provsql_mmap.h File Reference

Background worker and IPC primitives for mmap-backed circuit storage. More...

#include "limits.h"
#include <unistd.h>
#include "postgres.h"
#include "provsql_utils.h"
#include "provsql_config.h"

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Classes
struct	provsql_cleanup_result
	What provsql.circuit_cleanup() reports. More...

Macros
#define	PROVSQL_STORE_FLUSH_INTERVAL_MS   200
	How long the worker waits after a write before forcing the store to stable storage.
#define	READM(var, type)
	Read one value of type from the background-to-main pipe.
#define	READB(var, type)
	Read one value of type from the main-to-background pipe.
#define	WRITEB(pvar, type)
	Write one value of type to the main-to-background pipe.
#define	WRITEM(pvar, type)
	Write one value of type to the background-to-main pipe.
#define	READB_BYTES(ptr, n)
	Read exactly n bytes of a reply from the main-to-background pipe.
#define	READM_BYTES(ptr, n)
	Read exactly n bytes of a request from the background-to-main pipe.
#define	WRITEB_BYTES(ptr, n)
	Write n reply bytes to the main-to-background pipe.
#define	STARTWRITEM()
	Reset the shared write buffer for a new batched write.
#define	ADDWRITEM(pvar, type)
	Append one value of type to the shared write buffer.
#define	SENDWRITEM()
	Flush the shared write buffer to the background-to-main pipe atomically.
#define	ADDWRITEDB()
	Append the per-message database header to the write buffer.

Enumerations
enum	provsql_set_prob_result { PROVSQL_SET_PROB_NOT_PROB_GATE = 0 , PROVSQL_SET_PROB_WRITTEN = 1 , PROVSQL_SET_PROB_UNCHANGED = 2 , PROVSQL_SET_PROB_ALREADY_SET = 3 }
	Outcome of a probability write, mirroring MMappedCircuit::SetProbResult across the IPC boundary. More...

Functions
void	provsql_mmap_worker (Datum)
	Entry point for the ProvSQL mmap background worker.
void	RegisterProvSQLMMapWorker (void)
	Register the ProvSQL mmap background worker with PostgreSQL.
void	initialize_provsql_mmap (void)
	Initialise the circuit store.
void	destroy_provsql_mmap (void)
	Unmap and close the mmap files.
void	provsql_mmap_main_loop (void)
	Main processing loop of the mmap background worker.
void	provsql_circuit_cleanup_request (bool dry_run, const pg_uuid_t *roots, int64 nb_roots, provsql_cleanup_result *out)
	Ask the worker to rebuild this database's store, keeping only what roots reach.
void	provsql_store_flush (void)
	Force every open circuit to stable storage.
void	provsql_store_note_write (void)
	Note that this transaction has written to the circuit store.
bool	provsql_store_written (void)
	Whether this transaction has written to the circuit store.
void	provsql_mmap_dispatch (char c, Oid db_oid, Oid db_tablespace)
	Handle a single IPC message: read its payload and write its reply.
void	provsql_internal_create_gate (const pg_uuid_t *token, gate_type type, unsigned nb_children, const pg_uuid_t *children_data)
	Create a gate from in-extension C/C++ code (cache + worker IPC).
void	provsql_internal_create_gate_with (const pg_uuid_t *token, gate_type type, unsigned nb_children, const pg_uuid_t *children, bool has_infos, unsigned info1, unsigned info2, const char *extra)
	Create a gate together with its infos and its text, in one message that is not answered.
provsql_set_prob_result	provsql_internal_set_prob (const pg_uuid_t *token, double prob, double *existing)
	Write a gate's probability from in-extension C/C++ code.
void	provsql_internal_clear_prob (const pg_uuid_t *token)
	Drop a gate's probability, leaving it as it was before anyone wrote one.
bool	provsql_internal_get_prob_written (const pg_uuid_t *token, double *prob)
	Report whether a probability has been written on a gate.
gate_type	provsql_fetch_gate (const pg_uuid_t *token, unsigned *nb_children_out, pg_uuid_t **children_out)
	Fetch a gate's type and children, cache-first with a worker round-trip (and cache fill) on a miss.
bool	provsql_read_all (int fd, void *dst, size_t n)
	Read exactly n bytes from fd into dst; false on EOF/error.
bool	provsql_worker_read (void *dst, size_t n)
	The worker's buffered read of the request pipe: what the pipe holds is read in one call, and the messages are parsed from the buffer.
bool	provsql_worker_buffered (void)
	Whether the worker's read buffer holds unread bytes, which poll() cannot see.

