Page evictioner for the buffer pool. More...

#include <page_evictioner.hpp>

Inheritance diagram for zero::buffer_pool::PageEvictioner:

Public Member Functions
	PageEvictioner (const BufferPool *bufferPool)
	Constructs an abstract page evictioner. More...

	PageEvictioner (const PageEvictioner &)=delete
	Explicitly deleted copy constructor of an abstract page evictioner. More...

PageEvictioner &	operator= (const PageEvictioner &)=delete
	Explicitly deleted assignment operator of an abstract page evictioner. More...

virtual	~PageEvictioner ()
	Destructs an abstract page evictioner. More...

virtual bf_idx	pickVictim () noexcept=0
	Selects a page to be evicted from the buffer pool. More...

virtual void	updateOnPageHit (bf_idx idx) noexcept=0
	Updates the eviction statistics on page hit. More...

virtual void	updateOnPageUnfix (bf_idx idx) noexcept=0
	Updates the eviction statistics on page unfix. More...

virtual void	updateOnPageMiss (bf_idx idx, PageID pid) noexcept=0
	Updates the eviction statistics on page miss. More...

virtual void	updateOnPageFixed (bf_idx idx) noexcept=0
	Updates the eviction statistics of fixed (i.e. used) pages during eviction. More...

virtual void	updateOnPageDirty (bf_idx idx) noexcept=0
	Updates the eviction statistics of dirty pages during eviction. More...

virtual void	updateOnPageBlocked (bf_idx idx) noexcept=0
	Updates the eviction statistics of pages that cannot be evicted at all. More...

virtual void	updateOnPageSwizzled (bf_idx idx) noexcept=0
	Updates the eviction statistics of pages containing swizzled pointers during eviction. More...

virtual void	updateOnPageExplicitlyUnbuffered (bf_idx idx) noexcept=0
	Updates the eviction statistics on explicit unbuffer. More...

virtual void	updateOnPointerSwizzling (bf_idx idx) noexcept=0
	Updates the eviction statistics of pages when its pointer got swizzled in its parent page. More...

virtual void	releaseInternalLatches () noexcept=0
	Releases the internal latches. More...

bool	evictOne (bf_idx &victim)
	Evicts a page from the buffer pool. More...

Public Member Functions inherited from worker_thread_t
	worker_thread_t (int inverval_ms=-1)

virtual	~worker_thread_t ()

void	wakeup (bool wait=false, int rounds_to_wait=-1)

void	stop ()

void	wait_for_round (long round=0)

long	get_rounds_completed () const

bool	is_busy () const

Public Member Functions inherited from thread_wrapper_t
	thread_wrapper_t ()

virtual	~thread_wrapper_t ()

virtual void	before_run ()

virtual void	after_run ()

void	spawn ()

void	fork ()

void	join ()

Protected Member Functions
bool	_doEviction (bf_idx victim) noexcept
	Evicts a page from the buffer pool. More...

Protected Member Functions inherited from worker_thread_t
bool	should_exit () const

void	notify_one ()

void	notify_all ()

void	quit ()

Protected Attributes
const bool	_maintainEMLSN
	Maintain the page's EMLSNs on eviction. More...

const bool	_flushDirty
	Flush dirty pages. More...

const bool	_logEvictions
	Log page evictions. More...

const uint_fast32_t	_evictionBatchSize
	Target value of free buffer frames. More...

const uint_fast32_t	_maxAttempts
	Maximum number of unsuccessful picks of eviction victims. More...

const uint_fast32_t	_wakeupCleanerAttempts = 42
	Number of unsuccessful picks of eviction victims before waking up the page cleaner. More...

Static Protected Attributes
static constexpr bool	_enabledSwizzling = POINTER_SWIZZLER::usesPointerSwizzling
	Pointer swizzling used in the buffer pool. More...

