java.lang.Object
- org.apache.derby.impl.store.raw.data.BasePage
- - org.apache.derby.impl.store.raw.data.CachedPage
  - - org.apache.derby.impl.store.raw.data.StoredPage
    - - org.apache.derby.impl.store.raw.data.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:

AllocExtent

Field Summary

Fields
Modifier and Type	Field	Description
`protected static int`	`ALLOC_PAGE_HEADER_OFFSET`	constants
`protected static int`	`ALLOC_PAGE_HEADER_SIZE`
`protected static int`	`BORROWED_SPACE_LEN`
`protected static int`	`BORROWED_SPACE_OFFSET`
`private int`	`borrowedSpace`
`private AllocExtent`	`extent`
`static int`	`FORMAT_NUMBER`
`protected static int`	`MAX_BORROWED_SPACE`
`private long`	`nextAllocPageNumber`	alloc page header
`private long`	`nextAllocPageOffset`
`private long`	`reserved1`
`private long`	`reserved2`
`private long`	`reserved3`
`private long`	`reserved4`
`static java.lang.String`	`TEST_MULTIPLE_ALLOC_PAGE`	Extent Testing Use these strings to simulate error conditions for testing purposes.

Fields inherited from class org.apache.derby.impl.store.raw.data.StoredPage
bh, CHECKSUM_SIZE, COLUMN_CREATE_NULL, COLUMN_FIRST, COLUMN_LONG, COLUMN_NONE, freeSpace, LARGE_SLOT_SIZE, logicalDataOut, minimumRecordSize, OVERFLOW_POINTER_SIZE, OVERFLOW_PTR_FIELD_SIZE, PAGE_HEADER_OFFSET, PAGE_HEADER_SIZE, PAGE_VERSION_OFFSET, rawDataIn, rawDataOut, RECORD_SPACE_OFFSET, SMALL_SLOT_SIZE, spareSpace, totalSpace

Fields inherited from class org.apache.derby.impl.store.raw.data.CachedPage
alreadyReadPage, containerCache, dataFactory, initialRowCount, isDirty, PAGE_FORMAT_ID_SIZE, pageCache, pageData, preDirty, WRITE_NO_SYNC, WRITE_SYNC

Fields inherited from class org.apache.derby.impl.store.raw.data.BasePage
identity, inClean, INIT_PAGE_OVERFLOW, INIT_PAGE_REUSE, INIT_PAGE_REUSE_RECORDID, INVALID_PAGE, LOG_RECORD_DEFAULT, LOG_RECORD_FOR_PURGE, LOG_RECORD_FOR_UPDATE, owner, preLatch, VALID_PAGE

Fields inherited from interface org.apache.derby.iapi.store.raw.Page
DIAG_BYTES_FREE, DIAG_BYTES_RESERVED, DIAG_MAXROWSIZE, DIAG_MINIMUM_REC_SIZE, DIAG_MINROWSIZE, DIAG_NUMOVERFLOWED, DIAG_PAGE_SIZE, DIAG_PAGEOVERHEAD, DIAG_RESERVED_SPACE, DIAG_ROWSIZE, DIAG_SLOTTABLE_SIZE, FIRST_SLOT_NUMBER, INSERT_CONDITIONAL, INSERT_DEFAULT, INSERT_FOR_SPLIT, INSERT_INITIAL, INSERT_OVERFLOW, INSERT_UNDO_WITH_PURGE, INVALID_SLOT_NUMBER

Constructor Summary

Constructors
Constructor Description

AllocPage()

