295e63983d
rows will normally never obtain an XID at all. We already did things this way for subtransactions, but this patch extends the concept to top-level transactions. In applications where there are lots of short read-only transactions, this should improve performance noticeably; not so much from removal of the actual XID-assignments, as from reduction of overhead that's driven by the rate of XID consumption. We add a concept of a "virtual transaction ID" so that active transactions can be uniquely identified even if they don't have a regular XID. This is a much lighter-weight concept: uniqueness of VXIDs is only guaranteed over the short term, and no on-disk record is made about them. Florian Pflug, with some editorialization by Tom.
171 lines
5.9 KiB
C
171 lines
5.9 KiB
C
/*-------------------------------------------------------------------------
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*
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* proc.h
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* per-process shared memory data structures
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*
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*
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/storage/proc.h,v 1.100 2007/09/05 18:10:48 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef _PROC_H_
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#define _PROC_H_
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#include "storage/lock.h"
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#include "storage/pg_sema.h"
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/*
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* Each backend advertises up to PGPROC_MAX_CACHED_SUBXIDS TransactionIds
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* for non-aborted subtransactions of its current top transaction. These
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* have to be treated as running XIDs by other backends.
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*
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* We also keep track of whether the cache overflowed (ie, the transaction has
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* generated at least one subtransaction that didn't fit in the cache).
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* If none of the caches have overflowed, we can assume that an XID that's not
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* listed anywhere in the PGPROC array is not a running transaction. Else we
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* have to look at pg_subtrans.
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*/
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#define PGPROC_MAX_CACHED_SUBXIDS 64 /* XXX guessed-at value */
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struct XidCache
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{
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bool overflowed;
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int nxids;
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TransactionId xids[PGPROC_MAX_CACHED_SUBXIDS];
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};
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/*
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* Each backend has a PGPROC struct in shared memory. There is also a list of
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* currently-unused PGPROC structs that will be reallocated to new backends.
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*
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* links: list link for any list the PGPROC is in. When waiting for a lock,
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* the PGPROC is linked into that lock's waitProcs queue. A recycled PGPROC
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* is linked into ProcGlobal's freeProcs list.
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*
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* Note: twophase.c also sets up a dummy PGPROC struct for each currently
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* prepared transaction. These PGPROCs appear in the ProcArray data structure
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* so that the prepared transactions appear to be still running and are
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* correctly shown as holding locks. A prepared transaction PGPROC can be
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* distinguished from a real one at need by the fact that it has pid == 0.
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* The semaphore and lock-activity fields in a prepared-xact PGPROC are unused,
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* but its myProcLocks[] lists are valid.
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*/
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struct PGPROC
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{
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/* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
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SHM_QUEUE links; /* list link if process is in a list */
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PGSemaphoreData sem; /* ONE semaphore to sleep on */
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int waitStatus; /* STATUS_WAITING, STATUS_OK or STATUS_ERROR */
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LocalTransactionId lxid; /* local id of top-level transaction currently
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* being executed by this proc, if running;
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* else InvalidLocalTransactionId */
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TransactionId xid; /* id of top-level transaction currently being
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* executed by this proc, if running and XID
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* is assigned; else InvalidTransactionId */
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TransactionId xmin; /* minimal running XID as it was when we were
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* starting our xact, excluding LAZY VACUUM:
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* vacuum must not remove tuples deleted by
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* xid >= xmin ! */
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int pid; /* This backend's process id, or 0 */
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BackendId backendId; /* This backend's backend ID (if assigned) */
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Oid databaseId; /* OID of database this backend is using */
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Oid roleId; /* OID of role using this backend */
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bool inCommit; /* true if within commit critical section */
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bool inVacuum; /* true if current xact is a LAZY VACUUM */
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bool isAutovacuum; /* true if it's autovacuum */
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/* Info about LWLock the process is currently waiting for, if any. */
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bool lwWaiting; /* true if waiting for an LW lock */
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bool lwExclusive; /* true if waiting for exclusive access */
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struct PGPROC *lwWaitLink; /* next waiter for same LW lock */
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/* Info about lock the process is currently waiting for, if any. */
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/* waitLock and waitProcLock are NULL if not currently waiting. */
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LOCK *waitLock; /* Lock object we're sleeping on ... */
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PROCLOCK *waitProcLock; /* Per-holder info for awaited lock */
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LOCKMODE waitLockMode; /* type of lock we're waiting for */
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LOCKMASK heldLocks; /* bitmask for lock types already held on this
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* lock object by this backend */
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/*
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* All PROCLOCK objects for locks held or awaited by this backend are
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* linked into one of these lists, according to the partition number of
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* their lock.
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*/
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SHM_QUEUE myProcLocks[NUM_LOCK_PARTITIONS];
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struct XidCache subxids; /* cache for subtransaction XIDs */
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};
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/* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */
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extern PGDLLIMPORT PGPROC *MyProc;
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/*
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* There is one ProcGlobal struct for the whole database cluster.
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*/
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typedef struct PROC_HDR
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{
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/* Head of list of free PGPROC structures */
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SHMEM_OFFSET freeProcs;
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/* Head of list of autovacuum's free PGPROC structures */
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SHMEM_OFFSET autovacFreeProcs;
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/* Current shared estimate of appropriate spins_per_delay value */
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int spins_per_delay;
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} PROC_HDR;
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/*
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* We set aside some extra PGPROC structures for auxiliary processes,
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* ie things that aren't full-fledged backends but need shmem access.
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*/
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#define NUM_AUXILIARY_PROCS 3
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/* configurable options */
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extern int DeadlockTimeout;
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extern int StatementTimeout;
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extern bool log_lock_waits;
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extern volatile bool cancel_from_timeout;
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/*
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* Function Prototypes
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*/
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extern int ProcGlobalSemas(void);
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extern Size ProcGlobalShmemSize(void);
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extern void InitProcGlobal(void);
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extern void InitProcess(void);
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extern void InitProcessPhase2(void);
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extern void InitAuxiliaryProcess(void);
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extern bool HaveNFreeProcs(int n);
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extern void ProcReleaseLocks(bool isCommit);
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extern void ProcQueueInit(PROC_QUEUE *queue);
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extern int ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable);
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extern PGPROC *ProcWakeup(PGPROC *proc, int waitStatus);
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extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock);
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extern bool LockWaitCancel(void);
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extern void ProcWaitForSignal(void);
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extern void ProcSendSignal(int pid);
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extern bool enable_sig_alarm(int delayms, bool is_statement_timeout);
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extern bool disable_sig_alarm(bool is_statement_timeout);
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extern void handle_sig_alarm(SIGNAL_ARGS);
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#endif /* PROC_H */
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