Private Member Functions
bool	_unswizzleAndUpdateEMLSN (bf_idx victim) noexcept
	Unswizzles the pointer in the parent page and updates the EMLSN of that page. More...

void	_flushDirtyPage (const bf_tree_cb_t &victimControlBlock) noexcept
	Flush the specified page. More...

void	do_work () override
	Function evicting pages in the eviction thread. More...

Detailed Description

Page evictioner for the buffer pool.

This is the abstract class for page eviction which implements common functionality required for all page evictioners independent of the used algorithm. All those page evictioners should inherit from this class.

Note: This class is strongly coupled to the buffer pool and some other components of Zero. The inheriting page evictioners implementing specific page eviction algorithms do not need to be coupled to all those components but should just rely on the implementations of evictOne(), _unswizzleAndUpdateEMLSN(), _flushDirtyPage() and do_work().

Constructor & Destructor Documentation

§ PageEvictioner() [1/2]

zero::buffer_pool::PageEvictioner::PageEvictioner ( const BufferPool * bufferPool )

explicit

Constructs an abstract page evictioner.

This constructor initializes the member variables according to specifications of the BufferPool and settings from the sm_options.

Note: Due to the fact that this is a constructor of an abstract class, this can only be called from within the member initializer list of a constructor of an inheriting class.

Parameters

bufferPool The buffer pool this page evictioner is responsible for.

§ PageEvictioner() [2/2]

zero::buffer_pool::PageEvictioner::PageEvictioner ( const PageEvictioner & )

delete

Explicitly deleted copy constructor of an abstract page evictioner.

The copy constructor of an abstract page evictioner is explicitly removed because a page evictioner depends on its corresponding buffer pool and there can only be one buffer pool per Zero instance.

§ ~PageEvictioner()

zero::buffer_pool::PageEvictioner::~PageEvictioner ( )

virtual

Destructs an abstract page evictioner.

Member Function Documentation

§ _doEviction()

zero::buffer_pool::PageEvictioner::_doEviction ( bf_idx victim )

protectednoexcept

Evicts a page from the buffer pool.

Evicts the page from the specified buffer pool frame by:

Unswizzling its pointer in its parent (if needed)
Updating its EMLSN (if needed)
Preparing the corresponding bf_tree_cb_t for the eviction
Flushing the page to the database (if needed and allowed)
Logging the eviction (if supposed to)
Adding the page for recovery (if NoDB is used)
Removing the page from the Hashtable
Releasing the latch of the buffer frame

Postcondition: The buffer frame at index victim is not used (if this is successful) and it is not latched. If _flushDirty is set and if the page was dirty, the page is flushed to the database and if _logEvictions is set, a log record of type evict_page_log is in the log.

Parameters

victim The index of the buffer frame from which the page should be evicted.

Returns: Returns true if the page could successfully be evicted, otherwise false .

§ _flushDirtyPage()

zero::buffer_pool::PageEvictioner::_flushDirtyPage ( const bf_tree_cb_t & victimControlBlock )

privatenoexcept

Flush the specified page.

Writes the specified page to the database file.

Precondition: Specified bf_tree_cb_t is latched in exclusive mode and corresponds to a used buffer frame.

Parameters

victimControlBlock The control block that corresponds to the buffer frame whose contained page gets flushed.

§ _unswizzleAndUpdateEMLSN()

zero::buffer_pool::PageEvictioner::_unswizzleAndUpdateEMLSN ( bf_idx victim )

privatenoexcept

Unswizzles the pointer in the parent page and updates the EMLSN of that page.

In case swizzling is enabled, this unswizzles the pointer in the parent page. Additionally, this updates the parent EMLSN. This two operations are kept in a single method because both require looking up the parent, latching, etc., so we save some work.

Parameters

victim The buffer frame index where the page that gets evicted can be found.

Returns: true if the updates to the parent page were successfully completed and not required, false otherwise.

§ do_work()

zero::buffer_pool::PageEvictioner::do_work ( )

overrideprivatevirtual

Function evicting pages in the eviction thread.

Runs in the eviction thread (executed when the eviction thread gets woken up and when terminated it terminates the eviction thread) and evicts pages as long as there are not _evictionBatchSize free buffer frames in the BufferPool.

