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proc.h
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1 /*-------------------------------------------------------------------------
2  *
3  * proc.h
4  * per-process shared memory data structures
5  *
6  *
7  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
8  * Portions Copyright (c) 1994, Regents of the University of California
9  *
10  * src/include/storage/proc.h
11  *
12  *-------------------------------------------------------------------------
13  */
14 #ifndef _PROC_H_
15 #define _PROC_H_
16 
17 #include "access/clog.h"
18 #include "access/xlogdefs.h"
19 #include "lib/ilist.h"
20 #include "storage/latch.h"
21 #include "storage/lock.h"
22 #include "storage/pg_sema.h"
23 #include "storage/proclist_types.h"
24 
25 /*
26  * Each backend advertises up to PGPROC_MAX_CACHED_SUBXIDS TransactionIds
27  * for non-aborted subtransactions of its current top transaction. These
28  * have to be treated as running XIDs by other backends.
29  *
30  * We also keep track of whether the cache overflowed (ie, the transaction has
31  * generated at least one subtransaction that didn't fit in the cache).
32  * If none of the caches have overflowed, we can assume that an XID that's not
33  * listed anywhere in the PGPROC array is not a running transaction. Else we
34  * have to look at pg_subtrans.
35  */
36 #define PGPROC_MAX_CACHED_SUBXIDS 64 /* XXX guessed-at value */
37 
38 typedef struct XidCacheStatus
39 {
40  /* number of cached subxids, never more than PGPROC_MAX_CACHED_SUBXIDS */
42  /* has PGPROC->subxids overflowed */
43  bool overflowed;
45 
46 struct XidCache
47 {
49 };
50 
51 /*
52  * Flags for PGPROC->statusFlags and PROC_HDR->statusFlags[]
53  */
54 #define PROC_IS_AUTOVACUUM 0x01 /* is it an autovac worker? */
55 #define PROC_IN_VACUUM 0x02 /* currently running lazy vacuum */
56 #define PROC_IN_SAFE_IC 0x04 /* currently running CREATE INDEX
57  * CONCURRENTLY or REINDEX
58  * CONCURRENTLY on non-expressional,
59  * non-partial index */
60 #define PROC_VACUUM_FOR_WRAPAROUND 0x08 /* set by autovac only */
61 #define PROC_IN_LOGICAL_DECODING 0x10 /* currently doing logical
62  * decoding outside xact */
63 
64 /* flags reset at EOXact */
65 #define PROC_VACUUM_STATE_MASK \
66  (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND)
67 
68 /*
69  * We allow a small number of "weak" relation locks (AccessShareLock,
70  * RowShareLock, RowExclusiveLock) to be recorded in the PGPROC structure
71  * rather than the main lock table. This eases contention on the lock
72  * manager LWLocks. See storage/lmgr/README for additional details.
73  */
74 #define FP_LOCK_SLOTS_PER_BACKEND 16
75 
76 /*
77  * An invalid pgprocno. Must be larger than the maximum number of PGPROC
78  * structures we could possibly have. See comments for MAX_BACKENDS.
79  */
80 #define INVALID_PGPROCNO PG_INT32_MAX
81 
82 typedef enum
83 {
88 
89 /*
90  * Each backend has a PGPROC struct in shared memory. There is also a list of
91  * currently-unused PGPROC structs that will be reallocated to new backends.
92  *
93  * links: list link for any list the PGPROC is in. When waiting for a lock,
94  * the PGPROC is linked into that lock's waitProcs queue. A recycled PGPROC
95  * is linked into ProcGlobal's freeProcs list.
96  *
97  * Note: twophase.c also sets up a dummy PGPROC struct for each currently
98  * prepared transaction. These PGPROCs appear in the ProcArray data structure
99  * so that the prepared transactions appear to be still running and are
100  * correctly shown as holding locks. A prepared transaction PGPROC can be
101  * distinguished from a real one at need by the fact that it has pid == 0.
102  * The semaphore and lock-activity fields in a prepared-xact PGPROC are unused,
103  * but its myProcLocks[] lists are valid.
