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xid8funcs.c File Reference
#include "postgres.h"
#include "access/transam.h"
#include "access/xact.h"
#include "funcapi.h"
#include "lib/qunique.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "postmaster/postmaster.h"
#include "storage/lwlock.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
#include "utils/memutils.h"
#include "utils/snapmgr.h"
#include "utils/xid8.h"
Include dependency graph for xid8funcs.c:

Go to the source code of this file.

Data Structures

struct  pg_snapshot
 

Macros

#define USE_BSEARCH_IF_NXIP_GREATER   30
 
#define PG_SNAPSHOT_SIZE(nxip)    (offsetof(pg_snapshot, xip) + sizeof(FullTransactionId) * (nxip))
 
#define PG_SNAPSHOT_MAX_NXIP    ((MaxAllocSize - offsetof(pg_snapshot, xip)) / sizeof(FullTransactionId))
 

Functions

 StaticAssertDecl (MAX_BACKENDS *2<=PG_SNAPSHOT_MAX_NXIP, "possible overflow in pg_current_snapshot()")
 
static bool TransactionIdInRecentPast (FullTransactionId fxid, TransactionId *extracted_xid)
 
static FullTransactionId widen_snapshot_xid (TransactionId xid, FullTransactionId next_fxid)
 
static int cmp_fxid (const void *aa, const void *bb)
 
static void sort_snapshot (pg_snapshot *snap)
 
static bool is_visible_fxid (FullTransactionId value, const pg_snapshot *snap)
 
static StringInfo buf_init (FullTransactionId xmin, FullTransactionId xmax)
 
static void buf_add_txid (StringInfo buf, FullTransactionId fxid)
 
static pg_snapshotbuf_finalize (StringInfo buf)
 
static pg_snapshotparse_snapshot (const char *str, Node *escontext)
 
Datum pg_current_xact_id (PG_FUNCTION_ARGS)
 
Datum pg_current_xact_id_if_assigned (PG_FUNCTION_ARGS)
 
Datum pg_current_snapshot (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_in (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_out (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_recv (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_send (PG_FUNCTION_ARGS)
 
Datum pg_visible_in_snapshot (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_xmin (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_xmax (PG_FUNCTION_ARGS)
 
Datum pg_snapshot_xip (PG_FUNCTION_ARGS)
 
Datum pg_xact_status (PG_FUNCTION_ARGS)
 

Macro Definition Documentation

◆ PG_SNAPSHOT_MAX_NXIP

#define PG_SNAPSHOT_MAX_NXIP    ((MaxAllocSize - offsetof(pg_snapshot, xip)) / sizeof(FullTransactionId))

Definition at line 72 of file xid8funcs.c.

◆ PG_SNAPSHOT_SIZE

#define PG_SNAPSHOT_SIZE (   nxip)     (offsetof(pg_snapshot, xip) + sizeof(FullTransactionId) * (nxip))

Definition at line 70 of file xid8funcs.c.

◆ USE_BSEARCH_IF_NXIP_GREATER

#define USE_BSEARCH_IF_NXIP_GREATER   30

Definition at line 48 of file xid8funcs.c.

Function Documentation

◆ buf_add_txid()

static void buf_add_txid ( StringInfo  buf,
FullTransactionId  fxid 
)
static

Definition at line 274 of file xid8funcs.c.

275{
276 pg_snapshot *snap = (pg_snapshot *) buf->data;
277
278 /* do this before possible realloc */
279 snap->nxip++;
280
281 appendBinaryStringInfo(buf, &fxid, sizeof(fxid));
282}
static char * buf
Definition: pg_test_fsync.c:72
void appendBinaryStringInfo(StringInfo str, const void *data, int datalen)
Definition: stringinfo.c:281
uint32 nxip
Definition: xid8funcs.c:63

References appendBinaryStringInfo(), buf, and pg_snapshot::nxip.

Referenced by parse_snapshot().

◆ buf_finalize()

static pg_snapshot * buf_finalize ( StringInfo  buf)
static

Definition at line 285 of file xid8funcs.c.

