| /*------------------------------------------------------------------------- | |
| * | |
| * proc.h | |
| * per-process shared memory data structures | |
| * | |
| * | |
| * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group | |
| * Portions Copyright (c) 1994, Regents of the University of California | |
| * | |
| * src/include/storage/proc.h | |
| * | |
| *------------------------------------------------------------------------- | |
| */ | |
| /* | |
| * Each backend advertises up to PGPROC_MAX_CACHED_SUBXIDS TransactionIds | |
| * for non-aborted subtransactions of its current top transaction. These | |
| * have to be treated as running XIDs by other backends. | |
| * | |
| * We also keep track of whether the cache overflowed (ie, the transaction has | |
| * generated at least one subtransaction that didn't fit in the cache). | |
| * If none of the caches have overflowed, we can assume that an XID that's not | |
| * listed anywhere in the PGPROC array is not a running transaction. Else we | |
| * have to look at pg_subtrans. | |
| * | |
| * See src/test/isolation/specs/subxid-overflow.spec if you change this. | |
| */ | |
| typedef struct XidCacheStatus | |
| { | |
| /* number of cached subxids, never more than PGPROC_MAX_CACHED_SUBXIDS */ | |
| uint8 count; | |
| /* has PGPROC->subxids overflowed */ | |
| bool overflowed; | |
| } XidCacheStatus; | |
| struct XidCache | |
| { | |
| TransactionId xids[PGPROC_MAX_CACHED_SUBXIDS]; | |
| }; | |
| /* | |
| * Flags for PGPROC->statusFlags and PROC_HDR->statusFlags[] | |
| */ | |
| /* flags reset at EOXact */ | |
| /* | |
| * Xmin-related flags. Make sure any flags that affect how the process' Xmin | |
| * value is interpreted by VACUUM are included here. | |
| */ | |
| /* | |
| * We allow a small number of "weak" relation locks (AccessShareLock, | |
| * RowShareLock, RowExclusiveLock) to be recorded in the PGPROC structure | |
| * rather than the main lock table. This eases contention on the lock | |
| * manager LWLocks. See storage/lmgr/README for additional details. | |
| */ | |
| /* | |
| * An invalid pgprocno. Must be larger than the maximum number of PGPROC | |
| * structures we could possibly have. See comments for MAX_BACKENDS. | |
| */ | |
| /* | |
| * Flags for PGPROC.delayChkptFlags | |
| * | |
| * These flags can be used to delay the start or completion of a checkpoint | |
| * for short periods. A flag is in effect if the corresponding bit is set in | |
| * the PGPROC of any backend. | |
| * | |
| * For our purposes here, a checkpoint has three phases: (1) determine the | |
| * location to which the redo pointer will be moved, (2) write all the | |
| * data durably to disk, and (3) WAL-log the checkpoint. | |
| * | |
| * Setting DELAY_CHKPT_START prevents the system from moving from phase 1 | |
| * to phase 2. This is useful when we are performing a WAL-logged modification | |
| * of data that will be flushed to disk in phase 2. By setting this flag | |
| * before writing WAL and clearing it after we've both written WAL and | |
| * performed the corresponding modification, we ensure that if the WAL record | |
| * is inserted prior to the new redo point, the corresponding data changes will | |
| * also be flushed to disk before the checkpoint can complete. (In the | |
| * extremely common case where the data being modified is in shared buffers | |
| * and we acquire an exclusive content lock on the relevant buffers before | |
| * writing WAL, this mechanism is not needed, because phase 2 will block | |
| * until we release the content lock and then flush the modified data to | |
| * disk.) | |
| * | |
| * Setting DELAY_CHKPT_COMPLETE prevents the system from moving from phase 2 | |
| * to phase 3. This is useful if we are performing a WAL-logged operation that | |