104  *
105  * We allow many fields of this struct to be accessed without locks, such as
106  * delayChkpt and isBackgroundWorker. However, keep in mind that writing
107  * mirrored ones (see below) requires holding ProcArrayLock or XidGenLock in
108  * at least shared mode, so that pgxactoff does not change concurrently.
109  *
110  * Mirrored fields:
111  *
112  * Some fields in PGPROC (see "mirrored in ..." comment) are mirrored into an
113  * element of more densely packed ProcGlobal arrays. These arrays are indexed
114  * by PGPROC->pgxactoff. Both copies need to be maintained coherently.
115  *
116  * NB: The pgxactoff indexed value can *never* be accessed without holding
117  * locks.
118  *
119  * See PROC_HDR for details.
120  */
121 struct PGPROC
122 {
123  /* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
124  SHM_QUEUE links; /* list link if process is in a list */
125  PGPROC **procgloballist; /* procglobal list that owns this PGPROC */
126 
127  PGSemaphore sem; /* ONE semaphore to sleep on */
129 
130  Latch procLatch; /* generic latch for process */
131 
132 
133  TransactionId xid; /* id of top-level transaction currently being
134  * executed by this proc, if running and XID
135  * is assigned; else InvalidTransactionId.
136  * mirrored in ProcGlobal->xids[pgxactoff] */
137 
138  TransactionId xmin; /* minimal running XID as it was when we were
139  * starting our xact, excluding LAZY VACUUM:
140  * vacuum must not remove tuples deleted by
141  * xid >= xmin ! */
142 
143  LocalTransactionId lxid; /* local id of top-level transaction currently
144  * being executed by this proc, if running;
145  * else InvalidLocalTransactionId */
146  int pid; /* Backend's process ID; 0 if prepared xact */
147 
148  int pgxactoff; /* offset into various ProcGlobal->arrays
149  * with data mirrored from this PGPROC */
150  int pgprocno;
151 
152  /* These fields are zero while a backend is still starting up: */
153  BackendId backendId; /* This backend's backend ID (if assigned) */
154  Oid databaseId; /* OID of database this backend is using */
155  Oid roleId; /* OID of role using this backend */
156 
157  Oid tempNamespaceId; /* OID of temp schema this backend is
158  * using */
159 
160  bool isBackgroundWorker; /* true if background worker. */
161 
162  /*
163  * While in hot standby mode, shows that a conflict signal has been sent
164  * for the current transaction. Set/cleared while holding ProcArrayLock,
165  * though not required. Accessed without lock, if needed.
166  */
168 
169  /* Info about LWLock the process is currently waiting for, if any. */
170  bool lwWaiting; /* true if waiting for an LW lock */
171  uint8 lwWaitMode; /* lwlock mode being waited for */
172  proclist_node lwWaitLink; /* position in LW lock wait list */
173 
174  /* Support for condition variables. */
175  proclist_node cvWaitLink; /* position in CV wait list */
176 
177  /* Info about lock the process is currently waiting for, if any. */
178  /* waitLock and waitProcLock are NULL if not currently waiting. */
179  LOCK *waitLock; /* Lock object we're sleeping on ... */
180  PROCLOCK *waitProcLock; /* Per-holder info for awaited lock */
181  LOCKMODE waitLockMode; /* type of lock we're waiting for */
182  LOCKMASK heldLocks; /* bitmask for lock types already held on this
183  * lock object by this backend */
184 
185  bool delayChkpt; /* true if this proc delays checkpoint start */
186 
187  uint8 statusFlags; /* this backend's status flags, see PROC_*
188  * above. mirrored in
189  * ProcGlobal->statusFlags[pgxactoff] */
190 
191  /*
192  * Info to allow us to wait for synchronous replication, if needed.
193  * waitLSN is InvalidXLogRecPtr if not waiting; set only by user backend.
194  * syncRepState must not be touched except by owning process or WALSender.
195  * syncRepLinks used only while holding SyncRepLock.
196  */
197  XLogRecPtr waitLSN; /* waiting for this LSN or higher */
198  int syncRepState; /* wait state for sync rep */
199  SHM_QUEUE syncRepLinks; /* list link if process is in syncrep queue */
200 
201  /*
202  * All PROCLOCK objects for locks held or awaited by this backend are
203  * linked into one of these lists, according to the partition number of
204  * their lock.
