CacheAccessor Class Reference

CacheAccessor defines the subset of the Cache interface used for accessing cache pages. More...

#include <CacheAccessor.h>

Inheritance diagram for CacheAccessor:

List of all members.

Public Member Functions
virtual	~CacheAccessor ()
virtual CachePage *	lockPage (BlockId blockId, LockMode lockMode, bool readIfUnmapped=true, MappedPageListener *pMappedPageListener=NULL, TxnId txnId=IMPLICIT_TXN_ID)=0
	Locks a page into memory with the specified concurrency mode.
virtual void	unlockPage (CachePage &page, LockMode lockMode, TxnId txnId=IMPLICIT_TXN_ID)=0
	Releases lock held on page.
virtual void	discardPage (BlockId blockId)=0
	Unmaps a page from the cache if already mapped, discarding its contents if dirty.
virtual bool	prefetchPage (BlockId blockId, MappedPageListener *pMappedPageListener=NULL)=0
	Hints that a page should be prefetched in preparation for a future lock request.
virtual void	prefetchBatch (BlockId blockId, uint nPages, MappedPageListener *pMappedPageListener=NULL)=0
	Hints that a contiguous run of pages should be prefetched.
virtual void	flushPage (CachePage &page, bool async)=0
	Forces the contents of a dirty page to its mapped location.
virtual void	nicePage (CachePage &page)=0
	Marks a page as nice, indicating that it is very unlikely the page's mapping will be needed again any time soon, so it is a good candidate for victimization.
virtual uint	getMaxLockedPages ()=0
	Returns: the page lock quota on this accessor
virtual void	setMaxLockedPages (uint nPages)=0
	Sets the page lock quota on this accessor.
virtual SharedCache	getCache ()=0
	Returns: the underlying Cache accessed by this CacheAccessor
virtual void	setTxnId (TxnId txnId)=0
	Sets a default TxnId to use for locking pages (to be used when IMPLICIT_TXN_ID is specified).
virtual TxnId	getTxnId () const=0
	Returns: default TxnId associated with this accessor
virtual void	getPrefetchParams (uint &prefetchPagesMax, uint &prefetchThrottleRate)=0
	Retrieves the current pre-fetch caching parameters that determine how many pages should be pre-fetched and how often the pre-fetches should occur.

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Detailed Description

CacheAccessor defines the subset of the Cache interface used for accessing cache pages.

This allows page usage to be associated with particular consumers such as connections, algorithms, etc. The Cache interface is derived from CacheAccessor, so any Cache implementation can alway be used directly as a vanilla CacheAccessor.

Definition at line 41 of file CacheAccessor.h.

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Constructor & Destructor Documentation

CacheAccessor::~CacheAccessor

(

)

[virtual]

Definition at line 38 of file Cache.cpp.

{
}

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Member Function Documentation

virtual CachePage* CacheAccessor::lockPage	(	BlockId	blockId,
		LockMode	lockMode,
		bool	readIfUnmapped = true,
		MappedPageListener *	pMappedPageListener = NULL,
		TxnId	txnId = IMPLICIT_TXN_ID
	)			[pure virtual]

Locks a page into memory with the specified concurrency mode.

When the page contents are no longer needed, the caller must invoke the unlockPage() method with the same concurrency mode to release it. If the desired page is already locked by another thread with an incompatible concurrency mode, blocks until the page becomes available (unless the lock mode is of the NoWait variety, in which case returns NULL immediately). Note that NoWait locking only applies to lock contention, not I/O, so if an unmapped page is locked in NoWait mode, blocks until the read completes.

The device referenced by the requested blockId must already be registered with the cache and must remain registered for the duration of the lock.

Notes on concurrency modes:

• LOCKMODE_S: Acquire a shared lock on page.

• LOCKMODE_X: Acquire an exclusive lock on page. Note that this does not mark the page dirty, although an exclusive lock is mandatory before a page can be used for write access. When an exclusive lock is already held, the same thread may acquire a shared lock, but not vice versa (such an upgrade would make deadlock possible).

• LOCKMODE_S_NOWAIT: Attempt to acquire a shared lock on page, but fail immediately if this would conflict with an exclusive lock already held by another thread.

• LOCKMODE_X_NOWAIT: Attempt to acquire an exclusive lock on page, but fail immediately if this would conflict with a shared or exclusive lock already held by another thread.

Parameters:

	blockId	the BlockId of the page to be locked
	lockMode	the desired concurrency mode
	readIfUnmapped	if true (the default) the page data is read as part of mapping; if false, the page data is left invalid until first write (used when allocating a new block with invalid contents)
	pMappedPageListener	optional listener to receive notifications when this page is written; if specified, it must match all prior and subsequent lock requests for the same page mapping
	txnId	optional TxnId to associate with lock; default is IMPLICIT_TXN_ID, which uses current thread ID as an implicit TxnId

Returns:

the locked CachePage, or NULL if a NoWait attempt failed

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, QuotaCacheAccessor, TransactionalCacheAccessor, and ScratchSegment.

Referenced by CacheTest::lockPage().

virtual void CacheAccessor::unlockPage	(	CachePage &	page,
		LockMode	lockMode,
		TxnId	txnId = IMPLICIT_TXN_ID
	)			[pure virtual]

Releases lock held on page.