286{
287 pg_snapshot *snap = (pg_snapshot *) buf->data;
288
289 SET_VARSIZE(snap, buf->len);
290
291 /* buf is not needed anymore */
292 buf->data = NULL;
293 pfree(buf);
294
295 return snap;
296}
void pfree(void *pointer)
Definition: mcxt.c:1521
#define SET_VARSIZE(PTR, len)
Definition: varatt.h:305

References buf, pfree(), and SET_VARSIZE.

Referenced by parse_snapshot().

◆ buf_init()

static StringInfo buf_init ( FullTransactionId  xmin,
FullTransactionId  xmax 
)
static

Definition at line 259 of file xid8funcs.c.

260{
261 pg_snapshot snap;
263
264 snap.xmin = xmin;
265 snap.xmax = xmax;
266 snap.nxip = 0;
267
270 return buf;
271}
StringInfo makeStringInfo(void)
Definition: stringinfo.c:72
FullTransactionId xmax
Definition: xid8funcs.c:65
FullTransactionId xmin
Definition: xid8funcs.c:64
#define PG_SNAPSHOT_SIZE(nxip)
Definition: xid8funcs.c:70

References appendBinaryStringInfo(), buf, makeStringInfo(), pg_snapshot::nxip, PG_SNAPSHOT_SIZE, pg_snapshot::xmax, and pg_snapshot::xmin.

Referenced by parse_snapshot().

◆ cmp_fxid()

static int cmp_fxid ( const void *  aa,
const void *  bb 
)
static

Definition at line 190 of file xid8funcs.c.

191{
192 FullTransactionId a = *(const FullTransactionId *) aa;
193 FullTransactionId b = *(const FullTransactionId *) bb;
194
196 return -1;
198 return 1;
199 return 0;
200}
int b
Definition: isn.c:69
int a
Definition: isn.c:68
#define FullTransactionIdPrecedes(a, b)
Definition: transam.h:51

References a, b, and FullTransactionIdPrecedes.

Referenced by is_visible_fxid(), and sort_snapshot().

◆ is_visible_fxid()

static bool is_visible_fxid ( FullTransactionId  value,
const pg_snapshot snap 
)
static

Definition at line 224 of file xid8funcs.c.

225{
227 return true;
228 else if (!FullTransactionIdPrecedes(value, snap->xmax))
229 return false;
230#ifdef USE_BSEARCH_IF_NXIP_GREATER
231 else if (snap->nxip > USE_BSEARCH_IF_NXIP_GREATER)
232 {
233 void *res;
234
235 res = bsearch(&value, snap->xip, snap->nxip, sizeof(FullTransactionId),
236 cmp_fxid);
237 /* if found, transaction is still in progress */
238 return (res) ? false : true;
239 }
240#endif
241 else
242 {
243 uint32 i;
244
245 for (i = 0; i < snap->nxip; i++)
246 {
247 if (FullTransactionIdEquals(value, snap->xip[i]))
248 return false;
249 }
250 return true;
251 }
252}
uint32_t uint32
Definition: c.h:488
static struct @162 value
return false
Definition: isn.c:130
int i
Definition: isn.c:72
FullTransactionId xip[FLEXIBLE_ARRAY_MEMBER]
Definition: xid8funcs.c:67
#define FullTransactionIdEquals(a, b)
Definition: transam.h:50
static int cmp_fxid(const void *aa, const void *bb)
Definition: xid8funcs.c:190
#define USE_BSEARCH_IF_NXIP_GREATER
Definition: xid8funcs.c:48

References cmp_fxid(), false, FullTransactionIdEquals, FullTransactionIdPrecedes, i, pg_snapshot::nxip, res, USE_BSEARCH_IF_NXIP_GREATER, value, pg_snapshot::xip, pg_snapshot::xmax, and pg_snapshot::xmin.

Referenced by pg_visible_in_snapshot().

◆ parse_snapshot()

static pg_snapshot * parse_snapshot ( const char *  str,
Node escontext 
)
static

Definition at line 302 of file xid8funcs.c.