205  */
207 
208  XidCacheStatus subxidStatus; /* mirrored with
209  * ProcGlobal->subxidStates[i] */
210  struct XidCache subxids; /* cache for subtransaction XIDs */
211 
212  /* Support for group XID clearing. */
213  /* true, if member of ProcArray group waiting for XID clear */
215  /* next ProcArray group member waiting for XID clear */
217 
218  /*
219  * latest transaction id among the transaction's main XID and
220  * subtransactions
221  */
223 
224  uint32 wait_event_info; /* proc's wait information */
225 
226  /* Support for group transaction status update. */
227  bool clogGroupMember; /* true, if member of clog group */
228  pg_atomic_uint32 clogGroupNext; /* next clog group member */
229  TransactionId clogGroupMemberXid; /* transaction id of clog group member */
230  XidStatus clogGroupMemberXidStatus; /* transaction status of clog
231  * group member */
232  int clogGroupMemberPage; /* clog page corresponding to
233  * transaction id of clog group member */
234  XLogRecPtr clogGroupMemberLsn; /* WAL location of commit record for clog
235  * group member */
236 
237  /* Lock manager data, recording fast-path locks taken by this backend. */
238  LWLock fpInfoLock; /* protects per-backend fast-path state */
239  uint64 fpLockBits; /* lock modes held for each fast-path slot */
240  Oid fpRelId[FP_LOCK_SLOTS_PER_BACKEND]; /* slots for rel oids */
241  bool fpVXIDLock; /* are we holding a fast-path VXID lock? */
242  LocalTransactionId fpLocalTransactionId; /* lxid for fast-path VXID
243  * lock */
244 
245  /*
246  * Support for lock groups. Use LockHashPartitionLockByProc on the group
247  * leader to get the LWLock protecting these fields.
248  */
249  PGPROC *lockGroupLeader; /* lock group leader, if I'm a member */
250  dlist_head lockGroupMembers; /* list of members, if I'm a leader */
251  dlist_node lockGroupLink; /* my member link, if I'm a member */
252 };
253 
254 /* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */
255 
256 
257 extern PGDLLIMPORT PGPROC *MyProc;
258 
259 /*
260  * There is one ProcGlobal struct for the whole database cluster.
261  *
262  * Adding/Removing an entry into the procarray requires holding *both*
263  * ProcArrayLock and XidGenLock in exclusive mode (in that order). Both are
264  * needed because the dense arrays (see below) are accessed from
265  * GetNewTransactionId() and GetSnapshotData(), and we don't want to add
266  * further contention by both using the same lock. Adding/Removing a procarray
267  * entry is much less frequent.
268  *
269  * Some fields in PGPROC are mirrored into more densely packed arrays (e.g.
270  * xids), with one entry for each backend. These arrays only contain entries
271  * for PGPROCs that have been added to the shared array with ProcArrayAdd()
272  * (in contrast to PGPROC array which has unused PGPROCs interspersed).
273  *
274  * The dense arrays are indexed by PGPROC->pgxactoff. Any concurrent
275  * ProcArrayAdd() / ProcArrayRemove() can lead to pgxactoff of a procarray
276  * member to change. Therefore it is only safe to use PGPROC->pgxactoff to
277  * access the dense array while holding either ProcArrayLock or XidGenLock.
278  *
279  * As long as a PGPROC is in the procarray, the mirrored values need to be
280  * maintained in both places in a coherent manner.
281  *
282  * The denser separate arrays are beneficial for three main reasons: First, to
283  * allow for as tight loops accessing the data as possible. Second, to prevent
284  * updates of frequently changing data (e.g. xmin) from invalidating
285  * cachelines also containing less frequently changing data (e.g. xid,
286  * statusFlags). Third to condense frequently accessed data into as few
287  * cachelines as possible.
