mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-09-30 11:31:16 +02:00
008608b9d5
Previously we used a spinlock, in adition to the atomically manipulated
->state field, to protect the wait queue. But it's pretty simple to
instead perform the locking using a flag in state.
Due to 6150a1b0
BufferDescs, on platforms (like PPC) with > 1 byte
spinlocks, increased their size above 64byte. As 64 bytes are the size
we pad allocated BufferDescs to, this can increase false sharing;
causing performance problems in turn. Together with the previous commit
this reduces the size to <= 64 bytes on all common platforms.
Author: Andres Freund
Discussion: CAA4eK1+ZeB8PMwwktf+3bRS0Pt4Ux6Rs6Aom0uip8c6shJWmyg@mail.gmail.com
20160327121858.zrmrjegmji2ymnvr@alap3.anarazel.de
248 lines
9.2 KiB
C
248 lines
9.2 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* lwlock.h
|
|
* Lightweight lock manager
|
|
*
|
|
*
|
|
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
* src/include/storage/lwlock.h
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#ifndef LWLOCK_H
|
|
#define LWLOCK_H
|
|
|
|
#ifdef FRONTEND
|
|
#error "lwlock.h may not be included from frontend code"
|
|
#endif
|
|
|
|
#include "lib/ilist.h"
|
|
#include "storage/s_lock.h"
|
|
#include "port/atomics.h"
|
|
|
|
struct PGPROC;
|
|
|
|
/*
|
|
* Prior to PostgreSQL 9.4, every lightweight lock in the system was stored
|
|
* in a single array. For convenience and for compatibility with past
|
|
* releases, we still have a main array, but it's now also permissible to
|
|
* store LWLocks elsewhere in the main shared memory segment or in a dynamic
|
|
* shared memory segment. Each array of lwlocks forms a separate "tranche".
|
|
*
|
|
* It's occasionally necessary to identify a particular LWLock "by name"; e.g.
|
|
* because we wish to report the lock to dtrace. We could store a name or
|
|
* other identifying information in the lock itself, but since it's common
|
|
* to have many nearly-identical locks (e.g. one per buffer) this would end
|
|
* up wasting significant amounts of memory. Instead, each lwlock stores a
|
|
* tranche ID which tells us which array it's part of. Based on that, we can
|
|
* figure out where the lwlock lies within the array using the data structure
|
|
* shown below; the lock is then identified based on the tranche name and
|
|
* computed array index. We need the array stride because the array might not
|
|
* be an array of lwlocks, but rather some larger data structure that includes
|
|
* one or more lwlocks per element.
|
|
*/
|
|
typedef struct LWLockTranche
|
|
{
|
|
const char *name;
|
|
void *array_base;
|
|
Size array_stride;
|
|
} LWLockTranche;
|
|
|
|
/*
|
|
* Code outside of lwlock.c should not manipulate the contents of this
|
|
* structure directly, but we have to declare it here to allow LWLocks to be
|
|
* incorporated into other data structures.
|
|
*/
|
|
typedef struct LWLock
|
|
{
|
|
uint16 tranche; /* tranche ID */
|
|
pg_atomic_uint32 state; /* state of exclusive/nonexclusive lockers */
|
|
dlist_head waiters; /* list of waiting PGPROCs */
|
|
#ifdef LOCK_DEBUG
|
|
pg_atomic_uint32 nwaiters; /* number of waiters */
|
|
struct PGPROC *owner; /* last exclusive owner of the lock */
|
|
#endif
|
|
} LWLock;
|
|
|
|
/*
|
|
* In most cases, it's desirable to force each tranche of LWLocks to be aligned
|
|
* on a cache line boundary and make the array stride a power of 2. This saves
|
|
* a few cycles in indexing, but more importantly ensures that individual
|
|
* LWLocks don't cross cache line boundaries. This reduces cache contention
|
|
* problems, especially on AMD Opterons. In some cases, it's useful to add
|
|
* even more padding so that each LWLock takes up an entire cache line; this is
|
|
* useful, for example, in the main LWLock array, where the overall number of
|
|
* locks is small but some are heavily contended.
|
|
*
|
|
* When allocating a tranche that contains data other than LWLocks, it is
|
|
* probably best to include a bare LWLock and then pad the resulting structure
|
|
* as necessary for performance. For an array that contains only LWLocks,
|
|
* LWLockMinimallyPadded can be used for cases where we just want to ensure
|
|
* that we don't cross cache line boundaries within a single lock, while
|
|
* LWLockPadded can be used for cases where we want each lock to be an entire
|
|
* cache line.