303{
308 const char *str_start = str;
309 char *endp;
311
312 xmin = FullTransactionIdFromU64(strtou64(str, &endp, 10));
313 if (*endp != ':')
314 goto bad_format;
315 str = endp + 1;
316
317 xmax = FullTransactionIdFromU64(strtou64(str, &endp, 10));
318 if (*endp != ':')
319 goto bad_format;
320 str = endp + 1;
321
322 /* it should look sane */
323 if (!FullTransactionIdIsValid(xmin) ||
325 FullTransactionIdPrecedes(xmax, xmin))
326 goto bad_format;
327
328 /* allocate buffer */
329 buf = buf_init(xmin, xmax);
330
331 /* loop over values */
332 while (*str != '\0')
333 {
334 /* read next value */
335 val = FullTransactionIdFromU64(strtou64(str, &endp, 10));
336 str = endp;
337
338 /* require the input to be in order */
339 if (FullTransactionIdPrecedes(val, xmin) ||
342 goto bad_format;
343
344 /* skip duplicates */
345 if (!FullTransactionIdEquals(val, last_val))
347 last_val = val;
348
349 if (*str == ',')
350 str++;
351 else if (*str != '\0')
352 goto bad_format;
353 }
354
355 return buf_finalize(buf);
356
357bad_format:
358 ereturn(escontext, NULL,
359 (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
360 errmsg("invalid input syntax for type %s: \"%s\"",
361 "pg_snapshot", str_start)));
362}
int errcode(int sqlerrcode)
Definition: elog.c:853
int errmsg(const char *fmt,...)
Definition: elog.c:1070
#define ereturn(context, dummy_value,...)
Definition: elog.h:277
const char * str
long val
Definition: informix.c:689
static FullTransactionId FullTransactionIdFromU64(uint64 value)
Definition: transam.h:81
#define FullTransactionIdFollowsOrEquals(a, b)
Definition: transam.h:54
#define InvalidFullTransactionId
Definition: transam.h:56
#define FullTransactionIdIsValid(x)
Definition: transam.h:55
static pg_snapshot * buf_finalize(StringInfo buf)
Definition: xid8funcs.c:285
static StringInfo buf_init(FullTransactionId xmin, FullTransactionId xmax)
Definition: xid8funcs.c:259
static void buf_add_txid(StringInfo buf, FullTransactionId fxid)
Definition: xid8funcs.c:274

References buf, buf_add_txid(), buf_finalize(), buf_init(), ereturn, errcode(), errmsg(), FullTransactionIdEquals, FullTransactionIdFollowsOrEquals, FullTransactionIdFromU64(), FullTransactionIdIsValid, FullTransactionIdPrecedes, InvalidFullTransactionId, str, and val.

Referenced by pg_snapshot_in().

◆ pg_current_snapshot()

Datum pg_current_snapshot ( PG_FUNCTION_ARGS  )

Definition at line 407 of file xid8funcs.c.

408{
409 pg_snapshot *snap;
410 uint32 nxip,
411 i;
414
416 if (cur == NULL)
417 elog(ERROR, "no active snapshot set");
418
419 /* allocate */
420 nxip = cur->xcnt;
421 snap = palloc(PG_SNAPSHOT_SIZE(nxip));
422
423 /* fill */
424 snap->xmin = widen_snapshot_xid(cur->xmin, next_fxid);
425 snap->xmax = widen_snapshot_xid(cur->xmax, next_fxid);
426 snap->nxip = nxip;
427 for (i = 0; i < nxip; i++)
428 snap->xip[i] = widen_snapshot_xid(cur->xip[i], next_fxid);
429
430 /*
431 * We want them guaranteed to be in ascending order. This also removes
432 * any duplicate xids. Normally, an XID can only be assigned to one
433 * backend, but when preparing a transaction for two-phase commit, there
434 * is a transient state when both the original backend and the dummy
435 * PGPROC entry reserved for the prepared transaction hold the same XID.
436 */
437 sort_snapshot(snap);
438
439 /* set size after sorting, because it may have removed duplicate xips */
440 SET_VARSIZE(snap, PG_SNAPSHOT_SIZE(snap->nxip));
441
442 PG_RETURN_POINTER(snap);
443}
struct cursor * cur
Definition: ecpg.c:29
#define ERROR
Definition: elog.h:39
#define elog(elevel,...)
Definition: elog.h:225
#define PG_RETURN_POINTER(x)
Definition: fmgr.h:361
void * palloc(Size size)
Definition: mcxt.c:1317
Snapshot GetActiveSnapshot(void)
Definition: snapmgr.c:728
FullTransactionId ReadNextFullTransactionId(void)
Definition: varsup.c:288
static void sort_snapshot(pg_snapshot *snap)
Definition: xid8funcs.c:210
static FullTransactionId widen_snapshot_xid(TransactionId xid, FullTransactionId next_fxid)
Definition: xid8funcs.c:164

