Class AllocPage

All Implemented Interfaces:
Cacheable, TypedFormat, DerbyObserver, Page

public class AllocPage extends StoredPage
An allocation page of the file container.

This class extends a normal Stored page, with the exception that a hunk of space may be 'borrowed' by the file container to store the file header.

The borrowed space is not visible to the alloc page even though it is present in the page data array. It is accessed directly by the FileContainer. Any change made to the borrowed space is not managed or seen by the allocation page.

The reason for having this borrowed space is so that the container header does not need to have a page of its own.

Page Format
An allocation page extends a stored page, the on disk format is different from a stored page in that N bytes are 'borrowed' by the container and the page header of an allocation page will be slightly bigger than a normal stored page. This N bytes are stored between the page header and the record space.

The reason why this N bytes can't simply be a row is because it needs to be statically accessible by the container object to avoid a chicken and egg problem of the container object needing to instantiate an alloc page object before it can be objectified, and an alloc page object needing to instantiate a container object before it can be objectified. So this N bytes must be stored outside of the normal record interface yet it must be settable because only the first alloc page has this borrowed space. Other (non-first) alloc page have N == 0.

                             [ borrowed ]
        +----------+-------------+---+---------+-------------------+-------------+--------+
        | FormatId | page header | N | N bytes | alloc extend rows | slot offset |checksum|
        +----------+-------------+---+---------+-------------------+-------------+--------+
        
N is a byte that indicates the size of the borrowed space. Once an alloc page is initialized, the value of N cannot change.

The maximum space that can be borrowed by the container is 256 bytes.

The allocation page are of the same page size as any other pages in the container. The first allocation page of the FileContainer starts at the first physical byte of the container. Subsequent allocation pages are chained via the nextAllocPageOffset. Each allocation page is expected to manage at least 1000 user pages (for 1K page size) so this chaining may not be a severe performance hit. The logical -> physical mapping of an allocation page is stored in the previous allocation page. The container object will need to maintain this mapping.

The following fields are stored in the page header

See Also:
  • Field Details

    • FORMAT_NUMBER

      public static final int FORMAT_NUMBER
      See Also:
    • nextAllocPageNumber

      private long nextAllocPageNumber
      alloc page header
    • nextAllocPageOffset

      private long nextAllocPageOffset
    • reserved1

      private long reserved1
    • reserved2

      private long reserved2
    • reserved3

      private long reserved3
    • reserved4

      private long reserved4
    • extent

      private AllocExtent extent
    • borrowedSpace

      private int borrowedSpace
    • ALLOC_PAGE_HEADER_OFFSET

      protected static final int ALLOC_PAGE_HEADER_OFFSET
      constants
      See Also:
    • ALLOC_PAGE_HEADER_SIZE

      protected static final int ALLOC_PAGE_HEADER_SIZE
      See Also:
    • BORROWED_SPACE_OFFSET

      protected static final int BORROWED_SPACE_OFFSET
      See Also:
    • BORROWED_SPACE_LEN

      protected static final int BORROWED_SPACE_LEN
      See Also:
    • MAX_BORROWED_SPACE

      protected static final int MAX_BORROWED_SPACE
      See Also:
    • TEST_MULTIPLE_ALLOC_PAGE

      public static final String TEST_MULTIPLE_ALLOC_PAGE
      Extent Testing Use these strings to simulate error conditions for testing purposes.
  • Constructor Details

    • AllocPage

      public AllocPage()
  • Method Details

    • getTypeFormatId

      public int getTypeFormatId()
      Return my format identifier.
      Specified by:
      getTypeFormatId in interface TypedFormat
      Overrides:
      getTypeFormatId in class StoredPage
      Returns:
      The identifier. (A UUID stuffed in an array of 16 bytes).
    • getMaxFreeSpace

      protected int getMaxFreeSpace()
      Description copied from class: StoredPage
      The maximum free space on this page possible.

      The the maximum amount of space that can be used on the page for the records and the slot offset table. NOTE: subclass may have overwitten it to report less freeSpace

      Overrides:
      getMaxFreeSpace in class StoredPage
      Returns:
      the maximum free space on this page possible.
    • createPage

      protected void createPage(PageKey newIdentity, PageCreationArgs args) throws StandardException
      Create a new alloc page.
      Overrides:
      createPage in class StoredPage
      Parameters:
      newIdentity - The key describing page (segment,container,page).
      args - information stored about the page, once in the container header and passed in through the object.
      Throws:
      StandardException - Standard exception policy.
    • createExtent

      private AllocExtent createExtent(long pageNum, int pageSize, int pagesAlloced, int availspace)
    • initFromData

      protected void initFromData(FileContainer myContainer, PageKey newIdentity) throws StandardException
      Initialize in memory structure using the buffer in pageData
      Overrides:
      initFromData in class StoredPage
      Parameters:
      myContainer - The container to read the page in from.
      newIdentity - The key representing page being read in (segment, container, page number)
      Throws:
      StandardException - If the page cannot be read correctly, or is inconsistent.
    • writePage

      protected void writePage(PageKey identity) throws StandardException
      Write the page out
      Overrides:
      writePage in class StoredPage
      Parameters:
      identity - The key of this page.
      Throws:
      StandardException - If the page cannot be written
    • readAllocPageHeader

      private void readAllocPageHeader() throws IOException
      Throws:
      IOException
    • updateAllocPageHeader

      private void updateAllocPageHeader() throws IOException
      Throws:
      IOException
    • readExtent

      private AllocExtent readExtent(int offset) throws IOException, ClassNotFoundException
      Throws:
      IOException
      ClassNotFoundException
    • writeExtent