288  *
289  * There are two main reasons to have the data mirrored between these dense
290  * arrays and PGPROC. First, as explained above, a PGPROC's array entries can
291  * only be accessed with either ProcArrayLock or XidGenLock held, whereas the
292  * PGPROC entries do not require that (obviously there may still be locking
293  * requirements around the individual field, separate from the concerns
294  * here). That is particularly important for a backend to efficiently checks
295  * it own values, which it often can safely do without locking. Second, the
296  * PGPROC fields allow to avoid unnecessary accesses and modification to the
297  * dense arrays. A backend's own PGPROC is more likely to be in a local cache,
298  * whereas the cachelines for the dense array will be modified by other
299  * backends (often removing it from the cache for other cores/sockets). At
300  * commit/abort time a check of the PGPROC value can avoid accessing/dirtying
301  * the corresponding array value.
302  *
303  * Basically it makes sense to access the PGPROC variable when checking a
304  * single backend's data, especially when already looking at the PGPROC for
305  * other reasons already. It makes sense to look at the "dense" arrays if we
306  * need to look at many / most entries, because we then benefit from the
307  * reduced indirection and better cross-process cache-ability.
308  *
309  * When entering a PGPROC for 2PC transactions with ProcArrayAdd(), the data
310  * in the dense arrays is initialized from the PGPROC while it already holds
311  * ProcArrayLock.
312  */
313 typedef struct PROC_HDR
314 {
315  /* Array of PGPROC structures (not including dummies for prepared txns) */
317 
318  /* Array mirroring PGPROC.xid for each PGPROC currently in the procarray */
320 
321  /*
322  * Array mirroring PGPROC.subxidStatus for each PGPROC currently in the
323  * procarray.
324  */
326 
327  /*
328  * Array mirroring PGPROC.statusFlags for each PGPROC currently in the
329  * procarray.
330  */
332 
333  /* Length of allProcs array */
335  /* Head of list of free PGPROC structures */
337  /* Head of list of autovacuum's free PGPROC structures */
339  /* Head of list of bgworker free PGPROC structures */
341  /* Head of list of walsender free PGPROC structures */
343  /* First pgproc waiting for group XID clear */
345  /* First pgproc waiting for group transaction status update */
347  /* WALWriter process's latch */
349  /* Checkpointer process's latch */
351  /* Current shared estimate of appropriate spins_per_delay value */
353  /* The proc of the Startup process, since not in ProcArray */
356  /* Buffer id of the buffer that Startup process waits for pin on, or -1 */
358 } PROC_HDR;
359 
361 
362 extern PGPROC *PreparedXactProcs;
363 
364 /* Accessor for PGPROC given a pgprocno. */
365 #define GetPGProcByNumber(n) (&ProcGlobal->allProcs[(n)])
366 
367 /*
368  * We set aside some extra PGPROC structures for auxiliary processes,
369  * ie things that aren't full-fledged backends but need shmem access.
370  *
371  * Background writer, checkpointer and WAL writer run during normal operation.
372  * Startup process and WAL receiver also consume 2 slots, but WAL writer is
373  * launched only after startup has exited, so we only need 4 slots.