References cur, elog, ERROR, GetActiveSnapshot(), i, pg_snapshot::nxip, palloc(), PG_RETURN_POINTER, PG_SNAPSHOT_SIZE, ReadNextFullTransactionId(), SET_VARSIZE, sort_snapshot(), widen_snapshot_xid(), pg_snapshot::xip, pg_snapshot::xmax, and pg_snapshot::xmin.

◆ pg_current_xact_id()

Datum pg_current_xact_id ( PG_FUNCTION_ARGS  )

Definition at line 371 of file xid8funcs.c.

372{
373 /*
374 * Must prevent during recovery because if an xid is not assigned we try
375 * to assign one, which would fail. Programs already rely on this function
376 * to always return a valid current xid, so we should not change this to
377 * return NULL or similar invalid xid.
378 */
379 PreventCommandDuringRecovery("pg_current_xact_id()");
380
382}
void PreventCommandDuringRecovery(const char *cmdname)
Definition: utility.c:441
FullTransactionId GetTopFullTransactionId(void)
Definition: xact.c:482
#define PG_RETURN_FULLTRANSACTIONID(X)
Definition: xid8.h:30

References GetTopFullTransactionId(), PG_RETURN_FULLTRANSACTIONID, and PreventCommandDuringRecovery().

◆ pg_current_xact_id_if_assigned()

Datum pg_current_xact_id_if_assigned ( PG_FUNCTION_ARGS  )

Definition at line 389 of file xid8funcs.c.

390{
392
393 if (!FullTransactionIdIsValid(topfxid))
395
397}
#define PG_RETURN_NULL()
Definition: fmgr.h:345
FullTransactionId GetTopFullTransactionIdIfAny(void)
Definition: xact.c:498

References FullTransactionIdIsValid, GetTopFullTransactionIdIfAny(), PG_RETURN_FULLTRANSACTIONID, and PG_RETURN_NULL.

◆ pg_snapshot_in()

Datum pg_snapshot_in ( PG_FUNCTION_ARGS  )

Definition at line 451 of file xid8funcs.c.

452{
453 char *str = PG_GETARG_CSTRING(0);
454 pg_snapshot *snap;
455
456 snap = parse_snapshot(str, fcinfo->context);
457
458 PG_RETURN_POINTER(snap);
459}
#define PG_GETARG_CSTRING(n)
Definition: fmgr.h:277
static pg_snapshot * parse_snapshot(const char *str, Node *escontext)
Definition: xid8funcs.c:302

References parse_snapshot(), PG_GETARG_CSTRING, PG_RETURN_POINTER, and str.

◆ pg_snapshot_out()

Datum pg_snapshot_out ( PG_FUNCTION_ARGS  )

Definition at line 467 of file xid8funcs.c.

468{
471 uint32 i;
472
474
479
480 for (i = 0; i < snap->nxip; i++)
481 {
482 if (i > 0)
486 }
487
489}
#define UINT64_FORMAT
Definition: c.h:507
#define PG_GETARG_VARLENA_P(n)
Definition: fmgr.h:287
#define PG_RETURN_CSTRING(x)
Definition: fmgr.h:362
void appendStringInfo(StringInfo str, const char *fmt,...)
Definition: stringinfo.c:145
void appendStringInfoChar(StringInfo str, char ch)
Definition: stringinfo.c:242
void initStringInfo(StringInfo str)
Definition: stringinfo.c:97
#define U64FromFullTransactionId(x)
Definition: transam.h:49

References appendStringInfo(), appendStringInfoChar(), i, initStringInfo(), pg_snapshot::nxip, PG_GETARG_VARLENA_P, PG_RETURN_CSTRING, str, U64FromFullTransactionId, UINT64_FORMAT, pg_snapshot::xip, pg_snapshot::xmax, and pg_snapshot::xmin.

