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db_include/storage/proc.h Executable file
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/*-------------------------------------------------------------------------
*
* proc.h
* per-process shared memory data structures
*
*
* Portions Copyright (c) 1996-2021, 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 */
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[]
*/
#define PROC_IS_AUTOVACUUM 0x01 /* is it an autovac worker? */
#define PROC_IN_VACUUM 0x02 /* currently running lazy vacuum */
#define PROC_IN_SAFE_IC 0x04 /* currently running CREATE INDEX
* CONCURRENTLY or REINDEX
* CONCURRENTLY on non-expressional,
* non-partial index */
#define PROC_VACUUM_FOR_WRAPAROUND 0x08 /* set by autovac only */
#define PROC_IN_LOGICAL_DECODING 0x10 /* currently doing logical
* decoding outside xact */
/* flags reset at EOXact */
#define PROC_VACUUM_STATE_MASK \
(PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
/*
* Flags that are valid to copy from another proc, the parallel leader
* process in practice. Currently, flags that are set during parallel
* vacuum and parallel index creation are allowed.
*/
#define PROC_COPYABLE_FLAGS (PROC_IN_VACUUM | PROC_IN_SAFE_IC)
/*
* 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.
*
* We allow many fields of this struct to be accessed without locks, such as
* delayChkpt 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) */
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 */
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;
/* 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 */
pg_atomic_uint64 waitStart; /* time at which wait for lock acquisition
* started */
bool delayChkpt; /* true if this proc delays checkpoint start */
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 */
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];
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 */
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, 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.
*/
#define NUM_AUXILIARY_PROCS 5
/* configurable options */
extern PGDLLIMPORT int DeadlockTimeout;
extern PGDLLIMPORT int StatementTimeout;
extern PGDLLIMPORT int LockTimeout;
extern PGDLLIMPORT int IdleInTransactionSessionTimeout;
extern PGDLLIMPORT int IdleSessionTimeout;
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_ */