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freelist.c File Reference
#include "postgres.h"
#include "pgstat.h"
#include "port/atomics.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
#include "storage/proc.h"
Include dependency graph for freelist.c:

Go to the source code of this file.

Data Structures

struct  BufferStrategyControl
 
struct  BufferAccessStrategyData
 

Macros

#define INT_ACCESS_ONCE(var)   ((int)(*((volatile int *)&(var))))
 

Typedefs

typedef struct BufferAccessStrategyData BufferAccessStrategyData
 

Functions

static BufferDescGetBufferFromRing (BufferAccessStrategy strategy, uint32 *buf_state)
 
static void AddBufferToRing (BufferAccessStrategy strategy, BufferDesc *buf)
 
static uint32 ClockSweepTick (void)
 
bool have_free_buffer (void)
 
BufferDescStrategyGetBuffer (BufferAccessStrategy strategy, uint32 *buf_state, bool *from_ring)
 
void StrategyFreeBuffer (BufferDesc *buf)
 
int StrategySyncStart (uint32 *complete_passes, uint32 *num_buf_alloc)
 
void StrategyNotifyBgWriter (int bgwprocno)
 
Size StrategyShmemSize (void)
 
void StrategyInitialize (bool init)
 
BufferAccessStrategy GetAccessStrategy (BufferAccessStrategyType btype)
 
BufferAccessStrategy GetAccessStrategyWithSize (BufferAccessStrategyType btype, int ring_size_kb)
 
int GetAccessStrategyBufferCount (BufferAccessStrategy strategy)
 
int GetAccessStrategyPinLimit (BufferAccessStrategy strategy)
 
void FreeAccessStrategy (BufferAccessStrategy strategy)
 
IOContext IOContextForStrategy (BufferAccessStrategy strategy)
 
bool StrategyRejectBuffer (BufferAccessStrategy strategy, BufferDesc *buf, bool from_ring)
 

Variables

static BufferStrategyControlStrategyControl = NULL
 

Macro Definition Documentation

◆ INT_ACCESS_ONCE

#define INT_ACCESS_ONCE (   var)    ((int)(*((volatile int *)&(var))))

Definition at line 24 of file freelist.c.

Typedef Documentation

◆ BufferAccessStrategyData

Function Documentation

◆ AddBufferToRing()

static void AddBufferToRing ( BufferAccessStrategy  strategy,
BufferDesc buf 
)
static

Definition at line 748 of file freelist.c.

749 {
750  strategy->buffers[strategy->current] = BufferDescriptorGetBuffer(buf);
751 }
static Buffer BufferDescriptorGetBuffer(const BufferDesc *bdesc)
static char * buf
Definition: pg_test_fsync.c:72
Buffer buffers[FLEXIBLE_ARRAY_MEMBER]
Definition: freelist.c:91

References buf, BufferDescriptorGetBuffer(), BufferAccessStrategyData::buffers, and BufferAccessStrategyData::current.

Referenced by StrategyGetBuffer().

◆ ClockSweepTick()

static uint32 ClockSweepTick ( void  )
inlinestatic

Definition at line 108 of file freelist.c.