◆ pg_snapshot_recv()

Datum pg_snapshot_recv ( PG_FUNCTION_ARGS  )

Definition at line 499 of file xid8funcs.c.

500{
502 pg_snapshot *snap;
504 int nxip;
505 int i;
508
509 /* load and validate nxip */
510 nxip = pq_getmsgint(buf, 4);
511 if (nxip < 0 || nxip > PG_SNAPSHOT_MAX_NXIP)
512 goto bad_format;
513
516 if (!FullTransactionIdIsValid(xmin) ||
518 FullTransactionIdPrecedes(xmax, xmin))
519 goto bad_format;
520
521 snap = palloc(PG_SNAPSHOT_SIZE(nxip));
522 snap->xmin = xmin;
523 snap->xmax = xmax;
524
525 for (i = 0; i < nxip; i++)
526 {
529
530 if (FullTransactionIdPrecedes(cur, last) ||
533 goto bad_format;
534
535 /* skip duplicate xips */
536 if (FullTransactionIdEquals(cur, last))
537 {
538 i--;
539 nxip--;
540 continue;
541 }
542
543 snap->xip[i] = cur;
544 last = cur;
545 }
546 snap->nxip = nxip;
547 SET_VARSIZE(snap, PG_SNAPSHOT_SIZE(nxip));
548 PG_RETURN_POINTER(snap);
549
550bad_format:
552 (errcode(ERRCODE_INVALID_BINARY_REPRESENTATION),
553 errmsg("invalid external pg_snapshot data")));
554 PG_RETURN_POINTER(NULL); /* keep compiler quiet */
555}
uint64_t uint64
Definition: c.h:489
#define ereport(elevel,...)
Definition: elog.h:149
#define PG_GETARG_POINTER(n)
Definition: fmgr.h:276
unsigned int pq_getmsgint(StringInfo msg, int b)
Definition: pqformat.c:415
int64 pq_getmsgint64(StringInfo msg)
Definition: pqformat.c:453
StringInfoData * StringInfo
Definition: stringinfo.h:54
#define PG_SNAPSHOT_MAX_NXIP
Definition: xid8funcs.c:72

References buf, cur, ereport, errcode(), errmsg(), ERROR, FullTransactionIdEquals, FullTransactionIdFromU64(), FullTransactionIdIsValid, FullTransactionIdPrecedes, i, InvalidFullTransactionId, pg_snapshot::nxip, palloc(), PG_GETARG_POINTER, PG_RETURN_POINTER, PG_SNAPSHOT_MAX_NXIP, PG_SNAPSHOT_SIZE, pq_getmsgint(), pq_getmsgint64(), SET_VARSIZE, pg_snapshot::xip, pg_snapshot::xmax, and pg_snapshot::xmin.

◆ pg_snapshot_send()

Datum pg_snapshot_send ( PG_FUNCTION_ARGS  )

Definition at line 565 of file xid8funcs.c.

566{
569 uint32 i;
570
572 pq_sendint32(&buf, snap->nxip);
575 for (i = 0; i < snap->nxip; i++)
578}
int64_t int64
Definition: c.h:485
#define PG_RETURN_BYTEA_P(x)
Definition: fmgr.h:371
void pq_begintypsend(StringInfo buf)
Definition: pqformat.c:326
bytea * pq_endtypsend(StringInfo buf)
Definition: pqformat.c:346
static void pq_sendint32(StringInfo buf, uint32 i)
Definition: pqformat.h:144
static void pq_sendint64(StringInfo buf, uint64 i)
Definition: pqformat.h:152

References buf, i, pg_snapshot::nxip, PG_GETARG_VARLENA_P, PG_RETURN_BYTEA_P, pq_begintypsend(), pq_endtypsend(), pq_sendint32(), pq_sendint64(), U64FromFullTransactionId, pg_snapshot::xip, pg_snapshot::xmax, and pg_snapshot::xmin.