|
|
*
|
|
* On 32-bit platforms, an LWLockMinimallyPadded might actually contain more
|
|
* than the absolute minimum amount of padding required to keep a lock from
|
|
* crossing a cache line boundary, because an unpadded LWLock might fit into
|
|
* 16 bytes. We ignore that possibility when determining the minimal amount
|
|
* of padding. Older releases had larger LWLocks, so 32 really was the
|
|
* minimum, and packing them in tighter might hurt performance.
|
|
*
|
|
* LWLOCK_MINIMAL_SIZE should be 32 on basically all common platforms, but
|
|
* because slock_t is more than 2 bytes on some obscure platforms, we allow
|
|
* for the possibility that it might be 64.
|
|
*/
|
|
#define LWLOCK_PADDED_SIZE PG_CACHE_LINE_SIZE
|
|
#define LWLOCK_MINIMAL_SIZE (sizeof(LWLock) <= 32 ? 32 : 64)
|
|
|
|
/* LWLock, padded to a full cache line size */
|
|
typedef union LWLockPadded
|
|
{
|
|
LWLock lock;
|
|
char pad[LWLOCK_PADDED_SIZE];
|
|
} LWLockPadded;
|
|
|
|
/* LWLock, minimally padded */
|
|
typedef union LWLockMinimallyPadded
|
|
{
|
|
LWLock lock;
|
|
char pad[LWLOCK_MINIMAL_SIZE];
|
|
} LWLockMinimallyPadded;
|
|
|
|
extern PGDLLIMPORT LWLockPadded *MainLWLockArray;
|
|
extern char *MainLWLockNames[];
|
|
|
|
/* struct for storing named tranche information */
|
|
typedef struct NamedLWLockTranche
|
|
{
|
|
LWLockTranche lwLockTranche;
|
|
int trancheId;
|
|
} NamedLWLockTranche;
|
|
|
|
extern PGDLLIMPORT NamedLWLockTranche *NamedLWLockTrancheArray;
|
|
extern PGDLLIMPORT int NamedLWLockTrancheRequests;
|
|
|
|
/* Names for fixed lwlocks */
|
|
#include "storage/lwlocknames.h"
|
|
|
|
/*
|
|
* It's a bit odd to declare NUM_BUFFER_PARTITIONS and NUM_LOCK_PARTITIONS
|
|
* here, but we need them to figure out offsets within MainLWLockArray, and
|
|
* having this file include lock.h or bufmgr.h would be backwards.
|
|
*/
|
|
|
|
/* Number of partitions of the shared buffer mapping hashtable */
|
|
#define NUM_BUFFER_PARTITIONS 128
|
|
|
|
/* Number of partitions the shared lock tables are divided into */
|
|
#define LOG2_NUM_LOCK_PARTITIONS 4
|
|
#define NUM_LOCK_PARTITIONS (1 << LOG2_NUM_LOCK_PARTITIONS)
|
|
|
|
/* Number of partitions the shared predicate lock tables are divided into */
|
|
#define LOG2_NUM_PREDICATELOCK_PARTITIONS 4
|
|
#define NUM_PREDICATELOCK_PARTITIONS (1 << LOG2_NUM_PREDICATELOCK_PARTITIONS)
|
|
|
|
/* Offsets for various chunks of preallocated lwlocks. */
|
|
#define BUFFER_MAPPING_LWLOCK_OFFSET NUM_INDIVIDUAL_LWLOCKS
|
|
#define LOCK_MANAGER_LWLOCK_OFFSET \
|
|
(BUFFER_MAPPING_LWLOCK_OFFSET + NUM_BUFFER_PARTITIONS)
|
|
#define PREDICATELOCK_MANAGER_LWLOCK_OFFSET \
|
|
(LOCK_MANAGER_LWLOCK_OFFSET + NUM_LOCK_PARTITIONS)
|
|
#define NUM_FIXED_LWLOCKS \
|
|
(PREDICATELOCK_MANAGER_LWLOCK_OFFSET + NUM_PREDICATELOCK_PARTITIONS)
|
|
|
|
typedef enum LWLockMode
|
|
{
|
|
LW_EXCLUSIVE,
|
|
LW_SHARED,
|
|
LW_WAIT_UNTIL_FREE /* A special mode used in PGPROC->lwlockMode,
|
|
* when waiting for lock to become free. Not
|
|
* to be used as LWLockAcquire argument */
|
|
} LWLockMode;
|
|
|
|
|
|
#ifdef LOCK_DEBUG
|
|
extern bool Trace_lwlocks;
|
|
#endif
|
|
|
|
extern bool LWLockAcquire(LWLock *lock, LWLockMode mode);
|
|