109 {
110  uint32 victim;
111 
112  /*
113  * Atomically move hand ahead one buffer - if there's several processes
114  * doing this, this can lead to buffers being returned slightly out of
115  * apparent order.
116  */
117  victim =
119 
120  if (victim >= NBuffers)
121  {
122  uint32 originalVictim = victim;
123 
124  /* always wrap what we look up in BufferDescriptors */
125  victim = victim % NBuffers;
126 
127  /*
128  * If we're the one that just caused a wraparound, force
129  * completePasses to be incremented while holding the spinlock. We
130  * need the spinlock so StrategySyncStart() can return a consistent
131  * value consisting of nextVictimBuffer and completePasses.
132  */
133  if (victim == 0)
134  {
135  uint32 expected;
136  uint32 wrapped;
137  bool success = false;
138 
139  expected = originalVictim + 1;
140 
141  while (!success)
142  {
143  /*
144  * Acquire the spinlock while increasing completePasses. That
145  * allows other readers to read nextVictimBuffer and
146  * completePasses in a consistent manner which is required for
147  * StrategySyncStart(). In theory delaying the increment
148  * could lead to an overflow of nextVictimBuffers, but that's
149  * highly unlikely and wouldn't be particularly harmful.
150  */
152 
153  wrapped = expected % NBuffers;
154 
156  &expected, wrapped);
157  if (success)
160  }
161  }
162  }
163  return victim;
164 }
static bool pg_atomic_compare_exchange_u32(volatile pg_atomic_uint32 *ptr, uint32 *expected, uint32 newval)
Definition: atomics.h:349
static uint32 pg_atomic_fetch_add_u32(volatile pg_atomic_uint32 *ptr, int32 add_)
Definition: atomics.h:366
unsigned int uint32
Definition: c.h:518
static BufferStrategyControl * StrategyControl
Definition: freelist.c:65
int NBuffers
Definition: globals.c:141
static bool success
Definition: initdb.c:186
#define SpinLockRelease(lock)
Definition: spin.h:61
#define SpinLockAcquire(lock)
Definition: spin.h:59
pg_atomic_uint32 nextVictimBuffer
Definition: freelist.c:40
slock_t buffer_strategy_lock
Definition: freelist.c:33

References BufferStrategyControl::buffer_strategy_lock, BufferStrategyControl::completePasses, NBuffers, BufferStrategyControl::nextVictimBuffer, pg_atomic_compare_exchange_u32(), pg_atomic_fetch_add_u32(), SpinLockAcquire, SpinLockRelease, StrategyControl, and success.

Referenced by StrategyGetBuffer().

◆ FreeAccessStrategy()

void FreeAccessStrategy ( BufferAccessStrategy  strategy)

Definition at line 681 of file freelist.c.

682 {
683  /* don't crash if called on a "default" strategy */
684  if (strategy != NULL)
685  pfree(strategy);
686 }
void pfree(void *pointer)
Definition: mcxt.c:1521

References pfree().

Referenced by blgetbitmap(), FreeBulkInsertState(), heap_endscan(), initscan(), parallel_vacuum_main(), and RelationCopyStorageUsingBuffer().

◆ GetAccessStrategy()

BufferAccessStrategy GetAccessStrategy ( BufferAccessStrategyType  btype)

Definition at line 541 of file freelist.c.

542 {
543  int ring_size_kb;
544 
545  /*
546  * Select ring size to use. See buffer/README for rationales.
547  *
548  * Note: if you change the ring size for BAS_BULKREAD, see also
549  * SYNC_SCAN_REPORT_INTERVAL in access/heap/syncscan.c.
550  */
551  switch (btype)
552  {
553  case BAS_NORMAL:
554  /* if someone asks for NORMAL, just give 'em a "default" object */
555  return NULL;
556 
557  case BAS_BULKREAD:
558  ring_size_kb = 256;
559  break;
560  case BAS_BULKWRITE:
561  ring_size_kb = 16 * 1024;
562  break;
563  case BAS_VACUUM:
564  ring_size_kb = 2048;
565  break;
566 
567  default:
568  elog(ERROR, "unrecognized buffer access strategy: %d",
569  (int) btype);
570  return NULL; /* keep compiler quiet */
571  }
572 
573  return GetAccessStrategyWithSize(btype, ring_size_kb);
574 }
@ BAS_BULKREAD
Definition: bufmgr.h:36
@ BAS_NORMAL
Definition: bufmgr.h:35
@ BAS_VACUUM
Definition: bufmgr.h:39
@ BAS_BULKWRITE
Definition: bufmgr.h:38
#define ERROR
Definition: elog.h:39
#define elog(elevel,...)
Definition: elog.h:225
BufferAccessStrategy GetAccessStrategyWithSize(BufferAccessStrategyType btype, int ring_size_kb)
Definition: freelist.c:584

References BAS_BULKREAD, BAS_BULKWRITE, BAS_NORMAL, BAS_VACUUM, elog, ERROR, and GetAccessStrategyWithSize().