Variables
char	buffer [PIPE_BUF]
	Shared write buffer used with STARTWRITEM / ADDWRITEM / SENDWRITEM.
unsigned	bufferpos
	Current write position within buffer.

Detailed Description

Background worker and IPC primitives for mmap-backed circuit storage.

ProvSQL persists the provenance circuit in memory-mapped files so that data survives transaction boundaries and is shared across backend processes. Because multiple backends may create gates concurrently, a dedicated PostgreSQL background worker (provsql_mmap_worker) is the sole writer to those files; normal backends communicate with it through a pair of anonymous pipes described in provsqlSharedState.

This header exposes:

• Functions to register, start, and manage the background worker.
• A set of pipe I/O macros (READM, READB, WRITEB, WRITEM) that wrap read()/write() calls on the inter-process pipes.
• A buffered-write interface (STARTWRITEM, ADDWRITEM, SENDWRITEM) that batches multiple fields into a single write() to stay within the atomic PIPE_BUF guarantee.

Definition in file provsql_mmap.h.

Macro Definition Documentation

ADDWRITEDB

#define ADDWRITEDB

(

)

Value:

(ADDWRITEM(&MyDatabaseId, Oid), ADDWRITEM(&MyDatabaseTableSpace, Oid))

Append the per-message database header to the write buffer.

Every request carries the OID of the database it applies to and the OID of that database's default tablespace, so the worker – which runs outside any transaction and cannot read pg_database – can resolve the directory holding the backing files. Follows the opcode byte in every message.

Definition at line 325 of file provsql_mmap.h.

ADDWRITEM

#define ADDWRITEM	(		pvar,
			type )

Value:

(memcpy(buffer+bufferpos, pvar, sizeof(type)), bufferpos+=sizeof(type))

Append one value of type to the shared write buffer.

Definition at line 310 of file provsql_mmap.h.

PROVSQL_STORE_FLUSH_INTERVAL_MS

#define PROVSQL_STORE_FLUSH_INTERVAL_MS   200

How long the worker waits after a write before forcing the store to stable storage.

The circuit store is outside PostgreSQL's WAL, so a committed transaction's gates can still be sitting in the kernel's page cache when the machine loses power. Forcing them out this long after the last write bounds the loss, the way synchronous_commit = off bounds the heap's; provsql.synchronous_commit removes it entirely, at the price of one flush per store-writing transaction.

Definition at line 84 of file provsql_mmap.h.

READB

#define READB	(		var,
			type )

Value:

(read(provsql_shared_state->pipembr, &var, sizeof(type))==(ssize_t)sizeof(type))

Read one value of type from the main-to-background pipe.

Definition at line 294 of file provsql_mmap.h.

READB_BYTES

#define READB_BYTES	(		ptr,
			n )

Value:

provsql_read_all(provsql_shared_state->pipembr, (ptr), (n))

Read exactly n bytes of a reply from the main-to-background pipe.

Definition at line 301 of file provsql_mmap.h.

READM

#define READM	(		var,
			type )

Value:

provsql_worker_read(&var, sizeof(type))

Read one value of type from the background-to-main pipe.

Definition at line 292 of file provsql_mmap.h.

READM_BYTES

#define READM_BYTES	(		ptr,
			n )

Value:

provsql_worker_read((ptr), (n))

Read exactly n bytes of a request from the background-to-main pipe.

Definition at line 303 of file provsql_mmap.h.

SENDWRITEM

#define SENDWRITEM

(

)

Value:

(write(provsql_shared_state->pipebmw, buffer, bufferpos)!=-1)

Flush the shared write buffer to the background-to-main pipe atomically.

Definition at line 312 of file provsql_mmap.h.

STARTWRITEM

#define STARTWRITEM

(

)

Value:

(bufferpos=0)

Reset the shared write buffer for a new batched write.

Definition at line 308 of file provsql_mmap.h.

WRITEB

#define WRITEB	(		pvar,
			type )

Value:

(write(provsql_shared_state->pipembw, pvar, sizeof(type))!=-1)

Write one value of type to the main-to-background pipe.

Definition at line 296 of file provsql_mmap.h.

WRITEB_BYTES

#define WRITEB_BYTES	(		ptr,
			n )

Value:

(write(provsql_shared_state->pipembw, (ptr), (n))!=-1)

Write n reply bytes to the main-to-background pipe.

Definition at line 305 of file provsql_mmap.h.

WRITEM

#define WRITEM	(		pvar,
			type )

Value:

(write(provsql_shared_state->pipebmw, pvar, sizeof(type))!=-1)

Write one value of type to the background-to-main pipe.

Definition at line 298 of file provsql_mmap.h.