374  */
375 #define NUM_AUXILIARY_PROCS 4
376 
377 /* configurable options */
378 extern PGDLLIMPORT int DeadlockTimeout;
379 extern PGDLLIMPORT int StatementTimeout;
380 extern PGDLLIMPORT int LockTimeout;
383 extern bool log_lock_waits;
384 
385 
386 /*
387  * Function Prototypes
388  */
389 extern int ProcGlobalSemas(void);
390 extern Size ProcGlobalShmemSize(void);
391 extern void InitProcGlobal(void);
392 extern void InitProcess(void);
393 extern void InitProcessPhase2(void);
394 extern void InitAuxiliaryProcess(void);
395 
396 extern void PublishStartupProcessInformation(void);
397 extern void SetStartupBufferPinWaitBufId(int bufid);
398 extern int GetStartupBufferPinWaitBufId(void);
399 
400 extern bool HaveNFreeProcs(int n);
401 extern void ProcReleaseLocks(bool isCommit);
402 
403 extern void ProcQueueInit(PROC_QUEUE *queue);
404 extern ProcWaitStatus ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable);
405 extern PGPROC *ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus);
406 extern void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock);
407 extern void CheckDeadLockAlert(void);
408 extern bool IsWaitingForLock(void);
409 extern void LockErrorCleanup(void);
410 
411 extern void ProcWaitForSignal(uint32 wait_event_info);
412 extern void ProcSendSignal(int pid);
413 
414 extern PGPROC *AuxiliaryPidGetProc(int pid);
415 
416 extern void BecomeLockGroupLeader(void);
417 extern bool BecomeLockGroupMember(PGPROC *leader, int pid);
418 
419 #endif /* _PROC_H_ */
PGDLLIMPORT PGPROC * MyProc
Definition: proc.c:68
bool procArrayGroupMember
Definition: proc.h:214
Definition: lwlock.h:31
XidStatus clogGroupMemberXidStatus
Definition: proc.h:230
bool log_lock_waits
Definition: proc.c:65
PGDLLIMPORT int StatementTimeout
Definition: proc.c:61
BackendId backendId
Definition: proc.h:153
uint32 TransactionId
Definition: c.h:575
uint32 wait_event_info
Definition: proc.h:224
int LOCKMODE
Definition: lockdefs.h:26
XLogRecPtr clogGroupMemberLsn
Definition: proc.h:234
dlist_head lockGroupMembers
Definition: proc.h:250
XidCacheStatus * subxidStates
Definition: proc.h:325
Oid tempNamespaceId
Definition: proc.h:157
SHM_QUEUE links
Definition: proc.h:124
LOCKMODE waitLockMode
Definition: proc.h:181
bool lwWaiting
Definition: proc.h:170
unsigned char uint8
Definition: c.h:427
PGDLLIMPORT int LockTimeout
Definition: proc.c:62
int XidStatus
Definition: clog.h:25
PGPROC * bgworkerFreeProcs
Definition: proc.h:340
int GetStartupBufferPinWaitBufId(void)
Definition: proc.c:653
Oid roleId
Definition: proc.h:155
void LockErrorCleanup(void)
Definition: proc.c:707
uint8 statusFlags
Definition: proc.h:187
uint8 lwWaitMode
Definition: proc.h:171
pg_atomic_uint32 clogGroupNext
Definition: proc.h:228
ProcWaitStatus waitStatus
Definition: proc.h:128
bool fpVXIDLock
Definition: proc.h:241
unsigned int Oid
Definition: postgres_ext.h:31
PGPROC * autovacFreeProcs
Definition: proc.h:338
void ProcSendSignal(int pid)
Definition: proc.c:1879
XidCacheStatus subxidStatus
Definition: proc.h:208
PGPROC * walsenderFreeProcs
Definition: proc.h:342
void SetStartupBufferPinWaitBufId(int bufid)
Definition: proc.c:641
Latch procLatch
Definition: proc.h:130
void InitProcessPhase2(void)
Definition: proc.c:477
#define PGDLLIMPORT
Definition: c.h:1305
PGPROC * AuxiliaryPidGetProc(int pid)
Definition: proc.c:981
bool overflowed
Definition: proc.h:43
PGDLLIMPORT int DeadlockTimeout
Definition: proc.c:60
bool isBackgroundWorker
Definition: proc.h:160
PGDLLIMPORT int IdleInTransactionSessionTimeout
Definition: proc.c:63
dlist_node lockGroupLink
Definition: proc.h:251
Latch * walwriterLatch
Definition: proc.h:348
int spins_per_delay
Definition: proc.h:352
