MMappedUUIDHashTable Class Reference

Persistent open-addressing hash table mapping UUIDs to integers. More...

#include "MMappedUUIDHashTable.h"

Collaboration diagram for MMappedUUIDHashTable:

Classes
struct	table_t
	On-disk layout of the hash table stored in the mmap file. More...
struct	value_t
	One slot in the hash table: a UUID key and its associated integer value. More...

Public Member Functions
	MMappedUUIDHashTable (const char *filename, bool read_only)
	Open (or create) the mmap-backed hash table.
	~MMappedUUIDHashTable ()
	Sync and unmap the file.
unsigned long	operator[] (pg_uuid_t u) const
	Look up the integer index for UUID u.
std::pair< unsigned long, bool >	add (pg_uuid_t u)
	Insert UUID u, assigning it the next available integer.
unsigned long	nbElements () const
	Return the number of UUID→integer pairs currently stored.
void	sync ()
	Flush dirty pages to the backing file with msync().

Static Public Attributes
static constexpr unsigned long	NOTHING =static_cast<unsigned long>(-1)
	Sentinel returned by operator[]() when the UUID is not present.

Private Member Functions
unsigned long	hash (pg_uuid_t u) const
	Compute the starting slot index for UUID u.
unsigned long	find (pg_uuid_t u) const
	Find the slot index of u, or NOTHING if absent.
void	mmap (size_t length, bool read_only)
	Map length bytes from the backing file (read-write or read-only).
void	grow ()
	Double the table capacity and rehash all existing entries.
void	set (pg_uuid_t u, unsigned long i)
	Store the mapping u → i in the table.

Private Attributes
int	fd
	File descriptor of the backing mmap file.
table_t *	table
	Pointer to the memory-mapped table header.

Static Private Attributes
static constexpr unsigned	STARTING_LOG_SIZE =16
	Initial log2 capacity (65 536 slots).
static constexpr double	MAXIMUM_LOAD_FACTOR =.5
	Rehash when this fraction of slots is occupied.

Detailed Description

Persistent open-addressing hash table mapping UUIDs to integers.

Definition at line 37 of file MMappedUUIDHashTable.h.

Constructor & Destructor Documentation

MMappedUUIDHashTable()

MMappedUUIDHashTable::MMappedUUIDHashTable	(	const char *	filename,
		bool	read_only
	)

Open (or create) the mmap-backed hash table.

Parameters

filename	Path to the backing file (created if absent).
read_only	If true, map the file read-only (no new entries can be inserted).

Definition at line 33 of file MMappedUUIDHashTable.cpp.

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~MMappedUUIDHashTable()

MMappedUUIDHashTable::~MMappedUUIDHashTable

(

)

Sync and unmap the file.

Definition at line 102 of file MMappedUUIDHashTable.cpp.

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Member Function Documentation

add()

std::pair< unsigned long, bool > MMappedUUIDHashTable::add

(

pg_uuid_t

u

)

Insert UUID u, assigning it the next available integer.

If u is already present the existing value is returned without modification.

Parameters

u	UUID to insert.

Returns

A pair {value, inserted} where inserted is true if a new entry was created.

Definition at line 126 of file MMappedUUIDHashTable.cpp.

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find()

unsigned long MMappedUUIDHashTable::find ( pg_uuid_t  u ) const

private

Find the slot index of u, or NOTHING if absent.

Parameters

u	UUID to look up.

Returns

Slot index, or NOTHING if u is not in the table.

Definition at line 108 of file MMappedUUIDHashTable.cpp.

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grow()

void MMappedUUIDHashTable::grow ( )

private

Double the table capacity and rehash all existing entries.

Definition at line 76 of file MMappedUUIDHashTable.cpp.

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hash()

unsigned long MMappedUUIDHashTable::hash ( pg_uuid_t  u ) const

inlineprivate

Compute the starting slot index for UUID u.

Reinterprets the first 8 bytes of u as a 64-bit integer and takes it modulo the current capacity.

Parameters

u	UUID to hash.

Returns

Slot index in [0, capacity).

Definition at line 105 of file MMappedUUIDHashTable.h.

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mmap()

void MMappedUUIDHashTable::mmap ( size_t  length, bool  read_only  )

private

Map length bytes from the backing file (read-write or read-only).

Parameters

length	Number of bytes to map.
read_only	If true, map read-only.

Definition at line 63 of file MMappedUUIDHashTable.cpp.

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nbElements()

unsigned long MMappedUUIDHashTable::nbElements ( ) const

inline

Return the number of UUID→integer pairs currently stored.

Returns

Element count.

Definition at line 169 of file MMappedUUIDHashTable.h.

operator[]()

unsigned long MMappedUUIDHashTable::operator[]

(

pg_uuid_t

u

)

const

Look up the integer index for UUID u.

Parameters

u	The UUID to look up.

Returns

The associated integer, or NOTHING if u is absent.

Definition at line 119 of file MMappedUUIDHashTable.cpp.

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set()

void MMappedUUIDHashTable::set ( pg_uuid_t  u, unsigned long  i  )

private

Store the mapping u → i in the table.

Parameters

u	UUID key to store.
i	Integer value to associate with u.

Definition at line 143 of file MMappedUUIDHashTable.cpp.

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sync()

void MMappedUUIDHashTable::sync

(

)

Flush dirty pages to the backing file with msync().

Definition at line 148 of file MMappedUUIDHashTable.cpp.

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Member Data Documentation

fd

int MMappedUUIDHashTable::fd

private

File descriptor of the backing mmap file.

Definition at line 89 of file MMappedUUIDHashTable.h.

MAXIMUM_LOAD_FACTOR

constexpr double MMappedUUIDHashTable::MAXIMUM_LOAD_FACTOR =.5

staticconstexprprivate

Rehash when this fraction of slots is occupied.

Definition at line 95 of file MMappedUUIDHashTable.h.

NOTHING

constexpr unsigned long MMappedUUIDHashTable::NOTHING =static_cast<unsigned long>(-1)

staticconstexpr

Sentinel returned by operator[]() when the UUID is not present.

Definition at line 132 of file MMappedUUIDHashTable.h.

STARTING_LOG_SIZE

constexpr unsigned MMappedUUIDHashTable::STARTING_LOG_SIZE =16

staticconstexprprivate

Initial log2 capacity (65 536 slots).

Definition at line 93 of file MMappedUUIDHashTable.h.

table

table_t* MMappedUUIDHashTable::table

private

Pointer to the memory-mapped table header.

Definition at line 90 of file MMappedUUIDHashTable.h.

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

• /home/pierre/git/software/provsql/src/MMappedUUIDHashTable.h
• /home/pierre/git/software/provsql/src/MMappedUUIDHashTable.cpp