◆ pg_snapshot_xip()

Datum pg_snapshot_xip ( PG_FUNCTION_ARGS  )

Definition at line 626 of file xid8funcs.c.

627{
628 FuncCallContext *fctx;
629 pg_snapshot *snap;
631
632 /* on first call initialize fctx and get copy of snapshot */
633 if (SRF_IS_FIRSTCALL())
634 {
636
637 fctx = SRF_FIRSTCALL_INIT();
638
639 /* make a copy of user snapshot */
641 memcpy(snap, arg, VARSIZE(arg));
642
643 fctx->user_fctx = snap;
644 }
645
646 /* return values one-by-one */
647 fctx = SRF_PERCALL_SETUP();
648 snap = fctx->user_fctx;
649 if (fctx->call_cntr < snap->nxip)
650 {
651 value = snap->xip[fctx->call_cntr];
653 }
654 else
655 {
656 SRF_RETURN_DONE(fctx);
657 }
658}
#define SRF_IS_FIRSTCALL()
Definition: funcapi.h:304
#define SRF_PERCALL_SETUP()
Definition: funcapi.h:308
#define SRF_RETURN_NEXT(_funcctx, _result)
Definition: funcapi.h:310
#define SRF_FIRSTCALL_INIT()
Definition: funcapi.h:306
#define SRF_RETURN_DONE(_funcctx)
Definition: funcapi.h:328
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:1181
void * arg
void * user_fctx
Definition: funcapi.h:82
uint64 call_cntr
Definition: funcapi.h:65
MemoryContext multi_call_memory_ctx
Definition: funcapi.h:101
#define VARSIZE(PTR)
Definition: varatt.h:279
static Datum FullTransactionIdGetDatum(FullTransactionId X)
Definition: xid8.h:24

References arg, FuncCallContext::call_cntr, FullTransactionIdGetDatum(), MemoryContextAlloc(), FuncCallContext::multi_call_memory_ctx, pg_snapshot::nxip, PG_GETARG_VARLENA_P, SRF_FIRSTCALL_INIT, SRF_IS_FIRSTCALL, SRF_PERCALL_SETUP, SRF_RETURN_DONE, SRF_RETURN_NEXT, FuncCallContext::user_fctx, value, VARSIZE, and pg_snapshot::xip.

◆ pg_snapshot_xmax()

Datum pg_snapshot_xmax ( PG_FUNCTION_ARGS  )

Definition at line 613 of file xid8funcs.c.

614{
616
618}

References PG_GETARG_VARLENA_P, PG_RETURN_FULLTRANSACTIONID, and pg_snapshot::xmax.

◆ pg_snapshot_xmin()

Datum pg_snapshot_xmin ( PG_FUNCTION_ARGS  )

Definition at line 600 of file xid8funcs.c.

601{
603
605}

References PG_GETARG_VARLENA_P, PG_RETURN_FULLTRANSACTIONID, and pg_snapshot::xmin.

◆ pg_visible_in_snapshot()

Datum pg_visible_in_snapshot ( PG_FUNCTION_ARGS  )

Definition at line 586 of file xid8funcs.c.

587{
590
592}
#define PG_RETURN_BOOL(x)
Definition: fmgr.h:359
#define PG_GETARG_FULLTRANSACTIONID(X)
Definition: xid8.h:29
static bool is_visible_fxid(FullTransactionId value, const pg_snapshot *snap)
Definition: xid8funcs.c:224

References is_visible_fxid(), PG_GETARG_FULLTRANSACTIONID, PG_GETARG_VARLENA_P, PG_RETURN_BOOL, and value.

◆ pg_xact_status()

Datum pg_xact_status ( PG_FUNCTION_ARGS  )

Definition at line 671 of file xid8funcs.c.

