org.neo4j.io.pagecache

Interface PageCache

All Superinterfaces:

AutoCloseable

public interface PageCache
extends AutoCloseable

A page caching mechanism that allows caching multiple files and accessing their data in pages via a re-usable cursor.

This interface does not specify the cache eviction and allocation behavior, it may be backed by implementations that map entire files into RAM, or implementations with smart eviction strategies, trying to keep "hot" pages in RAM.

Method Summary

Modifier and Type	Method and Description
void	close() Flush all dirty pages and close the page cache.
void	flushAndForce() Flush all dirty pages
void	flushAndForce(IOLimiter limiter) Flush all dirty pages, but limit the rate of IO as advised by the given IOPSLimiter.
PagedFile	map(File file, int pageSize, OpenOption... openOptions) Ask for a handle to a paged file, backed by this page cache.
int	maxCachedPages() The max number of cached pages.
int	pageSize() The size in bytes of the pages managed by this cache.

Method Detail

map

PagedFile map(File file,
              int pageSize,
              OpenOption... openOptions)
       throws IOException

Ask for a handle to a paged file, backed by this page cache.

Note that this currently asks for the pageSize to use, which is an artifact or records being of varying size in the stores. This should be consolidated to use a standard page size for the whole cache, with records aligning on those page boundaries.

Parameters:

file - The file to map.

pageSize - The file page size to use for this mapping. If the file is already mapped with a different page size, an exception will be thrown.

openOptions - The set of open options to use for mapping this file. The StandardOpenOption.READ and StandardOpenOption.WRITE options always implicitly specified. The StandardOpenOption.CREATE open option will create the given file if it does not already exist, and the StandardOpenOption.TRUNCATE_EXISTING will truncate any existing file iff it has not already been mapped. The StandardOpenOption.DELETE_ON_CLOSE will cause the file to be deleted after the last unmapping. The PageCacheOpenOptions.EXCLUSIVE will cause the map method to throw if the file is already mapped. Otherwise, the file will be mapped exclusively, and subsequent attempts at mapping the file will fail with an exception until the exclusively mapped file is closed. All other options are either silently ignored, or will cause an exception to be thrown.

Throws:

NoSuchFileException - if the given file does not exist, and the StandardOpenOption.CREATE option was not specified.

IOException - if the file could otherwise not be mapped. Causes include the file being locked, or exclusive mapping conflicts.

flushAndForce

void flushAndForce()
            throws IOException

Flush all dirty pages

Throws:

IOException

flushAndForce

void flushAndForce(IOLimiter limiter)
            throws IOException

Flush all dirty pages, but limit the rate of IO as advised by the given IOPSLimiter.

Parameters:

limiter - The IOLimiter that determines if pauses or sleeps should be injected into the flushing process to keep the IO rate down.

Throws:

IOException

close

void close()
    throws IOException

Flush all dirty pages and close the page cache.

Specified by:

close in interface AutoCloseable

Throws:

IOException

pageSize

int pageSize()

The size in bytes of the pages managed by this cache.

maxCachedPages

int maxCachedPages()

The max number of cached pages.