| * might invalidate buffers, such as relation truncation. In this case, we need | |
| * to ensure that any buffers which were invalidated and thus not flushed by | |
| * the checkpoint are actually destroyed on disk. Replay can cope with a file | |
| * or block that doesn't exist, but not with a block that has the wrong | |
| * contents. | |
| */ | |
| typedef enum | |
| { | |
| PROC_WAIT_STATUS_OK, | |
| PROC_WAIT_STATUS_WAITING, | |
| PROC_WAIT_STATUS_ERROR, | |
| } ProcWaitStatus; | |
| /* | |
| * Each backend has a PGPROC struct in shared memory. There is also a list of | |
| * currently-unused PGPROC structs that will be reallocated to new backends. | |
| * | |
| * links: list link for any list the PGPROC is in. When waiting for a lock, | |
| * the PGPROC is linked into that lock's waitProcs queue. A recycled PGPROC | |
| * is linked into ProcGlobal's freeProcs list. | |
| * | |
| * Note: twophase.c also sets up a dummy PGPROC struct for each currently | |
| * prepared transaction. These PGPROCs appear in the ProcArray data structure | |
| * so that the prepared transactions appear to be still running and are | |
| * correctly shown as holding locks. A prepared transaction PGPROC can be | |
| * distinguished from a real one at need by the fact that it has pid == 0. | |
| * The semaphore and lock-activity fields in a prepared-xact PGPROC are unused, | |
| * but its myProcLocks[] lists are valid. | |
| * | |
| * We allow many fields of this struct to be accessed without locks, such as | |
| * delayChkptFlags and isBackgroundWorker. However, keep in mind that writing | |
| * mirrored ones (see below) requires holding ProcArrayLock or XidGenLock in | |
| * at least shared mode, so that pgxactoff does not change concurrently. | |
| * | |
| * Mirrored fields: | |
| * | |
| * Some fields in PGPROC (see "mirrored in ..." comment) are mirrored into an | |
| * element of more densely packed ProcGlobal arrays. These arrays are indexed | |
| * by PGPROC->pgxactoff. Both copies need to be maintained coherently. | |
| * | |
| * NB: The pgxactoff indexed value can *never* be accessed without holding | |
| * locks. | |
| * | |
| * See PROC_HDR for details. | |
| */ | |
| struct PGPROC | |
| { | |
| /* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */ | |
| dlist_node links; /* list link if process is in a list */ | |
| dlist_head *procgloballist; /* procglobal list that owns this PGPROC */ | |
| PGSemaphore sem; /* ONE semaphore to sleep on */ | |
| ProcWaitStatus waitStatus; | |
| Latch procLatch; /* generic latch for process */ | |
| TransactionId xid; /* id of top-level transaction currently being | |
| * executed by this proc, if running and XID | |
| * is assigned; else InvalidTransactionId. | |
| * mirrored in ProcGlobal->xids[pgxactoff] */ | |
| TransactionId xmin; /* minimal running XID as it was when we were | |
| * starting our xact, excluding LAZY VACUUM: | |
| * vacuum must not remove tuples deleted by | |
| * xid >= xmin ! */ | |
| LocalTransactionId lxid; /* local id of top-level transaction currently | |
| * being executed by this proc, if running; | |
| * else InvalidLocalTransactionId */ | |
| int pid; /* Backend's process ID; 0 if prepared xact */ | |
| int pgxactoff; /* offset into various ProcGlobal->arrays with | |
| * data mirrored from this PGPROC */ | |
| int pgprocno; /* Number of this PGPROC in | |
| * ProcGlobal->allProcs array. This is set | |
| * once by InitProcGlobal(). | |
| * ProcGlobal->allProcs[n].pgprocno == n */ | |
| /* These fields are zero while a backend is still starting up: */ | |
| BackendId backendId; /* This backend's backend ID (if assigned) */ | |
| Oid databaseId; /* OID of database this backend is using */ | |
| Oid roleId; /* OID of role using this backend */ | |