Implements worker_thread_t.

§ evictOne()

zero::buffer_pool::PageEvictioner::evictOne ( bf_idx & victim )

Evicts a page from the buffer pool.

Selects a page for eviction and executes the eviction of it.

Parameters

[out] victim The index of the buffer frame from which the page was evicted.

Returns: Returns true if the victim could successfully be evicted, otherwise false .

§ operator=()

zero::buffer_pool::PageEvictioner::operator= ( const PageEvictioner & )

delete

Explicitly deleted assignment operator of an abstract page evictioner.

The assignment operator of an abstract page evictioner is explicitly removed because a page evictioner depends on its corresponding buffer pool and there can only be one buffer pool per Zero instance.

§ pickVictim()

zero::buffer_pool::PageEvictioner::pickVictim ( )

pure virtualnoexcept

Selects a page to be evicted from the buffer pool.

Selects a page to be evicted according to the selected page eviction strategy.

Postcondition: The picked victim is latched in latch_mode_t::LATCH_EX mode as the buffer pool frame will be changed during eviction (page will be removed).

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Returns: The buffer frame that can be freed or 0 if no eviction victim could be found.

Implemented in zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ releaseInternalLatches()

zero::buffer_pool::PageEvictioner::releaseInternalLatches ( )

pure virtualnoexcept

Releases the internal latches.

Some methods of page evictioners hold internal latches beyond the invocation of one method but expect another method to be called later to release those internal latches. This should be used to explicitly release those latches.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageBlocked()

zero::buffer_pool::PageEvictioner::updateOnPageBlocked ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics of pages that cannot be evicted at all.

Updates the statistics according to the selected page eviction strategy when a page cannot be evicted at all.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool which corresponding frame contains a page that cannot be evicted at all.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageDirty()

zero::buffer_pool::PageEvictioner::updateOnPageDirty ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics of dirty pages during eviction.

Updates the statistics according to the selected page eviction strategy when a page was discovered dirty during eviction.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool that was picked for eviction while the corresponding frame contained a dirty page.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, and zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >.

§ updateOnPageExplicitlyUnbuffered()

zero::buffer_pool::PageEvictioner::updateOnPageExplicitlyUnbuffered ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics on explicit unbuffer.

Updates the statistics according to the selected page eviction strategy when a page got explicitly unbuffered.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool whose corresponding frame is freed explicitly.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageFixed()

zero::buffer_pool::PageEvictioner::updateOnPageFixed ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics of fixed (i.e. used) pages during eviction.

Updates the statistics according to the selected page eviction strategy when a page was discovered fixed during eviction.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool that was picked for eviction while the corresponding frame was fixed.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageHit()

zero::buffer_pool::PageEvictioner::updateOnPageHit ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics on page hit.

Updates the statistics according to the selected page eviction strategy when a page hit occurred.

Warning: If a page eviction strategy is sensitive to recognizing the same page reference multiple times, implement this different from updateOnPageUnfix().

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool on which a page hit occurred.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageMiss()

zero::buffer_pool::PageEvictioner::updateOnPageMiss	(	bf_idx	idx,
		PageID	pid
	)

pure virtualnoexcept

Updates the eviction statistics on page miss.

Updates the statistics according to the selected page eviction strategy when a page miss occurred.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool on which a page miss occurred.
pid	The PageID of the generic_page that was loaded into the buffer frame with index `idx` .

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageSwizzled()

zero::buffer_pool::PageEvictioner::updateOnPageSwizzled ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics of pages containing swizzled pointers during eviction.

Updates the statistics according to the selected page eviction strategy when a page was discovered containing swizzled pointers during eviction.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool that was picked for eviction while the corresponding frame contained a page with swizzled pointers.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPageUnfix()

zero::buffer_pool::PageEvictioner::updateOnPageUnfix ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics on page unfix.