extern bool LWLockConditionalAcquire(LWLock *lock, LWLockMode mode);
|
|
extern bool LWLockAcquireOrWait(LWLock *lock, LWLockMode mode);
|
|
extern void LWLockRelease(LWLock *lock);
|
|
extern void LWLockReleaseClearVar(LWLock *lock, uint64 *valptr, uint64 val);
|
|
extern void LWLockReleaseAll(void);
|
|
extern bool LWLockHeldByMe(LWLock *lock);
|
|
|
|
extern bool LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval);
|
|
extern void LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 value);
|
|
|
|
extern Size LWLockShmemSize(void);
|
|
extern void CreateLWLocks(void);
|
|
extern void InitLWLockAccess(void);
|
|
|
|
extern const char *GetLWLockIdentifier(uint8 classId, uint16 eventId);
|
|
|
|
/*
|
|
* Extensions (or core code) can obtain an LWLocks by calling
|
|
* RequestNamedLWLockTranche() during postmaster startup. Subsequently,
|
|
* call GetNamedLWLockTranche() to obtain a pointer to an array containing
|
|
* the number of LWLocks requested.
|
|
*/
|
|
extern void RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks);
|
|
extern LWLockPadded *GetNamedLWLockTranche(const char *tranche_name);
|
|
|
|
/*
|
|
* There is another, more flexible method of obtaining lwlocks. First, call
|
|
* LWLockNewTrancheId just once to obtain a tranche ID; this allocates from
|
|
* a shared counter. Next, each individual process using the tranche should
|
|
* call LWLockRegisterTranche() to associate that tranche ID with appropriate
|
|
* metadata. Finally, LWLockInitialize should be called just once per lwlock,
|
|
* passing the tranche ID as an argument.
|
|
*
|
|
* It may seem strange that each process using the tranche must register it
|
|
* separately, but dynamic shared memory segments aren't guaranteed to be
|
|
* mapped at the same address in all coordinating backends, so storing the
|
|
* registration in the main shared memory segment wouldn't work for that case.
|
|
*/
|
|
extern int LWLockNewTrancheId(void);
|
|
extern void LWLockRegisterTranche(int tranche_id, LWLockTranche *tranche);
|
|
extern void LWLockInitialize(LWLock *lock, int tranche_id);
|
|
|
|
/*
|
|
* We reserve a few predefined tranche IDs. A call to LWLockNewTrancheId
|
|
* will never return a value less than LWTRANCHE_FIRST_USER_DEFINED.
|
|
*/
|
|
typedef enum BuiltinTrancheIds
|
|
{
|
|
LWTRANCHE_MAIN,
|
|
LWTRANCHE_CLOG_BUFFERS,
|
|
LWTRANCHE_COMMITTS_BUFFERS,
|
|
LWTRANCHE_SUBTRANS_BUFFERS,
|
|
LWTRANCHE_MXACTOFFSET_BUFFERS,
|
|
LWTRANCHE_MXACTMEMBER_BUFFERS,
|
|
LWTRANCHE_ASYNC_BUFFERS,
|
|
LWTRANCHE_OLDSERXID_BUFFERS,
|
|
LWTRANCHE_WAL_INSERT,
|
|
LWTRANCHE_BUFFER_CONTENT,
|
|
LWTRANCHE_BUFFER_IO_IN_PROGRESS,
|
|
LWTRANCHE_REPLICATION_ORIGIN,
|
|
LWTRANCHE_REPLICATION_SLOT_IO_IN_PROGRESS,
|
|
LWTRANCHE_PROC,
|
|
LWTRANCHE_BUFFER_MAPPING,
|
|
LWTRANCHE_LOCK_MANAGER,
|
|
LWTRANCHE_PREDICATE_LOCK_MANAGER,
|
|
LWTRANCHE_FIRST_USER_DEFINED
|
|
} BuiltinTrancheIds;
|
|
|
|
/*
|
|
* Prior to PostgreSQL 9.4, we used an enum type called LWLockId to refer
|
|
* to LWLocks. New code should instead use LWLock *. However, for the
|
|
* convenience of third-party code, we include the following typedef.
|
|
*/
|
|
typedef LWLock *LWLockId;
|
|
|
|
#endif /* LWLOCK_H */
|