ProvSQL C/C++ API
Adding support for provenance and uncertainty management to PostgreSQL databases
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MMappedUUIDHashTable Class Reference

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

#include "MMappedUUIDHashTable.h"

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Classes

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

Public Member Functions

 MMappedUUIDHashTable (const char *filename, bool read_only, uint64_t magic)
 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 38 of file MMappedUUIDHashTable.h.

Constructor & Destructor Documentation

◆ MMappedUUIDHashTable()

MMappedUUIDHashTable::MMappedUUIDHashTable ( const char * filename,
bool read_only,
uint64_t magic )

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

Parameters
filenamePath to the backing file (created if absent).
read_onlyIf true, map the file read-only (no new entries can be inserted).
magicExpected magic value for format validation.

Definition at line 35 of file MMappedUUIDHashTable.cpp.

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◆ ~MMappedUUIDHashTable()

MMappedUUIDHashTable::~MMappedUUIDHashTable ( )

Sync and unmap the file.

Definition at line 116 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
uUUID to insert.
Returns
A pair {value, inserted} where inserted is true if a new entry was created.

Definition at line 140 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
uUUID to look up.
Returns
Slot index, or NOTHING if u is not in the table.

Definition at line 122 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 90 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
uUUID to hash.
Returns
Slot index in [0, capacity).

Definition at line 110 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
lengthNumber of bytes to map.
read_onlyIf true, map read-only.

Definition at line 77 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 175 of file MMappedUUIDHashTable.h.

◆ operator[]()

unsigned long MMappedUUIDHashTable::operator[] ( pg_uuid_t u) const

Look up the integer index for UUID u.

Parameters
uThe UUID to look up.
Returns
The associated integer, or NOTHING if u is absent.

Definition at line 133 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
uUUID key to store.
iInteger value to associate with u.

Definition at line 157 of file MMappedUUIDHashTable.cpp.

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◆ sync()

void MMappedUUIDHashTable::sync ( )

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

Definition at line 162 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 94 of file MMappedUUIDHashTable.h.

◆ MAXIMUM_LOAD_FACTOR

double MMappedUUIDHashTable::MAXIMUM_LOAD_FACTOR =.5
staticconstexprprivate

Rehash when this fraction of slots is occupied.

Definition at line 100 of file MMappedUUIDHashTable.h.

◆ NOTHING

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

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

Definition at line 137 of file MMappedUUIDHashTable.h.

◆ STARTING_LOG_SIZE

unsigned MMappedUUIDHashTable::STARTING_LOG_SIZE =16
staticconstexprprivate

Initial log2 capacity (65 536 slots).

Definition at line 98 of file MMappedUUIDHashTable.h.

◆ table

table_t* MMappedUUIDHashTable::table
private

Pointer to the memory-mapped table header.

Definition at line 95 of file MMappedUUIDHashTable.h.

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