Updates the statistics according to the selected page eviction strategy when a page unfix occurred.

Warning: If a page eviction strategy is sensitive to recognizing the same page reference multiple times, implement this different from updateOnPageHit().

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool on which a page unfix occurred.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

§ updateOnPointerSwizzling()

zero::buffer_pool::PageEvictioner::updateOnPointerSwizzling ( bf_idx idx )

pure virtualnoexcept

Updates the eviction statistics of pages when its pointer got swizzled in its parent page.

Updates the statistics according to the selected page eviction strategy when the pointer of a page got swizzled in its parent page.

Note: This member function must be implemented by every specific page evictioner which inherits from this abstract page evictioner.

Parameters

idx	The buffer frame index of the BufferPool whose pointer got swizzled in its corresponding parent page.

Implemented in zero::buffer_pool::PageEvictionerCAR< on_page_unfix >, zero::buffer_pool::PageEvictionerSelectAndFilter< selector_class, filter_class, filter_early >, and zero::buffer_pool::PageEvictionerLeanStore< cooling_stage_size_ppm >.

Member Data Documentation

§ _enabledSwizzling

zero::buffer_pool::PageEvictioner::_enabledSwizzling = POINTER_SWIZZLER::usesPointerSwizzling

staticprotected

Pointer swizzling used in the buffer pool.

Set if the BufferPool uses pointer swizzling for page references.

§ _evictionBatchSize

zero::buffer_pool::PageEvictioner::_evictionBatchSize

protected

Target value of free buffer frames.

Once page evictioning is started, it runs till there are this many free buffer frames in the BufferPool.

§ _flushDirty

zero::buffer_pool::PageEvictioner::_flushDirty

protected

Flush dirty pages.

Set if dirty pages should be flushed when they get evicted from the buffer pool.

§ _logEvictions

zero::buffer_pool::PageEvictioner::_logEvictions

protected

Log page evictions.

Set if a log record should be created for each eviction of a page.

§ _maintainEMLSN

zero::buffer_pool::PageEvictioner::_maintainEMLSN

protected

Maintain the page's EMLSNs on eviction.

Set if the EMLSNs of the pages should be maintained.

§ _maxAttempts

zero::buffer_pool::PageEvictioner::_maxAttempts

protected

Maximum number of unsuccessful picks of eviction victims.

Maximum number of picks of pages in a row that cannot be evicted before an error ("Eviction got stuck!") is thrown.

§ _wakeupCleanerAttempts

zero::buffer_pool::PageEvictioner::_wakeupCleanerAttempts = 42

protected

Number of unsuccessful picks of eviction victims before waking up the page cleaner.

Number of picks of pages in a row that cannot be evicted before the page cleaner of the BufferPool gets woken up (BufferPool::wakeupPageCleaner()).

Remarks: Dirty pages that need to get cleaned are a typical reason for stuck page evictions.

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

src/sm/page_evictioner.hpp
src/sm/page_evictioner.cpp

Public Member Functions

Protected Member Functions

Protected Attributes

Static Protected Attributes

Private Member Functions

Detailed Description

Constructor & Destructor Documentation

§ PageEvictioner() [1/2]

§ PageEvictioner() [2/2]

§ ~PageEvictioner()

Member Function Documentation

§ _doEviction()

§ _flushDirtyPage()

§ _unswizzleAndUpdateEMLSN()

§ do_work()

§ evictOne()

§ operator=()

§ pickVictim()

§ releaseInternalLatches()

§ updateOnPageBlocked()

§ updateOnPageDirty()

§ updateOnPageExplicitlyUnbuffered()

§ updateOnPageFixed()

§ updateOnPageHit()

§ updateOnPageMiss()

§ updateOnPageSwizzled()

§ updateOnPageUnfix()

§ updateOnPointerSwizzling()

Member Data Documentation

§ _enabledSwizzling

§ _evictionBatchSize

§ _flushDirty

§ _logEvictions

§ _maintainEMLSN

§ _maxAttempts

§ _wakeupCleanerAttempts