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`addPage(FileContainer mycontainer, long newPageNumber, RawTransaction ntt, BaseContainerHandle userHandle)`	Add a page which is managed by this alloc page.
`boolean`	`canAddFreePage(long lastAllocatedPage)`
`void`	`chainNewAllocPage(BaseContainerHandle allocHandle, long newAllocPageNum, long newAllocPageOffset)`
`protected void`	`chainNextAllocPage(LogInstant instant, long newAllocPageNum, long newAllocPageOffset)`	Chain the next page number and offset underneath a log record
`protected boolean`	`compress(RawTransaction ntt, FileContainer myContainer)`	compress out empty pages at end of container.
`protected void`	`compressSpace(LogInstant instant, int new_highest_page, int num_pages_truncated)`	Compress free pages.
`private AllocExtent`	`createExtent(long pageNum, int pageSize, int pagesAlloced, int availspace)`
`protected void`	`createPage(PageKey newIdentity, PageCreationArgs args)`	Create a new alloc page.
`void`	`deallocatePage(BaseContainerHandle userHandle, long pageNumber)`
`protected AllocExtent`	`getAllocExtent()`	Return a copy of the allocExtent to be cached by the container.
`long`	`getLastPagenum()`
`protected long`	`getLastPreallocPagenum()`
`protected int`	`getMaxFreeSpace()`	The maximum free space on this page possible.
`long`	`getMaxPagenum()`
`long`	`getNextAllocPageNumber()`
`long`	`getNextAllocPageOffset()`
`protected int`	`getPageStatus(long pageNumber)`
`int`	`getTypeFormatId()`	Return my format identifier.
`protected void`	`initFromData(FileContainer myContainer, PageKey newIdentity)`	Initialize in memory structure using the buffer in pageData
`boolean`	`isLast()`
`long`	`nextFreePageNumber(long pnum)`	Return the next free page number after given page number
`protected void`	`preAllocatePage(FileContainer myContainer, int preAllocThreshold, int preAllocSize)`	Preallocate user page if needed.
`private void`	`readAllocPageHeader()`
`static void`	`ReadContainerInfo(byte[] containerInfo, byte[] epage)`	Extract the container information from epage.
`private AllocExtent`	`readExtent(int offset)`
`protected void`	`setPageStatus(LogInstant instant, long pageNumber, int newStatus)`	Do the actual page allocation/deallocation/ree underneath a log operation.
`java.lang.String`	`toString()`	debugging, print this page
`protected void`	`undoCompressSpace(LogInstant instant, int new_highest_page, int num_pages_truncated)`	Handle undo of compress space operation.
`private void`	`updateAllocPageHeader()`
`protected void`	`updateUnfilledPageInfo(AllocExtent inputExtent)`
`static void`	`WriteContainerInfo(byte[] containerInfo, byte[] epage, boolean create)`	Write the container information into the container information area.
`private void`	`writeExtent(int offset)`
`protected void`	`writePage(PageKey identity)`	Write the page out

Methods inherited from class org.apache.derby.impl.store.raw.data.StoredPage
allowInsert, appendOverflowFieldHeader, clearSection, compactRecord, currentTimeStamp, doUpdateAtSlot, entireRecordOnPage, equalTimeStamp, expandPage, fetchNumFieldsAtSlot, getCurrentFreeSpace, getIsOverflow, getNewOverflowPage, getOverflowPage, getOverflowPageForInsert, getOverflowPageForInsert, getOverflowSlot, getPageDumpString, getPageSize, getRecordLength, getRecordPortionLength, getReservedCount, getSlotsInUse, getTotalSpace, initialize, initPage, insertAtSlot, internalDeletedRecordCount, isOverflowPage, logAction, logColumn, logField, logLongColumn, logRecord, logRow, moveRecordForCompressAtSlot, newRecordId, newRecordId, newRecordIdAndBump, purgeOverflowAtSlot, purgeRecord, purgeRowPieces, recordHeaderOnDemand, releaseExclusive, removeOrphanedColumnChain, reserveSpaceForSlot, restorePortionLongColumn, restoreRecordFromSlot, restoreRecordFromStream, setDeleteStatus, setPageStatus, setReservedSpace, setTimeStamp, skipField, skipRecord, spaceForCopy, spaceForCopy, spaceForInsert, spaceForInsert, storeField, storeRecord, toUncheckedString, unfilled, updateChecksum, updateFieldAtSlot, updateFieldOverflowDetails, updateOverflowDetails, updateOverflowed, usePageBuffer, validateChecksum, writeFormatId

Methods inherited from class org.apache.derby.impl.store.raw.data.CachedPage
clean, clearIdentity, createIdentity, getPageArray, isActuallyDirty, isDirty, preDirty, setContainerRowCount, setDirty, setFactory, setIdentity, setPageArray