672{
673 const char *status;
675 TransactionId xid;
676
677 /*
678 * We must protect against concurrent truncation of clog entries to avoid
679 * an I/O error on SLRU lookup.
680 */
681 LWLockAcquire(XactTruncationLock, LW_SHARED);
682 if (TransactionIdInRecentPast(fxid, &xid))
683 {
685
686 /*
687 * Like when doing visibility checks on a row, check whether the
688 * transaction is still in progress before looking into the CLOG.
689 * Otherwise we would incorrectly return "committed" for a transaction
690 * that is committing and has already updated the CLOG, but hasn't
691 * removed its XID from the proc array yet. (See comment on that race
692 * condition at the top of heapam_visibility.c)
693 */
695 status = "in progress";
696 else if (TransactionIdDidCommit(xid))
697 status = "committed";
698 else
699 {
700 /* it must have aborted or crashed */
701 status = "aborted";
702 }
703 }
704 else
705 {
706 status = NULL;
707 }
708 LWLockRelease(XactTruncationLock);
709
710 if (status == NULL)
712 else
714}
#define Assert(condition)
Definition: c.h:815
uint32 TransactionId
Definition: c.h:609
#define PG_RETURN_TEXT_P(x)
Definition: fmgr.h:372
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1168
void LWLockRelease(LWLock *lock)
Definition: lwlock.c:1781
@ LW_SHARED
Definition: lwlock.h:115
bool TransactionIdIsInProgress(TransactionId xid)
Definition: procarray.c:1402
bool TransactionIdDidCommit(TransactionId transactionId)
Definition: transam.c:126
#define TransactionIdIsValid(xid)
Definition: transam.h:41
text * cstring_to_text(const char *s)
Definition: varlena.c:184
static bool TransactionIdInRecentPast(FullTransactionId fxid, TransactionId *extracted_xid)
Definition: xid8funcs.c:97

References Assert, cstring_to_text(), LW_SHARED, LWLockAcquire(), LWLockRelease(), PG_GETARG_FULLTRANSACTIONID, PG_RETURN_NULL, PG_RETURN_TEXT_P, TransactionIdDidCommit(), TransactionIdInRecentPast(), TransactionIdIsInProgress(), and TransactionIdIsValid.

◆ sort_snapshot()

static void sort_snapshot ( pg_snapshot snap)
static

Definition at line 210 of file xid8funcs.c.

211{
212 if (snap->nxip > 1)
213 {
214 qsort(snap->xip, snap->nxip, sizeof(FullTransactionId), cmp_fxid);
215 snap->nxip = qunique(snap->xip, snap->nxip, sizeof(FullTransactionId),
216 cmp_fxid);
217 }
218}
#define qsort(a, b, c, d)
Definition: port.h:474
static size_t qunique(void *array, size_t elements, size_t width, int(*compare)(const void *, const void *))
Definition: qunique.h:21

References cmp_fxid(), pg_snapshot::nxip, qsort, qunique(), and pg_snapshot::xip.

Referenced by pg_current_snapshot().

◆ StaticAssertDecl()

StaticAssertDecl ( MAX_BACKENDS *2<=  PG_SNAPSHOT_MAX_NXIP,
"possible overflow in pg_current_snapshot()"   
)

◆ TransactionIdInRecentPast()

static bool TransactionIdInRecentPast ( FullTransactionId  fxid,
TransactionId extracted_xid 
)
static

Definition at line 97 of file xid8funcs.c.

