      This is the process of creating a new page in a container, in that case no need to read the page from disk - just need to initialize it in the cache.

      Specified by:
      createIdentity in interface Cacheable
      Parameters:
      key - Which page is this?
      createParameter - details needed to create page like size, format id, ...
      Returns:
      new page, higher levels have already checked the page number is valid for an open.
      Throws:
      StandardException - Standard exception policy.
      See Also:

    • changeInstanceTo

      private CachedPage changeInstanceTo(int fid, PageKey newIdentity) throws StandardException
      Convert this page to requested type, as defined by input format id.

      The current cache entry is a different format id than the requested type, change it. This object is instantiated to the wrong subtype of cachedPage, this routine will create an object with the correct subtype, and transfer all pertinent information from this to the new correct object.

      Parameters:
      fid - The format id of the new page.
      newIdentity - The key of the new page.
      Returns:
      The new object created with the input fid and transfered info.
      Throws:
      StandardException - Standard exception policy.

    • isDirty

      public boolean isDirty()
      Is the page dirty?

      The isDirty flag indicates if the pageData or pageHeader has been modified. The preDirty flag indicates that the pageData or the pageHeader is about to be modified. The reason for these 2 flags instead of just one is to accomodate checkpoint. After a clean (latched) page sends a log record to the log stream but before that page is dirtied by the log operation, a checkpoint could be taken. If so, then the redoLWM will be after the log record but, without preDirty, the cache cleaning will not have waited for the change. So the preDirty bit is to stop the cache cleaning from skipping over this (latched) page even though it has not really been modified yet.

      Specified by:
      isDirty in interface Cacheable
      Returns:
      true if the page is dirty.
      See Also:

    • isActuallyDirty

      public boolean isActuallyDirty()
      Has the page or its header been modified.

      See comment on class header on meaning of isDirty and preDirty bits.

      Returns:
      true if changes have actually been made to the page in memory.

    • preDirty

      public void preDirty()
      Set state to indicate the page or its header is about to be modified.

      See comment on class header on meaning of isDirty and preDirty bits.

      Specified by:
      preDirty in class BasePage

    • setDirty

      protected void setDirty()
      Set state to indicate the page or its header has been modified.

      See comment on class header on meaning of isDirty and preDirty bits.

    • releaseExclusive

      protected void releaseExclusive()
      exclusive latch on page is being released.

      The only work done in CachedPage is to update the row count on the container if it is too out of sync.

      Overrides:
      releaseExclusive in class BasePage

    • clean

      public void clean(boolean remove) throws StandardException
      Write the page to disk.

      MP - In a simple world we would just not allow clean until it held the latch on the page. But in order to fit into the cache system, we don't have enough state around to just make clean() latch the page while doing the I/O - but we still need someway to insure that no changes happen to the page while the I/O is taking place. Also someday it would be fine to allow reads of this page while the I/O was taking place.

      Specified by:
      clean in interface Cacheable
      Throws:
      StandardException - Error writing the page.
      See Also:

    • clearIdentity

      public void clearIdentity()
      Description copied from interface: Cacheable
      Put the object into the No Identity state.
      MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.
      Specified by:
      clearIdentity in interface Cacheable
      Overrides:
      clearIdentity in class BasePage

    • readPage

      private void readPage(FileContainer myContainer, PageKey newIdentity) throws StandardException
      read the page from disk into this CachedPage object.

      A page is read in from disk into the pageData array of this object, and then put in the cache.

      Parameters:
      myContainer - the container to read the page from.
      newIdentity - indentity (ie. page number) of the page to read
      Throws:
      StandardException - Standard exception policy.

    • writePage

      private void writePage(PageKey identity, boolean syncMe) throws StandardException
      write the page from this CachedPage object to disk.

      Parameters:
      identity - indentity (ie. page number) of the page to read
      syncMe - does the write of this single page have to be sync'd?
      Throws:
      StandardException - Standard exception policy.

    • setContainerRowCount

      public void setContainerRowCount(long rowCount)
      Description copied from class: BasePage
      Set the number of rows in the container - the page uses this to decide whether it needs to aggressive set the container's row count when it changes.
      Specified by:
      setContainerRowCount in class BasePage

    • setPageArray

      protected void setPageArray(int pageSize)
      if the page size is different from the page buffer, then make a new page buffer and make subclass use the new page buffer

    • getPageArray

      protected byte[] getPageArray() throws StandardException
      Returns the page data array used to write on disk version.

      returns the page data array, that is actually written to the disk, when the page is cleaned from the page cache. Takes care of flushing in-memory information to the array (like page header and format id info).

      Specified by:
      getPageArray in class BasePage
      Returns:
      The array of bytes that is the on disk version of page.
      Throws:
      StandardException - Standard exception policy.

    • usePageBuffer

      protected abstract void usePageBuffer(byte[] buffer)

    • initFromData

      protected abstract void initFromData(FileContainer container, PageKey id) throws StandardException
      Throws:
      StandardException

    • createPage

      protected abstract void createPage(PageKey id, PageCreationArgs args) throws StandardException
      Throws:
      StandardException

    • writePage

      protected abstract void writePage(PageKey id) throws StandardException
      Throws:
      StandardException

    • writeFormatId

      protected abstract void writeFormatId(PageKey identity) throws StandardException
      Throws:
      StandardException