Methods inherited from class org.apache.derby.impl.store.raw.data.BasePage
bumpPageVersion, bumpRecordCount, cleanPageForReuse, clearLastLogInstant, compactRecord, copyAndPurge, deallocatePage, deleteAtSlot, fetchFieldFromSlot, fetchFromSlot, fetchNumFields, fillInIdentity, findRecordById, getAuxObject, getHeaderAtSlot, getIdentity, getInvalidRecordHandle, getLastLogInstant, getNextSlotNumber, getPageId, getPageKey, getPageNumber, getPageStatus, getPageVersion, getRecordHandle, getRecordHandleAtSlot, getSlotNumber, initializeHeaders, initPage, insert, insertAllowOverflow, insertLongColumn, insertNoOverflow, internalNonDeletedRecordCount, isDeletedAtSlot, isDeletedOnPage, isLatched, isRepositionNeeded, makeRecordHandle, MakeRecordHandle, nonDeletedRecordCount, purgeAtSlot, recordCount, recordExists, removeAndShiftDown, setAuxObject, setDeleteStatus, setExclusive, setExclusiveNoWait, setHeaderAtSlot, setPageStatus, setPageVersion, setRepositionNeeded, shiftUp, shouldReclaimSpace, slotTableToString, unlatch, update, updateAtSlot, updateLastLogInstant

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.apache.derby.iapi.services.cache.Cacheable
getIdentity

- Field Detail
  - FORMAT_NUMBER
```
public static final int FORMAT_NUMBER
```
    See Also:
    
    Constant Field Values
  - 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:
    
    Constant Field Values
  - ALLOC_PAGE_HEADER_SIZE
```
protected static final int ALLOC_PAGE_HEADER_SIZE
```
    See Also:
    
    Constant Field Values
  - BORROWED_SPACE_OFFSET
```
protected static final int BORROWED_SPACE_OFFSET
```
    See Also:
    
    Constant Field Values
  - BORROWED_SPACE_LEN
```
protected static final int BORROWED_SPACE_LEN
```
    See Also:
    
    Constant Field Values
  - MAX_BORROWED_SPACE
```
protected static final int MAX_BORROWED_SPACE
```
    See Also:
    
    Constant Field Values
  - TEST_MULTIPLE_ALLOC_PAGE
```
public static final java.lang.String TEST_MULTIPLE_ALLOC_PAGE
```
    Extent Testing Use these strings to simulate error conditions for testing purposes.
- Constructor Detail
  - AllocPage
```
public AllocPage()
```
- Method Detail
  - 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 java.io.IOException
```
    Throws:
    
    java.io.IOException
  - updateAllocPageHeader
```
private void updateAllocPageHeader()
                            throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - readExtent
```
private AllocExtent readExtent(int offset)
                        throws java.io.IOException,
                               java.lang.ClassNotFoundException
```
    Throws:
    
    java.io.IOException
    
    java.lang.ClassNotFoundException
  - writeExtent
```
private void writeExtent(int offset)
                  throws java.io.IOException
```
    Throws:
    
    java.io.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 java.lang.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.

Class AllocPage

Field Summary

Fields inherited from class org.apache.derby.impl.store.raw.data.StoredPage

Fields inherited from class org.apache.derby.impl.store.raw.data.CachedPage

Fields inherited from class org.apache.derby.impl.store.raw.data.BasePage

Fields inherited from interface org.apache.derby.iapi.store.raw.Page

Constructor Summary

Method Summary

Methods inherited from class org.apache.derby.impl.store.raw.data.StoredPage

Methods inherited from class org.apache.derby.impl.store.raw.data.CachedPage

Methods inherited from class org.apache.derby.impl.store.raw.data.BasePage

Methods inherited from class java.lang.Object

Methods inherited from interface org.apache.derby.iapi.services.cache.Cacheable

Field Detail

FORMAT_NUMBER

nextAllocPageNumber

nextAllocPageOffset

reserved1

reserved2

reserved3

reserved4

extent

borrowedSpace

ALLOC_PAGE_HEADER_OFFSET

ALLOC_PAGE_HEADER_SIZE

BORROWED_SPACE_OFFSET

BORROWED_SPACE_LEN

MAX_BORROWED_SPACE

TEST_MULTIPLE_ALLOC_PAGE

Constructor Detail

AllocPage

Method Detail

getTypeFormatId

getMaxFreeSpace

createPage

createExtent

initFromData

writePage

readAllocPageHeader

updateAllocPageHeader

readExtent

writeExtent

WriteContainerInfo

ReadContainerInfo

nextFreePageNumber

addPage

deallocatePage

updateUnfilledPageInfo

canAddFreePage

getNextAllocPageOffset

chainNewAllocPage

getNextAllocPageNumber

isLast

getLastPagenum

getMaxPagenum

getLastPreallocPagenum

getPageStatus

setPageStatus

chainNextAllocPage

compressSpace

undoCompressSpace

toString

getAllocExtent

preAllocatePage

compress