| Oid tempNamespaceId; /* OID of temp schema this backend is | |
| * using */ | |
| bool isBackgroundWorker; /* true if background worker. */ | |
| /* | |
| * While in hot standby mode, shows that a conflict signal has been sent | |
| * for the current transaction. Set/cleared while holding ProcArrayLock, | |
| * though not required. Accessed without lock, if needed. | |
| */ | |
| bool recoveryConflictPending; | |
| /* Info about LWLock the process is currently waiting for, if any. */ | |
| uint8 lwWaiting; /* see LWLockWaitState */ | |
| uint8 lwWaitMode; /* lwlock mode being waited for */ | |
| proclist_node lwWaitLink; /* position in LW lock wait list */ | |
| /* Support for condition variables. */ | |
| proclist_node cvWaitLink; /* position in CV wait list */ | |
| /* Info about lock the process is currently waiting for, if any. */ | |
| /* waitLock and waitProcLock are NULL if not currently waiting. */ | |
| LOCK *waitLock; /* Lock object we're sleeping on ... */ | |
| PROCLOCK *waitProcLock; /* Per-holder info for awaited lock */ | |
| LOCKMODE waitLockMode; /* type of lock we're waiting for */ | |
| LOCKMASK heldLocks; /* bitmask for lock types already held on this | |
| * lock object by this backend */ | |
| pg_atomic_uint64 waitStart; /* time at which wait for lock acquisition | |
| * started */ | |
| int delayChkptFlags; /* for DELAY_CHKPT_* flags */ | |
| uint8 statusFlags; /* this backend's status flags, see PROC_* | |
| * above. mirrored in | |
| * ProcGlobal->statusFlags[pgxactoff] */ | |
| /* | |
| * Info to allow us to wait for synchronous replication, if needed. | |
| * waitLSN is InvalidXLogRecPtr if not waiting; set only by user backend. | |
| * syncRepState must not be touched except by owning process or WALSender. | |
| * syncRepLinks used only while holding SyncRepLock. | |
| */ | |
| XLogRecPtr waitLSN; /* waiting for this LSN or higher */ | |
| int syncRepState; /* wait state for sync rep */ | |
| dlist_node syncRepLinks; /* list link if process is in syncrep queue */ | |
| /* | |
| * All PROCLOCK objects for locks held or awaited by this backend are | |
| * linked into one of these lists, according to the partition number of | |
| * their lock. | |
| */ | |
| dlist_head myProcLocks[NUM_LOCK_PARTITIONS]; | |
| XidCacheStatus subxidStatus; /* mirrored with | |
| * ProcGlobal->subxidStates[i] */ | |
| struct XidCache subxids; /* cache for subtransaction XIDs */ | |
| /* Support for group XID clearing. */ | |
| /* true, if member of ProcArray group waiting for XID clear */ | |
| bool procArrayGroupMember; | |
| /* next ProcArray group member waiting for XID clear */ | |
| pg_atomic_uint32 procArrayGroupNext; | |
| /* | |
| * latest transaction id among the transaction's main XID and | |
| * subtransactions | |
| */ | |
| TransactionId procArrayGroupMemberXid; | |
| uint32 wait_event_info; /* proc's wait information */ | |
| /* Support for group transaction status update. */ | |
| bool clogGroupMember; /* true, if member of clog group */ | |
| pg_atomic_uint32 clogGroupNext; /* next clog group member */ | |
| TransactionId clogGroupMemberXid; /* transaction id of clog group member */ | |
| XidStatus clogGroupMemberXidStatus; /* transaction status of clog | |
| * group member */ | |
| int clogGroupMemberPage; /* clog page corresponding to | |
| * transaction id of clog group member */ | |
| XLogRecPtr clogGroupMemberLsn; /* WAL location of commit record for clog | |
| * group member */ | |
| /* Lock manager data, recording fast-path locks taken by this backend. */ | |
| LWLock fpInfoLock; /* protects per-backend fast-path state */ | |
| uint64 fpLockBits; /* lock modes held for each fast-path slot */ | |
| Oid fpRelId[FP_LOCK_SLOTS_PER_BACKEND]; /* slots for rel oids */ | |