Referenced by blgetbitmap(), bt_check_every_level(), collect_corrupt_items(), collect_visibility_data(), GetBulkInsertState(), initscan(), pgstat_index(), pgstathashindex(), pgstatindex_impl(), RelationCopyStorageUsingBuffer(), ScanSourceDatabasePgClass(), statapprox_heap(), and verify_heapam().

◆ GetAccessStrategyBufferCount()

int GetAccessStrategyBufferCount ( BufferAccessStrategy  strategy)

Definition at line 624 of file freelist.c.

625 {
626  if (strategy == NULL)
627  return 0;
628 
629  return strategy->nbuffers;
630 }

References BufferAccessStrategyData::nbuffers.

Referenced by parallel_vacuum_init().

◆ GetAccessStrategyPinLimit()

int GetAccessStrategyPinLimit ( BufferAccessStrategy  strategy)

Definition at line 647 of file freelist.c.

648 {
649  if (strategy == NULL)
650  return NBuffers;
651 
652  switch (strategy->btype)
653  {
654  case BAS_BULKREAD:
655 
656  /*
657  * Since BAS_BULKREAD uses StrategyRejectBuffer(), dirty buffers
658  * shouldn't be a problem and the caller is free to pin up to the
659  * entire ring at once.
660  */
661  return strategy->nbuffers;
662 
663  default:
664 
665  /*
666  * Tell caller not to pin more than half the buffers in the ring.
667  * This is a trade-off between look ahead distance and deferring
668  * writeback and associated WAL traffic.
669  */
670  return strategy->nbuffers / 2;
671  }
672 }
BufferAccessStrategyType btype
Definition: freelist.c:75

References BAS_BULKREAD, BufferAccessStrategyData::btype, BufferAccessStrategyData::nbuffers, and NBuffers.

Referenced by read_stream_begin_impl().

◆ GetAccessStrategyWithSize()

BufferAccessStrategy GetAccessStrategyWithSize ( BufferAccessStrategyType  btype,
int  ring_size_kb 
)

Definition at line 584 of file freelist.c.

585 {
586  int ring_buffers;
587  BufferAccessStrategy strategy;
588 
589  Assert(ring_size_kb >= 0);
590 
591  /* Figure out how many buffers ring_size_kb is */
592  ring_buffers = ring_size_kb / (BLCKSZ / 1024);
593 
594  /* 0 means unlimited, so no BufferAccessStrategy required */
595  if (ring_buffers == 0)
596  return NULL;
597 
598  /* Cap to 1/8th of shared_buffers */
599  ring_buffers = Min(NBuffers / 8, ring_buffers);
600 
601  /* NBuffers should never be less than 16, so this shouldn't happen */
602  Assert(ring_buffers > 0);
603 
604  /* Allocate the object and initialize all elements to zeroes */
605  strategy = (BufferAccessStrategy)
606  palloc0(offsetof(BufferAccessStrategyData, buffers) +
607  ring_buffers * sizeof(Buffer));
608 
609  /* Set fields that don't start out zero */
610  strategy->btype = btype;
611  strategy->nbuffers = ring_buffers;
612 
613  return strategy;
614 }
int Buffer
Definition: buf.h:23
struct BufferAccessStrategyData * BufferAccessStrategy
Definition: buf.h:44
#define Min(x, y)
Definition: c.h:1009
#define Assert(condition)
Definition: c.h:863
void * palloc0(Size size)
Definition: mcxt.c:1347

References Assert, BufferAccessStrategyData::btype, Min, BufferAccessStrategyData::nbuffers, NBuffers, and palloc0().