98{
100 uint32 now_epoch;
101 TransactionId now_epoch_next_xid;
102 FullTransactionId now_fullxid;
103 TransactionId oldest_xid;
104 FullTransactionId oldest_fxid;
105
106 now_fullxid = ReadNextFullTransactionId();
107 now_epoch_next_xid = XidFromFullTransactionId(now_fullxid);
108 now_epoch = EpochFromFullTransactionId(now_fullxid);
109
110 if (extracted_xid != NULL)
111 *extracted_xid = xid;
112
113 if (!TransactionIdIsValid(xid))
114 return false;
115
116 /* For non-normal transaction IDs, we can ignore the epoch. */
117 if (!TransactionIdIsNormal(xid))
118 return true;
119
120 /* If the transaction ID is in the future, throw an error. */
121 if (!FullTransactionIdPrecedes(fxid, now_fullxid))
123 (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
124 errmsg("transaction ID %llu is in the future",
125 (unsigned long long) U64FromFullTransactionId(fxid))));
126
127 /*
128 * TransamVariables->oldestClogXid is protected by XactTruncationLock, but
129 * we don't acquire that lock here. Instead, we require the caller to
130 * acquire it, because the caller is presumably going to look up the
131 * returned XID. If we took and released the lock within this function, a
132 * CLOG truncation could occur before the caller finished with the XID.
133 */
134 Assert(LWLockHeldByMe(XactTruncationLock));
135
136 /*
137 * If fxid is not older than TransamVariables->oldestClogXid, the relevant
138 * CLOG entry is guaranteed to still exist. Convert
139 * TransamVariables->oldestClogXid into a FullTransactionId to compare it
140 * with fxid. Determine the right epoch knowing that oldest_fxid
141 * shouldn't be more than 2^31 older than now_fullxid.
142 */
143 oldest_xid = TransamVariables->oldestClogXid;
144 Assert(TransactionIdPrecedesOrEquals(oldest_xid, now_epoch_next_xid));
145 if (oldest_xid <= now_epoch_next_xid)
146 {
147 oldest_fxid = FullTransactionIdFromEpochAndXid(now_epoch, oldest_xid);
148 }
149 else
150 {
151 Assert(now_epoch > 0);
152 oldest_fxid = FullTransactionIdFromEpochAndXid(now_epoch - 1, oldest_xid);
153 }
154 return !FullTransactionIdPrecedes(fxid, oldest_fxid);
155}
bool LWLockHeldByMe(LWLock *lock)
Definition: lwlock.c:1893
TransactionId oldestClogXid
Definition: transam.h:253
bool TransactionIdPrecedesOrEquals(TransactionId id1, TransactionId id2)
Definition: transam.c:299
#define EpochFromFullTransactionId(x)
Definition: transam.h:47
#define XidFromFullTransactionId(x)
Definition: transam.h:48
static FullTransactionId FullTransactionIdFromEpochAndXid(uint32 epoch, TransactionId xid)
Definition: transam.h:71
#define TransactionIdIsNormal(xid)
Definition: transam.h:42
TransamVariablesData * TransamVariables
Definition: varsup.c:34

References Assert, EpochFromFullTransactionId, ereport, errcode(), errmsg(), ERROR, FullTransactionIdFromEpochAndXid(), FullTransactionIdPrecedes, LWLockHeldByMe(), TransamVariablesData::oldestClogXid, ReadNextFullTransactionId(), TransactionIdIsNormal, TransactionIdIsValid, TransactionIdPrecedesOrEquals(), TransamVariables, U64FromFullTransactionId, and XidFromFullTransactionId.

Referenced by pg_xact_status().

◆ widen_snapshot_xid()

static FullTransactionId widen_snapshot_xid ( TransactionId  xid,
FullTransactionId  next_fxid 
)
static

Definition at line 164 of file xid8funcs.c.

165{
166 TransactionId next_xid = XidFromFullTransactionId(next_fxid);
168
169 /* Special transaction ID. */
170 if (!TransactionIdIsNormal(xid))
172
173 /*
174 * The 64 bit result must be <= next_fxid, since next_fxid hadn't been
175 * issued yet when the snapshot was created. Every TransactionId in the
176 * snapshot must therefore be from the same epoch as next_fxid, or the
177 * epoch before. We know this because next_fxid is never allow to get
178 * more than one epoch ahead of the TransactionIds in any snapshot.
179 */
180 if (xid > next_xid)
181 epoch--;
182
184}
static const unsigned __int64 epoch

References epoch, EpochFromFullTransactionId, FullTransactionIdFromEpochAndXid(), TransactionIdIsNormal, and XidFromFullTransactionId.

Referenced by pg_current_snapshot().