| bool fpVXIDLock; /* are we holding a fast-path VXID lock? */ | |
| LocalTransactionId fpLocalTransactionId; /* lxid for fast-path VXID | |
| * lock */ | |
| /* | |
| * Support for lock groups. Use LockHashPartitionLockByProc on the group | |
| * leader to get the LWLock protecting these fields. | |
| */ | |
| PGPROC *lockGroupLeader; /* lock group leader, if I'm a member */ | |
| dlist_head lockGroupMembers; /* list of members, if I'm a leader */ | |
| dlist_node lockGroupLink; /* my member link, if I'm a member */ | |
| }; | |
| /* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */ | |
| extern PGDLLIMPORT PGPROC *MyProc; | |
| /* | |
| * There is one ProcGlobal struct for the whole database cluster. | |
| * | |
| * Adding/Removing an entry into the procarray requires holding *both* | |
| * ProcArrayLock and XidGenLock in exclusive mode (in that order). Both are | |
| * needed because the dense arrays (see below) are accessed from | |
| * GetNewTransactionId() and GetSnapshotData(), and we don't want to add | |
| * further contention by both using the same lock. Adding/Removing a procarray | |
| * entry is much less frequent. | |
| * | |
| * Some fields in PGPROC are mirrored into more densely packed arrays (e.g. | |
| * xids), with one entry for each backend. These arrays only contain entries | |
| * for PGPROCs that have been added to the shared array with ProcArrayAdd() | |
| * (in contrast to PGPROC array which has unused PGPROCs interspersed). | |
| * | |
| * The dense arrays are indexed by PGPROC->pgxactoff. Any concurrent | |
| * ProcArrayAdd() / ProcArrayRemove() can lead to pgxactoff of a procarray | |
| * member to change. Therefore it is only safe to use PGPROC->pgxactoff to | |
| * access the dense array while holding either ProcArrayLock or XidGenLock. | |
| * | |
| * As long as a PGPROC is in the procarray, the mirrored values need to be | |
| * maintained in both places in a coherent manner. | |
| * | |
| * The denser separate arrays are beneficial for three main reasons: First, to | |
| * allow for as tight loops accessing the data as possible. Second, to prevent | |
| * updates of frequently changing data (e.g. xmin) from invalidating | |
| * cachelines also containing less frequently changing data (e.g. xid, | |
| * statusFlags). Third to condense frequently accessed data into as few | |
| * cachelines as possible. | |
| * | |
| * There are two main reasons to have the data mirrored between these dense | |
| * arrays and PGPROC. First, as explained above, a PGPROC's array entries can | |
| * only be accessed with either ProcArrayLock or XidGenLock held, whereas the | |
| * PGPROC entries do not require that (obviously there may still be locking | |
| * requirements around the individual field, separate from the concerns | |
| * here). That is particularly important for a backend to efficiently checks | |
| * it own values, which it often can safely do without locking. Second, the | |
| * PGPROC fields allow to avoid unnecessary accesses and modification to the | |
| * dense arrays. A backend's own PGPROC is more likely to be in a local cache, | |
| * whereas the cachelines for the dense array will be modified by other | |
| * backends (often removing it from the cache for other cores/sockets). At | |
| * commit/abort time a check of the PGPROC value can avoid accessing/dirtying | |
| * the corresponding array value. | |
| * | |
| * Basically it makes sense to access the PGPROC variable when checking a | |
| * single backend's data, especially when already looking at the PGPROC for | |
| * other reasons already. It makes sense to look at the "dense" arrays if we | |
| * need to look at many / most entries, because we then benefit from the | |
| * reduced indirection and better cross-process cache-ability. | |
