org.neo4j.io.pagecache

Interface Page

public interface Page

A page in the page cache. Always represents a concrete page in memory, and may represent a particular page in a file, if that file-page has been swapped into the page.

Method Summary

Methods

Modifier and Type	Method and Description
int	swapIn(StoreChannel channel, long offset, int length) Swap a file-page into memory.
void	swapOut(StoreChannel channel, long offset, int length) Swap the page out to storage.

Method Detail

swapIn

int swapIn(StoreChannel channel,
         long offset,
         int length)
           throws IOException

Swap a file-page into memory. The file-page location is given by the offset into the file represented by the StoreChannel, and the length. The contents of the page in the file is unchanged by this operation. May throw an AssertionError or a RuntimeException if the given length is greater than the cache-page size. 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.

Throws:

IOException - If the file could not be read from. For instance, if the file has been closed, moved or deleted, or if the requested range of data goes beyond the length of the file. The possible causes of an IOException is platform dependent. If the channel has been closed, then it must be reopened and the swapIn operation must be retried.

swapOut

void swapOut(StoreChannel channel,
           long offset,
           int length)
             throws IOException

Swap the page out to storage. The contents of the current page is written to the file represented by the given StoreChannel, at the location expressed by the given offset into the file, and the length. The contents of the page in memory are unchanged by this operation. May throw an AssertionError or a RuntimeException if the length is greater than the cache-page size. If the offset is greater than the length of the file, the space in between will be filled with null-bytes. Note: This only performs the write on the OS level. No forcing of the StoreChannel is implied.

Throws:

IOException - If the file could not be written to. For instance, if the storage device is out of space, or the file has been moved or deleted. The possible causes of an IOException is platform dependent. If the channel has been closed, then it must be reopened and the swapIn operation must be retried.