Parameters:

	page	the page to be unlocked
	lockMode	must correspond to value passed to Cache::lockPage; however, for pages locked with NOWAIT, the equivalent unlock type should be normal (e.g. LOCKMODE_S instead of LOCKMODE_S_NOWAIT)
	txnId	must correspond to value passed to Cache::lockPage

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, QuotaCacheAccessor, TransactionalCacheAccessor, and ScratchSegment.

Referenced by PagingTestBase::testScratch(), SegmentTestBase::unlockPage(), and CacheTest::unlockPage().

virtual void CacheAccessor::discardPage

(

BlockId

blockId

)

[pure virtual]

Unmaps a page from the cache if already mapped, discarding its contents if dirty.

The caller must ensure that no other thread has the page locked.

Parameters:

blockId

the BlockId of the page to be discarded

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, and ScratchSegment.

virtual bool CacheAccessor::prefetchPage	(	BlockId	blockId,
		MappedPageListener *	pMappedPageListener = NULL
	)			[pure virtual]

Hints that a page should be prefetched in preparation for a future lock request.

Parameters:

	blockId	the BlockId of the page to be prefetched
	pMappedPageListener	optional listener to receive notifications when this page is written; if specified, it must match all prior and subsequent lock requests for the same page mapping

Returns:

true if the pre-fetch request was successful

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, and ScratchSegment.

Referenced by SegmentTestBase::prefetchPage(), and CacheTest::prefetchPage().

virtual void CacheAccessor::prefetchBatch	(	BlockId	blockId,
		uint	nPages,
		MappedPageListener *	pMappedPageListener = NULL
	)			[pure virtual]

Hints that a contiguous run of pages should be prefetched.

Parameters:

	blockId	the BlockId of the first page to be prefetched; more will be prefetched depending on the configured batch size
	nPages	number of pages in batch
	pMappedPageListener	optional listener to receive notifications when this page is written; if specified, it must match all prior and subsequent lock requests for the same page mapping

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, and ScratchSegment.

Referenced by CacheTest::prefetchBatch().

virtual void CacheAccessor::flushPage	(	CachePage &	page,
		bool	async
	)			[pure virtual]

Forces the contents of a dirty page to its mapped location.

Page must already be locked in exclusive mode. For an asynchronous flush, the caller must ensure that the page contents remain unchanged until the flush completes.

Parameters:

	page	the page to be flushed
	async	true to schedle async write and return immediately; false to wait for write to complete

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, and ScratchSegment.

virtual void CacheAccessor::nicePage

(

CachePage &

page

)

[pure virtual]

Marks a page as nice, indicating that it is very unlikely the page's mapping will be needed again any time soon, so it is a good candidate for victimization.

Parameters:

page

the page to be marked

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, and ScratchSegment.

Referenced by PagingTestBase::testOp().

virtual uint CacheAccessor::getMaxLockedPages

(

)

[pure virtual]

Returns:

the page lock quota on this accessor

Implemented in Cache, DelegatingCacheAccessor, QuotaCacheAccessor, and ScratchSegment.

virtual void CacheAccessor::setMaxLockedPages

(

uint

nPages

)

[pure virtual]

Sets the page lock quota on this accessor.

Ignored for accessor implementations that don't support quotas.

Parameters:

nPages

new quota

Implemented in Cache, DelegatingCacheAccessor, QuotaCacheAccessor, and ScratchSegment.

virtual SharedCache CacheAccessor::getCache

(

)

[pure virtual]

Returns:

the underlying Cache accessed by this CacheAccessor

Implemented in Cache, DelegatingCacheAccessor, and ScratchSegment.

virtual void CacheAccessor::setTxnId

(

TxnId

txnId

)

[pure virtual]

Sets a default TxnId to use for locking pages (to be used when IMPLICIT_TXN_ID is specified).

Not all CacheAccessor implementations support this behavior.

Parameters:

txnId

new default txn ID

Implemented in Cache, DelegatingCacheAccessor, TransactionalCacheAccessor, and ScratchSegment.

virtual TxnId CacheAccessor::getTxnId

(

)

const [pure virtual]

Returns:

default TxnId associated with this accessor

Implemented in Cache, DelegatingCacheAccessor, TransactionalCacheAccessor, and ScratchSegment.

virtual void CacheAccessor::getPrefetchParams	(	uint &	prefetchPagesMax,
		uint &	prefetchThrottleRate
	)			[pure virtual]

Retrieves the current pre-fetch caching parameters that determine how many pages should be pre-fetched and how often the pre-fetches should occur.

Parameters:

[out]	prefetchPagesMax	max number of outstanding pre-fetch pages
[out]	prefetchThrottleRate	the number of successful pre-fetches that have to occur before the pre-fetch rate is throttled back up, in the event that it has been throttled down due to rejected requests

Implemented in CacheImpl< PageT, VictimPolicyT >, DelegatingCacheAccessor, and ScratchSegment.

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The documentation for this class was generated from the following files:

• /home/pub/open/dev/fennel/cache/CacheAccessor.h
• /home/pub/open/dev/fennel/cache/Cache.cpp

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