Referenced by do_autovacuum(), ExecVacuum(), GetAccessStrategy(), and parallel_vacuum_main().

◆ GetBufferFromRing()

static BufferDesc * GetBufferFromRing ( BufferAccessStrategy  strategy,
uint32 buf_state 
)
static

Definition at line 695 of file freelist.c.

696 {
697  BufferDesc *buf;
698  Buffer bufnum;
699  uint32 local_buf_state; /* to avoid repeated (de-)referencing */
700 
701 
702  /* Advance to next ring slot */
703  if (++strategy->current >= strategy->nbuffers)
704  strategy->current = 0;
705 
706  /*
707  * If the slot hasn't been filled yet, tell the caller to allocate a new
708  * buffer with the normal allocation strategy. He will then fill this
709  * slot by calling AddBufferToRing with the new buffer.
710  */
711  bufnum = strategy->buffers[strategy->current];
712  if (bufnum == InvalidBuffer)
713  return NULL;
714 
715  /*
716  * If the buffer is pinned we cannot use it under any circumstances.
717  *
718  * If usage_count is 0 or 1 then the buffer is fair game (we expect 1,
719  * since our own previous usage of the ring element would have left it
720  * there, but it might've been decremented by clock sweep since then). A
721  * higher usage_count indicates someone else has touched the buffer, so we
722  * shouldn't re-use it.
723  */
724  buf = GetBufferDescriptor(bufnum - 1);
725  local_buf_state = LockBufHdr(buf);
726  if (BUF_STATE_GET_REFCOUNT(local_buf_state) == 0
727  && BUF_STATE_GET_USAGECOUNT(local_buf_state) <= 1)
728  {
729  *buf_state = local_buf_state;
730  return buf;
731  }
732  UnlockBufHdr(buf, local_buf_state);
733 
734  /*
735  * Tell caller to allocate a new buffer with the normal allocation
736  * strategy. He'll then replace this ring element via AddBufferToRing.
737  */
738  return NULL;
739 }
#define InvalidBuffer
Definition: buf.h:25
static BufferDesc * GetBufferDescriptor(uint32 id)
static void UnlockBufHdr(BufferDesc *desc, uint32 buf_state)
#define BUF_STATE_GET_USAGECOUNT(state)
Definition: buf_internals.h:51
#define BUF_STATE_GET_REFCOUNT(state)
Definition: buf_internals.h:50
uint32 LockBufHdr(BufferDesc *desc)
Definition: bufmgr.c:5761

References buf, BUF_STATE_GET_REFCOUNT, BUF_STATE_GET_USAGECOUNT, BufferAccessStrategyData::buffers, BufferAccessStrategyData::current, GetBufferDescriptor(), InvalidBuffer, LockBufHdr(), BufferAccessStrategyData::nbuffers, and UnlockBufHdr().

Referenced by StrategyGetBuffer().

◆ have_free_buffer()

bool have_free_buffer ( void  )

Definition at line 175 of file freelist.c.

176 {
178  return true;
179  else
180  return false;
181 }

References BufferStrategyControl::firstFreeBuffer, and StrategyControl.

Referenced by apw_load_buffers(), and autoprewarm_database_main().

◆ IOContextForStrategy()

IOContext IOContextForStrategy ( BufferAccessStrategy  strategy)

Definition at line 758 of file freelist.c.