Enumeration Type Documentation

provsql_set_prob_result

enum provsql_set_prob_result

Outcome of a probability write, mirroring MMappedCircuit::SetProbResult across the IPC boundary.

Enumerator
PROVSQL_SET_PROB_NOT_PROB_GATE	The gate carries no probability.
PROVSQL_SET_PROB_WRITTEN	Written; undo on rollback.
PROVSQL_SET_PROB_UNCHANGED	Already held exactly this value.
PROVSQL_SET_PROB_ALREADY_SET	Holds a different value; refused.

Definition at line 174 of file provsql_mmap.h.

Function Documentation

destroy_provsql_mmap()

void destroy_provsql_mmap

(

void

)

Unmap and close the mmap files.

Called by the background worker on shutdown to release resources and ensure all dirty pages are synced to disk via msync().

Definition at line 86 of file MMappedCircuit.cpp.

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initialize_provsql_mmap()

void initialize_provsql_mmap

(

void

)

Initialise the circuit store.

Called once by the background worker at startup. The per-database files themselves are opened lazily, on the first message for their database.

Definition at line 81 of file MMappedCircuit.cpp.

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provsql_circuit_cleanup_request()

void provsql_circuit_cleanup_request	(	bool	dry_run,
		const pg_uuid_t *	roots,
		int64	nb_roots,
		provsql_cleanup_result *	out )

Ask the worker to rebuild this database's store, keeping only what roots reach.

The caller must hold the database exclusively; see provsql.circuit_cleanup in circuit_cleanup.c.

Definition at line 287 of file provsql_mmap.c.

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provsql_fetch_gate()

gate_type provsql_fetch_gate	(	const pg_uuid_t *	token,
		unsigned *	nb_children_out,
		pg_uuid_t **	children_out )

Fetch a gate's type and children, cache-first with a worker round-trip (and cache fill) on a miss.

On return *children_out is a calloc'd array to be freed by the caller, or NULL when the gate has no children.

Fetch a gate's type and children, cache-first with a worker round-trip (and cache fill) on a miss.

On cache miss this fetches BOTH the gate type and its children from the worker, in one critical section, then caches them together. If we cached only the type (with an empty children list), a subsequent get_children() call for the same token would consult the cache, find the entry, and return 0 children : never querying the worker for the real children. provsql.provenance_evaluate hits exactly that pattern (it calls get_gate_type first, then unnest(get_children(...))) and silently folds plus/times gates over an empty set.

Fetch a gate's type and children, cache-first with a worker round-trip (and cache fill) on a miss. Factored out of the get_gate_type() wrapper for in-extension callers that walk the circuit from C (e.g. the annotation-transparent set_prob()). On return *children_out is a calloc'd array to be freed by the caller, or NULL when the gate has no children.

Definition at line 456 of file provsql_mmap.c.

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provsql_internal_clear_prob()

void provsql_internal_clear_prob

(

const pg_uuid_t *

token

)

Drop a gate's probability, leaving it as it was before anyone wrote one.

The rollback path of probability_store.c, and the only way to unset a probability: there is none from SQL. Unlike a write it does not arm the at-commit sync barrier – it runs when the transaction that would have committed is already gone.

Definition at line 679 of file provsql_mmap.c.

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provsql_internal_create_gate()

void provsql_internal_create_gate	(	const pg_uuid_t *	token,
		gate_type	type,
		unsigned	nb_children,
		const pg_uuid_t *	children_data )

Create a gate from in-extension C/C++ code (cache + worker IPC).

Internal entry point behind the SQL-callable create_gate(), without Datum marshalling or gate-type-OID lookups; idempotent on already-mapped tokens.

Parameters

token	UUID of the gate.
type	Gate type.
nb_children	Number of children.
children_data	Child UUIDs (may be NULL when nb_children is 0).

Create a gate from in-extension C/C++ code (cache + worker IPC).

Factored out of the SQL-callable wrapper so in-extension C/C++ code (e.g. the decomposition-aligned reachability materialiser) can create gates without Datum marshalling or gate-type-OID lookups. Same semantics: write-through to the per-session cache, then the C message to the background worker; MMappedCircuit::createGate is idempotent on already-mapped tokens.

Definition at line 545 of file provsql_mmap.c.

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provsql_internal_create_gate_with()

void provsql_internal_create_gate_with	(	const pg_uuid_t *	token,
		gate_type	type,
		unsigned	nb_children,
		const pg_uuid_t *	children,
		bool	has_infos,
		unsigned	info1,
		unsigned	info2,
		const char *	extra )

Create a gate together with its infos and its text, in one message that is not answered.