bool delayChkpt
Definition: proc.h:185
bool BecomeLockGroupMember(PGPROC *leader, int pid)
Definition: proc.c:1947
int ProcGlobalSemas(void)
Definition: proc.c:124
proclist_node lwWaitLink
Definition: proc.h:172
TransactionId xmin
Definition: proc.h:138
void ProcWaitForSignal(uint32 wait_event_info)
Definition: proc.c:1867
PROCLOCK * waitProcLock
Definition: proc.h:180
Definition: latch.h:110
int clogGroupMemberPage
Definition: proc.h:232
#define FP_LOCK_SLOTS_PER_BACKEND
Definition: proc.h:74
bool recoveryConflictPending
Definition: proc.h:167
bool HaveNFreeProcs(int n)
Definition: proc.c:667
TransactionId * xids
Definition: proc.h:319
TransactionId clogGroupMemberXid
Definition: proc.h:229
Oid databaseId
Definition: proc.h:154
unsigned int uint32
Definition: c.h:429
PGPROC ** procgloballist
Definition: proc.h:125
Definition: lock.h:297
uint32 LocalTransactionId
Definition: c.h:577
LOCK * waitLock
Definition: proc.h:179
void ProcReleaseLocks(bool isCommit)
Definition: proc.c:783
PGDLLIMPORT int IdleSessionTimeout
Definition: proc.c:64
void BecomeLockGroupLeader(void)
Definition: proc.c:1917
void ProcLockWakeup(LockMethod lockMethodTable, LOCK *lock)
Definition: proc.c:1696
pg_atomic_uint32 procArrayGroupNext
Definition: proc.h:216
Definition: proc.h:313
PGPROC * PreparedXactProcs
Definition: proc.c:82
int startupProcPid
Definition: proc.h:355
uint64 fpLockBits
Definition: proc.h:239
struct XidCacheStatus XidCacheStatus
int BackendId
Definition: backendid.h:21
PGPROC * ProcWakeup(PGPROC *proc, ProcWaitStatus waitStatus)
Definition: proc.c:1660
ProcWaitStatus
Definition: proc.h:82
#define PGPROC_MAX_CACHED_SUBXIDS
Definition: proc.h:36
ProcWaitStatus ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
Definition: proc.c:1058
Latch * checkpointerLatch
Definition: proc.h:350
PGDLLIMPORT PROC_HDR * ProcGlobal
Definition: proc.c:80
void InitProcGlobal(void)
Definition: proc.c:159
void ProcQueueInit(PROC_QUEUE *queue)
Definition: proc.c:1034
uint64 XLogRecPtr
Definition: xlogdefs.h:21
void CheckDeadLockAlert(void)
Definition: proc.c:1841
PGPROC * freeProcs
Definition: proc.h:336
void InitAuxiliaryProcess(void)
Definition: proc.c:512
size_t Size
Definition: c.h:528
SHM_QUEUE syncRepLinks
Definition: proc.h:199
uint32 allProcCount
Definition: proc.h:334
int LOCKMASK
Definition: lockdefs.h:25
proclist_node cvWaitLink
Definition: proc.h:175
uint8 count
Definition: proc.h:41
TransactionId xid
Definition: proc.h:133
pg_atomic_uint32 clogGroupFirst
Definition: proc.h:346
void PublishStartupProcessInformation(void)
Definition: proc.c:623
Definition: lock.h:358
int pgprocno
Definition: proc.h:150
pg_atomic_uint32 procArrayGroupFirst
Definition: proc.h:344
bool IsWaitingForLock(void)
Definition: proc.c:690
bool clogGroupMember
Definition: proc.h:227
int startupBufferPinWaitBufId
Definition: proc.h:357
int pgxactoff
Definition: proc.h:148
void InitProcess(void)
Definition: proc.c:302
PGPROC * allProcs
Definition: proc.h:316
struct PROC_HDR PROC_HDR
PGPROC * startupProc
Definition: proc.h:354
LWLock fpInfoLock
Definition: proc.h:238
uint8 * statusFlags
Definition: proc.h:331
PGSemaphore sem
Definition: proc.h:127
int syncRepState
Definition: proc.h:198
Definition: proc.h:121
int pid
Definition: proc.h:146
Size ProcGlobalShmemSize(void)
Definition: proc.c:102
XLogRecPtr waitLSN
Definition: proc.h:197
PGPROC * lockGroupLeader
Definition: proc.h:249
LocalTransactionId fpLocalTransactionId
Definition: proc.h:242
TransactionId procArrayGroupMemberXid
Definition: proc.h:222
LOCKMASK heldLocks
Definition: proc.h:182
#define NUM_LOCK_PARTITIONS
Definition: lwlock.h:115
Definition: proc.h:46
LocalTransactionId lxid
Definition: proc.h:143