| * | |
| * When entering a PGPROC for 2PC transactions with ProcArrayAdd(), the data | |
| * in the dense arrays is initialized from the PGPROC while it already holds | |
| * ProcArrayLock. | |
| */ | |
| typedef struct PROC_HDR | |
| { | |
| /* Array of PGPROC structures (not including dummies for prepared txns) */ | |
| PGPROC *allProcs; | |
| /* Array mirroring PGPROC.xid for each PGPROC currently in the procarray */ | |
| TransactionId *xids; | |
| /* | |
| * Array mirroring PGPROC.subxidStatus for each PGPROC currently in the | |
| * procarray. | |
| */ | |
| XidCacheStatus *subxidStates; | |
| /* | |
| * Array mirroring PGPROC.statusFlags for each PGPROC currently in the | |
| * procarray. | |
| */ | |
| uint8 *statusFlags; | |
| /* Length of allProcs array */ | |
| uint32 allProcCount; | |
| /* Head of list of free PGPROC structures */ | |
| dlist_head freeProcs; | |
| /* Head of list of autovacuum's free PGPROC structures */ | |
| dlist_head autovacFreeProcs; | |
| /* Head of list of bgworker free PGPROC structures */ | |
| dlist_head bgworkerFreeProcs; | |
| /* Head of list of walsender free PGPROC structures */ | |
| dlist_head walsenderFreeProcs; | |
| /* First pgproc waiting for group XID clear */ | |
| pg_atomic_uint32 procArrayGroupFirst; | |
| /* First pgproc waiting for group transaction status update */ | |
| pg_atomic_uint32 clogGroupFirst; | |
| /* WALWriter process's latch */ | |
| Latch *walwriterLatch; | |
| /* Checkpointer process's latch */ | |
| Latch *checkpointerLatch; | |
| /* Current shared estimate of appropriate spins_per_delay value */ | |
| int spins_per_delay; | |
| /* Buffer id of the buffer that Startup process waits for pin on, or -1 */ | |
| int startupBufferPinWaitBufId; | |
| } PROC_HDR; | |
| extern PGDLLIMPORT PROC_HDR *ProcGlobal; | |
| extern PGDLLIMPORT PGPROC *PreparedXactProcs; | |
| /* Accessor for PGPROC given a pgprocno. */ | |
| /* | |
| * We set aside some extra PGPROC structures for auxiliary processes, | |
| * ie things that aren't full-fledged backends but need shmem access. | |
| * | |
| * Background writer, checkpointer, WAL writer and archiver run during normal | |
| * operation. Startup process and WAL receiver also consume 2 slots, but WAL | |
| * writer is launched only after startup has exited, so we only need 5 slots. | |
| */ | |
| /* configurable options */ | |
| extern PGDLLIMPORT int DeadlockTimeout; | |
| extern PGDLLIMPORT int StatementTimeout; | |
| extern PGDLLIMPORT int LockTimeout; | |
| extern PGDLLIMPORT int IdleInTransactionSessionTimeout; | |
| extern PGDLLIMPORT int IdleSessionTimeout; | |
| extern PGDLLIMPORT bool log_lock_waits; | |
| /* | |
| * Function Prototypes | |
| */ | |
| extern int ProcGlobalSemas(void); | |
| extern Size ProcGlobalShmemSize(void); | |
| extern void InitProcGlobal(void); | |
| extern void InitProcess(void); | |
| extern void InitProcessPhase2(void); | |
| extern void InitAuxiliaryProcess(void); | |
| extern void SetStartupBufferPinWaitBufId(int bufid); | |
| extern int GetStartupBufferPinWaitBufId(void); | |
| extern bool HaveNFreeProcs(int n, int *nfree); | |
| extern void ProcReleaseLocks(bool isCommit); | |
| extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable); | |
| extern void ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus); | |
| extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock); | |
| extern void CheckDeadLockAlert(void); | |
| extern bool IsWaitingForLock(void); | |
| extern void LockErrorCleanup(void); | |
| extern void ProcWaitForSignal(uint32 wait_event_info); | |
| extern void ProcSendSignal(int pgprocno); | |
| extern PGPROC *AuxiliaryPidGetProc(int pid); | |
| extern void BecomeLockGroupLeader(void); | |
| extern bool BecomeLockGroupMember(PGPROC *leader, int pid); | |