      private void writeExtent(int offset) throws IOException
      Throws:
      IOException
    • WriteContainerInfo

      public static void WriteContainerInfo(byte[] containerInfo, byte[] epage, boolean create) throws StandardException
      Write the container information into the container information area.
      Parameters:
      containerInfo - the container information
      epage - the allocation page data which may not be fully formed, but is guarenteed to be big enough to cover the area inhibited by the container info
      create - if create, write out the length of the container info also. Else check to make sure epage's original container info is of the same length
      Throws:
      StandardException - standard Derby error policy
    • ReadContainerInfo

      public static void ReadContainerInfo(byte[] containerInfo, byte[] epage) throws StandardException
      Extract the container information from epage.
      Parameters:
      containerInfo - where to put the extracted information
      epage - the allocation page which has the container information. Epage may not be fully formed, but is guarenteed to be big enough to cover the area inhibited by the container info
      Throws:
      StandardException
    • nextFreePageNumber

      public long nextFreePageNumber(long pnum)
      Return the next free page number after given page number
    • addPage

      public void addPage(FileContainer mycontainer, long newPageNumber, RawTransaction ntt, BaseContainerHandle userHandle) throws StandardException
      Add a page which is managed by this alloc page. Return the page number of the newly added page.
      MT - thread aware (latched)
      Parameters:
      mycontainer - (future) allows the alloc page to call back to the container to grow the container by creating and syncing multiple pages at once
      ntt - the nested top action that is the allocation transaction. NTT will comit before the user transaction
      userHandle - the container handle that is opened by the user transaction. Use the userHandle to latch the new page so that it may remain latched after NTT is committed so the user transaction can guarentee to have an empty page
      Throws:
      StandardException - If the page cannot be added
    • deallocatePage

      public void deallocatePage(BaseContainerHandle userHandle, long pageNumber) throws StandardException
      Throws:
      StandardException
    • updateUnfilledPageInfo

      protected void updateUnfilledPageInfo(AllocExtent inputExtent)
    • canAddFreePage

      public boolean canAddFreePage(long lastAllocatedPage)
    • getNextAllocPageOffset

      public long getNextAllocPageOffset()
    • chainNewAllocPage

      public void chainNewAllocPage(BaseContainerHandle allocHandle, long newAllocPageNum, long newAllocPageOffset) throws StandardException
      Throws:
      StandardException
    • getNextAllocPageNumber

      public long getNextAllocPageNumber()
    • isLast

      public boolean isLast()
    • getLastPagenum

      public long getLastPagenum()
    • getMaxPagenum

      public long getMaxPagenum()
    • getLastPreallocPagenum

      protected long getLastPreallocPagenum()
    • getPageStatus

      protected int getPageStatus(long pageNumber)
    • setPageStatus

      protected void setPageStatus(LogInstant instant, long pageNumber, int newStatus) throws StandardException
      Do the actual page allocation/deallocation/ree underneath a log operation. Change the page status to new status
      Throws:
      StandardException - If the page cannot be allocated
    • chainNextAllocPage

      protected void chainNextAllocPage(LogInstant instant, long newAllocPageNum, long newAllocPageOffset) throws StandardException
      Chain the next page number and offset underneath a log record
      Throws:
      StandardException - Standard Derby error policy
    • compressSpace

      protected void compressSpace(LogInstant instant, int new_highest_page, int num_pages_truncated) throws StandardException
      Compress free pages.

      Compress the free pages at the end of the range maintained by this allocation page. All pages being compressed should be FREE. Only pages in the last allocation page can be compressed.

      Parameters:
      instant - log address for this operation.
      new_highest_page - The new highest page on this allocation page. The number is the offset of the page in the array of pages maintained by this allocation page, for instance a value of 0 indicates all page except the first one are to be truncated. If all pages are truncated then the offset is set to -1.
      num_pages_truncated - The number of allocated pages in this allocation page prior to the truncate. Note that all pages from NewHighestPage+1 through newHighestPage+num_pages_truncated should be FREE.
      Throws:
      StandardException - Standard exception policy.
    • undoCompressSpace

      protected void undoCompressSpace(LogInstant instant, int new_highest_page, int num_pages_truncated) throws StandardException
      Handle undo of compress space operation.
      Throws:
      StandardException
    • toString

      public String toString()
      Description copied from class: StoredPage
      debugging, print this page
      Overrides:
      toString in class StoredPage
    • getAllocExtent

      protected AllocExtent getAllocExtent()
      Return a copy of the allocExtent to be cached by the container. the container must take care to maintain its coherency by invalidating the cache before any update.
    • preAllocatePage

      protected void preAllocatePage(FileContainer myContainer, int preAllocThreshold, int preAllocSize)
      Preallocate user page if needed.
      Parameters:
      myContainer - the container object
      preAllocThreshold - start preallocating after this threshold
      preAllocSize - preallocate this number of pages
    • compress

      protected boolean compress(RawTransaction ntt, FileContainer myContainer) throws StandardException
      compress out empty pages at end of container.

      Call the extent to update the data structure make the bit map look like contiguous free pages at the end of the extent no longer exist. Similar to preallocate do the operation unlogged, need to force the change to the extent before actually removing the space from the file.

      The sequence is: 1) update extent data structure 2) force extent changes to disk 3) truncate pages If the system crashes between 1 and 2 then no changes are on disk. If the system crashes between 2 and 3 then there are extra pages in the file that extent does not know about, this is the same case as preallocation which the code already handes. It will handle any set of pages from 0 to all of the intended pages being truncated. The next allocate looks at actual size of file as does the right thing.

      MT - expect Container level X lock

      Throws:
      StandardException - Standard exception policy.