org.neo4j.io.pagecache

Interface PageSwapper

public interface PageSwapper

Implementation note: These methods must NEVER swallow a thread-interrupt. If the thread is interrupted when these methods are called, or gets interrupted while they are executing, then they must either throw an InterruptedException, or leave the interrupted-status flag alone.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close and release all resources associated with the file underlying this PageSwapper.
void	evicted(long pageId, Page page) Notification that a page has been evicted, used to clean up state in structures outside the page table.
File	file() Get the file that this PageSwapper represents.
void	force() Forces all writes done by this PageSwapper to the underlying storage device, such that the writes are durable when this call returns.
long	getLastPageId() Get the filePageId of the last page in the concrete file.
long	read(long filePageId, Page page) Read the page with the given filePageId, from the concrete file on the file system, into the given page.
long	read(long startFilePageId, Page[] pages, int arrayOffset, int length) Read pages from the file into the given pages, starting from the given startFilePageId.
void	truncate() Truncate the file represented by this PageSwapper, so the size of the file is zero and getLastPageId() returns -1.
long	write(long filePageId, Page page) Write the contents of the given page, to the concrete file on the file system, at the located indicated by the given filePageId.
long	write(long startFilePageId, Page[] pages, int arrayOffset, int length) Write the contents of the given pages, to the concrete file on the file system, starting at the location of the given startFilePageId.

Method Detail

read

long read(long filePageId,
        Page page)
          throws IOException

Read the page with the given filePageId, from the concrete file on the file system, into the given page. Returns the number of bytes read in from the file. May be zero if the requested page was beyond the end of the file. If less than the file page size, then the rest of the page will contain zeros. Note: It is possible for the channel to be asynchronously closed while this operation is taking place. For instance, if the current thread is interrupted. If this happens, then the implementation must reopen the channel and the operation must be retried.

Throws:

IOException

read

long read(long startFilePageId,
        Page[] pages,
        int arrayOffset,
        int length)
          throws IOException

Read pages from the file into the given pages, starting from the given startFilePageId. Returns the number of bytes read in from the file. May be zero if the requested startFilePageId was beyond the end of the file. If the file does not have enough data to fill up all the buffer space represented by the pages, then the remaining buffer space will be filled with zero bytes. The contents of the pages should be considered to be garbage if the operation throws an exception, since the constituent reads can be reordered, and no zeroing will take place. Note: It is possible for the channel to be asynchronously closed while this operation is taking place. For instance, if the current thread is interrupted. If this happens, then the implementation must reopen the channel and the operation must be retried.

Throws:

IOException

write

long write(long filePageId,
         Page page)
           throws IOException

Write the contents of the given page, to the concrete file on the file system, at the located indicated by the given filePageId. Returns the number of bytes written to the file. Note: It is possible for the channel to be asynchronously closed while this operation is taking place. For instance, if the current thread is interrupted. If this happens, then implementation must reopen the channel and the operation must be retried.

Throws:

IOException

write

long write(long startFilePageId,
         Page[] pages,
         int arrayOffset,
         int length)
           throws IOException

Write the contents of the given pages, to the concrete file on the file system, starting at the location of the given startFilePageId. If an exception is thrown, then some of the data may have been written, and some might not. The writes may reorder and tear, so no guarantee can be made about what has been written and what has not, if an exception is thrown. Therefor, the entire write operation should be retried, in the case of failure, or the data should be rewritten through other means. Returns the number of bytes written to the file. Note: It is possible for the channel to be asynchronously closed while this operation is taking place. For instance, if the current thread is interrupted. If this happens, then implementation must reopen the channel and the operation must be retried.

Throws:

IOException

evicted

void evicted(long pageId,
           Page page)

Notification that a page has been evicted, used to clean up state in structures outside the page table.

file

File file()

Get the file that this PageSwapper represents.

close

void close()
           throws IOException

Close and release all resources associated with the file underlying this PageSwapper.

Throws:

IOException

force

void force()
           throws IOException

Forces all writes done by this PageSwapper to the underlying storage device, such that the writes are durable when this call returns. This method has no effect if the PageSwapperFactory.syncDevice() method forces the writes for all non-closed PageSwappers created through the given PageSwapperFactory. The PageCache.flushAndForce() method will first call force on the PageSwappers for all mapped files, then call syncDevice on the PageSwapperFactory. This way, the writes are always made durable regardless of which method that does the forcing.

Throws:

IOException

getLastPageId

long getLastPageId()
                   throws IOException

Get the filePageId of the last page in the concrete file.

Throws:

IOException

truncate

void truncate()
              throws IOException

Truncate the file represented by this PageSwapper, so the size of the file is zero and getLastPageId() returns -1. Truncation may occur concurrently with writes, in which case both operations will appear to be atomic, such that either the write happens before the truncation and is lost, or the file is truncated and the write then extends the file with any zero padding and the written data.

Throws:

IOException