proc.h

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/*-------------------------------------------------------------------------
 *
 * proc.h
 *    per-process shared memory data structures
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/storage/proc.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef _PROC_H_
#define _PROC_H_

#include "access/clog.h"
#include "access/xlogdefs.h"
#include "lib/ilist.h"
#include "storage/latch.h"
#include "storage/lock.h"
#include "storage/pg_sema.h"
#include "storage/proclist_types.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.
 */
#define PGPROC_MAX_CACHED_SUBXIDS 64    /* XXX guessed-at value */

struct XidCache
{
    TransactionId xids[PGPROC_MAX_CACHED_SUBXIDS];
};

/*
 * Flags for PGXACT->vacuumFlags
 *
 * Note: If you modify these flags, you need to modify PROCARRAY_XXX flags
 * in src/include/storage/procarray.h.
 *
 * PROC_RESERVED may later be assigned for use in vacuumFlags, but its value is
 * used for PROCARRAY_SLOTS_XMIN in procarray.h, so GetOldestXmin won't be able
 * to match and ignore processes with this flag set.
 */
#define     PROC_IS_AUTOVACUUM  0x01    /* is it an autovac worker? */
#define     PROC_IN_VACUUM      0x02    /* currently running lazy vacuum */
#define     PROC_VACUUM_FOR_WRAPAROUND  0x08    /* set by autovac only */
#define     PROC_IN_LOGICAL_DECODING    0x10    /* currently doing logical
                                                 * decoding outside xact */
#define     PROC_RESERVED               0x20    /* reserved for procarray */

/* flags reset at EOXact */
#define     PROC_VACUUM_STATE_MASK \
    (PROC_IN_VACUUM | PROC_VACUUM_FOR_WRAPAROUND)

/*
 * 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.
 */
#define     FP_LOCK_SLOTS_PER_BACKEND 16

/*
 * An invalid pgprocno.  Must be larger than the maximum number of PGPROC
 * structures we could possibly have.  See comments for MAX_BACKENDS.
 */
#define INVALID_PGPROCNO        PG_INT32_MAX

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.
 */
struct PGPROC
{
    /* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
    SHM_QUEUE   links;          /* list link if process is in a list */
    PGPROC    **procgloballist; /* procglobal list that owns this PGPROC */

    PGSemaphore sem;            /* ONE semaphore to sleep on */
    ProcWaitStatus waitStatus;

    Latch       procLatch;      /* generic latch for process */

    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         pgprocno;

    /* 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. */
    bool        lwWaiting;      /* true if waiting for an LW lock */
    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 */

    bool        delayChkpt;     /* true if this proc delays checkpoint start */

    /*
     * 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 */
    SHM_QUEUE   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.
     */
    SHM_QUEUE   myProcLocks[NUM_LOCK_PARTITIONS];

    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;
extern PGDLLIMPORT struct PGXACT *MyPgXact;

/*
 * Prior to PostgreSQL 9.2, the fields below were stored as part of the
 * PGPROC.  However, benchmarking revealed that packing these particular
 * members into a separate array as tightly as possible sped up GetSnapshotData
 * considerably on systems with many CPU cores, by reducing the number of
 * cache lines needing to be fetched.  Thus, think very carefully before adding
 * anything else here.
 */
typedef struct PGXACT
{
    TransactionId xid;          /* id of top-level transaction currently being
                                 * executed by this proc, if running and XID
                                 * is assigned; else InvalidTransactionId */

    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 ! */

    uint8       vacuumFlags;    /* vacuum-related flags, see above */
    bool        overflowed;

    uint8       nxids;
} PGXACT;

/*
 * There is one ProcGlobal struct for the whole database cluster.
 */
typedef struct PROC_HDR
{
    /* Array of PGPROC structures (not including dummies for prepared txns) */
    PGPROC     *allProcs;
    /* Array of PGXACT structures (not including dummies for prepared txns) */
    PGXACT     *allPgXact;
    /* Length of allProcs array */
    uint32      allProcCount;
    /* Head of list of free PGPROC structures */
    PGPROC     *freeProcs;
    /* Head of list of autovacuum's free PGPROC structures */
    PGPROC     *autovacFreeProcs;
    /* Head of list of bgworker free PGPROC structures */
    PGPROC     *bgworkerFreeProcs;
    /* Head of list of walsender free PGPROC structures */
    PGPROC     *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;
    /* The proc of the Startup process, since not in ProcArray */
    PGPROC     *startupProc;
    int         startupProcPid;
    /* Buffer id of the buffer that Startup process waits for pin on, or -1 */
    int         startupBufferPinWaitBufId;
} PROC_HDR;

extern PGDLLIMPORT PROC_HDR *ProcGlobal;

extern PGPROC *PreparedXactProcs;

/* Accessor for PGPROC given a pgprocno. */
#define GetPGProcByNumber(n) (&ProcGlobal->allProcs[(n)])

/*
 * 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 and WAL writer 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 4 slots.
 */
#define NUM_AUXILIARY_PROCS     4

/* configurable options */
extern PGDLLIMPORT int DeadlockTimeout;
extern PGDLLIMPORT int StatementTimeout;
extern PGDLLIMPORT int LockTimeout;
extern PGDLLIMPORT int IdleInTransactionSessionTimeout;
extern 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 PublishStartupProcessInformation(void);
extern void SetStartupBufferPinWaitBufId(int bufid);
extern int  GetStartupBufferPinWaitBufId(void);

extern bool HaveNFreeProcs(int n);
extern void ProcReleaseLocks(bool isCommit);

extern void ProcQueueInit(PROC_QUEUE *queue);
extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable);
extern PGPROC *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 pid);

extern PGPROC *AuxiliaryPidGetProc(int pid);

extern void BecomeLockGroupLeader(void);
extern bool BecomeLockGroupMember(PGPROC *leader, int pid);

#endif                          /* _PROC_H_ */