For the gates whose address determines what they record (a value gate and its text, an annotation, a comparison and its operator, an aggregate), so that the write-once rule has nothing to refuse and nobody needs to wait for its answer. extra NULL records no text; has_infos false records no infos.

Definition at line 706 of file provsql_mmap.c.

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provsql_internal_get_prob_written()

bool provsql_internal_get_prob_written	(	const pg_uuid_t *	token,
		double *	prob )

Report whether a probability has been written on a gate.

Distinct from get_prob(), which reports the value an evaluation would use and so answers 1 for a gate nobody gave a probability.

Parameters

token	UUID of the gate.
prob	On true return, the written probability.

Definition at line 684 of file provsql_mmap.c.

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provsql_internal_set_prob()

provsql_set_prob_result provsql_internal_set_prob	(	const pg_uuid_t *	token,
		double	prob,
		double *	existing )

Write a gate's probability from in-extension C/C++ code.

Probabilities are written once (see MMappedCircuit::setProb), so this reports which of the four cases applied rather than a bare success flag. Callers that write a probability on a gate they have just created can treat anything but PROVSQL_SET_PROB_NOT_PROB_GATE as success; set_prob() itself raises on PROVSQL_SET_PROB_ALREADY_SET.

Note that this is the raw store operation: it does not record the write in the transaction's undo list. SQL-level writers go through provsql_set_prob_tracked() in probability_store.c so a rollback drops what they wrote.

Parameters

token	UUID of the gate.
prob	Probability value in [0,1], or NaN to clear.
existing	On PROVSQL_SET_PROB_ALREADY_SET, the stored value.

Definition at line 672 of file provsql_mmap.c.

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provsql_mmap_dispatch()

void provsql_mmap_dispatch	(	char	c,
		Oid	db_oid,
		Oid	db_tablespace )

Handle a single IPC message: read its payload and write its reply.

The opcode c and the message header (db_oid and the database's default tablespace db_tablespace) have already been consumed by the caller. Shared by the background-worker main loop (multi-process build) and the synchronous in-process dispatcher.

Definition at line 499 of file MMappedCircuit.cpp.

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provsql_mmap_main_loop()

void provsql_mmap_main_loop

(

void

)

Main processing loop of the mmap background worker.

Waits for gate-creation requests from backend processes, processes them by writing to the mmap files, and handles SIGTERM for graceful shutdown.

Definition at line 860 of file MMappedCircuit.cpp.

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provsql_mmap_worker()

void provsql_mmap_worker

(

Datum

ignored

)

Entry point for the ProvSQL mmap background worker.

Called by the postmaster when it launches the background worker. Enters the main loop (provsql_mmap_main_loop()) and never returns normally. The single Datum argument is required by the background-worker API but is not used.

Definition at line 146 of file provsql_mmap.c.

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provsql_read_all()

bool provsql_read_all	(	int	fd,
		void *	dst,
		size_t	n )

Read exactly n bytes from fd into dst; false on EOF/error.

Definition at line 111 of file provsql_mmap.c.

provsql_store_flush()

void provsql_store_flush

(

void

)

Force every open circuit to stable storage.

Definition at line 492 of file MMappedCircuit.cpp.

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provsql_store_note_write()

void provsql_store_note_write

(

void

)

Note that this transaction has written to the circuit store.

Arms the at-commit sync barrier (provsql.synchronous_commit) and the PREPARE TRANSACTION refusal.

Definition at line 273 of file provsql_mmap.c.

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provsql_store_written()

bool provsql_store_written

(

void

)

Whether this transaction has written to the circuit store.

Definition at line 282 of file provsql_mmap.c.

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provsql_worker_buffered()

bool provsql_worker_buffered

(

void

)

Whether the worker's read buffer holds unread bytes, which poll() cannot see.

Definition at line 80 of file provsql_mmap.c.

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provsql_worker_read()

bool provsql_worker_read	(	void *	dst,
		size_t	n )

The worker's buffered read of the request pipe: what the pipe holds is read in one call, and the messages are parsed from the buffer.

false on EOF or error.

Definition at line 85 of file provsql_mmap.c.

RegisterProvSQLMMapWorker()

void RegisterProvSQLMMapWorker

(

void

)

Register the ProvSQL mmap background worker with PostgreSQL.

Must be called from the extension's _PG_init() function so that the postmaster starts the worker on the next connection.

Definition at line 162 of file provsql_mmap.c.

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Variable Documentation

buffer

char buffer[PIPE_BUF]

extern

Shared write buffer used with STARTWRITEM / ADDWRITEM / SENDWRITEM.

Definition at line 69 of file provsql_mmap.c.

bufferpos

unsigned bufferpos

extern

Current write position within buffer.

Definition at line 70 of file provsql_mmap.c.