alloc_cache_t Class Reference

Free-Page allocation/deallocation interface. More...

#include <alloc_cache.h>

Public Member Functions
	alloc_cache_t (stnode_cache_t &stcache, bool virgin, bool clustered)
rc_t	sx_allocate_page (PageID &pid, StoreID stid=0)
rc_t	sx_deallocate_page (PageID pid)
rc_t	sx_format_alloc_page (PageID alloc_pid)
bool	is_allocated (PageID pid)
PageID	get_last_allocated_pid (StoreID s) const
	Returns last allocated PID of a given store. More...
PageID	get_last_allocated_pid () const
	Returns last allocated PID of ALL stores. More...
PageID	_get_last_allocated_pid_internal () const
lsn_t	get_page_lsn (PageID pid)

Static Public Member Functions
static bool	is_alloc_pid (PageID pid)

Static Public Attributes
static constexpr size_t	extent_size = alloc_page::bits_held

Private Member Functions
rc_t	load_alloc_page (StoreID stid, extent_id_t ext)

Private Attributes
std::vector< PageID >	last_alloc_page
stnode_cache_t &	stcache
srwlock_t	_latch

Detailed Description

Free-Page allocation/deallocation interface.

This object handles allocation/deallocation requests for one volume. All allocation/deallocation are logged and done in a critical section. To make it scalable, this object is designed to be as fast as possible.

See also

alloc_page_h

Constructor & Destructor Documentation

alloc_cache_t()

alloc_cache_t::alloc_cache_t	(	stnode_cache_t &	stcache,
		bool	virgin,
		bool	clustered
	)

Member Function Documentation

_get_last_allocated_pid_internal()

PageID alloc_cache_t::_get_last_allocated_pid_internal

(

)

const

get_last_allocated_pid() [1/2]

PageID alloc_cache_t::get_last_allocated_pid

(

StoreID

s

)

const

Returns last allocated PID of a given store.

get_last_allocated_pid() [2/2]

PageID alloc_cache_t::get_last_allocated_pid

(

)

const

Returns last allocated PID of ALL stores.

get_page_lsn()

lsn_t alloc_cache_t::get_page_lsn

(

PageID

pid

)

is_alloc_pid()

static bool alloc_cache_t::is_alloc_pid ( PageID  pid )

inlinestatic

is_allocated()

bool alloc_cache_t::is_allocated

(

PageID

pid

)

load_alloc_page()

rc_t alloc_cache_t::load_alloc_page ( StoreID  stid, extent_id_t  ext  )

private

Reads the alloc page of given extent to update last_alloc_page

sx_allocate_page()

rc_t alloc_cache_t::sx_allocate_page	(	PageID &	pid,
		StoreID	stid = 0
	)

Allocates one page. (System transaction)

Parameters

[out]	pid	allocated page ID.
[in]	stid	StoreID to which this page will belong – this is used for clustering pages of the same store in the same extents

sx_deallocate_page()

rc_t alloc_cache_t::sx_deallocate_page

(

PageID

pid

)

Deallocates one page. (System transaction)

Parameters

[in]

pid

page ID to deallocate.

sx_format_alloc_page()

rc_t alloc_cache_t::sx_format_alloc_page

(

PageID

alloc_pid

)

Formats an alloc page for a new extent. Called internally in sx_allocate_page.

Member Data Documentation

_latch

srwlock_t alloc_cache_t::_latch

mutableprivate

This lath protects access to last_alloc_page

extent_size

constexpr size_t alloc_cache_t::extent_size = alloc_page::bits_held

static

last_alloc_page

std::vector<PageID> alloc_cache_t::last_alloc_page

private

Keep track of free pages using the ID of the last allocated page and a list of free pages whose IDs are lower than that.

Pages which are freed end up in the list of freed pages, again one for each store. Currently, these lists are only used to determine whether a certain page is allocated or not. To avoid fragmentation in a workload with many deletions, items should be removed from these lists when allocating a page to avoid fragmentation. One extreme policy would be to only use the contiguous space when the corresponding list is empty, i.e., when the non-contiguous space has been fully utilized. Policies that trade off allocation performance for fragmentation by managing allocations from both contiguous and non-contiguous space would be the more flexible and robust option.

In Feb 2017, this was extended to support clustering pages by store ID, which requires assigning extents to stores exclusively, which means that we must keep track of page allocation on a per-store basis.

stcache

stnode_cache_t& alloc_cache_t::stcache

private

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

• src/sm/alloc_cache.h
• src/sm/alloc_cache.cpp