759 {
760  if (!strategy)
761  return IOCONTEXT_NORMAL;
762 
763  switch (strategy->btype)
764  {
765  case BAS_NORMAL:
766 
767  /*
768  * Currently, GetAccessStrategy() returns NULL for
769  * BufferAccessStrategyType BAS_NORMAL, so this case is
770  * unreachable.
771  */
772  pg_unreachable();
773  return IOCONTEXT_NORMAL;
774  case BAS_BULKREAD:
775  return IOCONTEXT_BULKREAD;
776  case BAS_BULKWRITE:
777  return IOCONTEXT_BULKWRITE;
778  case BAS_VACUUM:
779  return IOCONTEXT_VACUUM;
780  }
781 
782  elog(ERROR, "unrecognized BufferAccessStrategyType: %d", strategy->btype);
783  pg_unreachable();
784 }
#define pg_unreachable()
Definition: c.h:311
@ IOCONTEXT_NORMAL
Definition: pgstat.h:324
@ IOCONTEXT_VACUUM
Definition: pgstat.h:325
@ IOCONTEXT_BULKREAD
Definition: pgstat.h:322
@ IOCONTEXT_BULKWRITE
Definition: pgstat.h:323

References BAS_BULKREAD, BAS_BULKWRITE, BAS_NORMAL, BAS_VACUUM, BufferAccessStrategyData::btype, elog, ERROR, IOCONTEXT_BULKREAD, IOCONTEXT_BULKWRITE, IOCONTEXT_NORMAL, IOCONTEXT_VACUUM, and pg_unreachable.

Referenced by ExtendBufferedRelShared(), PinBufferForBlock(), and WaitReadBuffers().

◆ StrategyFreeBuffer()

void StrategyFreeBuffer ( BufferDesc buf)

Definition at line 363 of file freelist.c.

364 {
366 
367  /*
368  * It is possible that we are told to put something in the freelist that
369  * is already in it; don't screw up the list if so.
370  */
371  if (buf->freeNext == FREENEXT_NOT_IN_LIST)
372  {
373  buf->freeNext = StrategyControl->firstFreeBuffer;
374  if (buf->freeNext < 0)
377  }
378 
380 }
#define FREENEXT_NOT_IN_LIST

References buf, BufferStrategyControl::buffer_strategy_lock, BufferStrategyControl::firstFreeBuffer, FREENEXT_NOT_IN_LIST, BufferStrategyControl::lastFreeBuffer, SpinLockAcquire, SpinLockRelease, and StrategyControl.

Referenced by BufferAlloc(), ExtendBufferedRelShared(), and InvalidateBuffer().

◆ StrategyGetBuffer()

BufferDesc* StrategyGetBuffer ( BufferAccessStrategy  strategy,
uint32 buf_state,
bool from_ring 
)

Definition at line 196 of file freelist.c.

197 {
198  BufferDesc *buf;
199  int bgwprocno;
200  int trycounter;
201  uint32 local_buf_state; /* to avoid repeated (de-)referencing */
202 
203  *from_ring = false;
204 
205  /*
206  * If given a strategy object, see whether it can select a buffer. We
207  * assume strategy objects don't need buffer_strategy_lock.
208  */
209  if (strategy != NULL)
210  {
211  buf = GetBufferFromRing(strategy, buf_state);
212  if (buf != NULL)
213  {
214  *from_ring = true;
215  return buf;
216  }
217  }
218 
219  /*
220  * If asked, we need to waken the bgwriter. Since we don't want to rely on
221  * a spinlock for this we force a read from shared memory once, and then
222  * set the latch based on that value. We need to go through that length
223  * because otherwise bgwprocno might be reset while/after we check because
224  * the compiler might just reread from memory.
225  *
226  * This can possibly set the latch of the wrong process if the bgwriter
227  * dies in the wrong moment. But since PGPROC->procLatch is never
228  * deallocated the worst consequence of that is that we set the latch of
229  * some arbitrary process.
230  */
232  if (bgwprocno != -1)
233  {
234  /* reset bgwprocno first, before setting the latch */
236 
237  /*
238  * Not acquiring ProcArrayLock here which is slightly icky. It's
239  * actually fine because procLatch isn't ever freed, so we just can
240  * potentially set the wrong process' (or no process') latch.
241  */
242  SetLatch(&ProcGlobal->allProcs[bgwprocno].procLatch);
243  }
244 
245  /*
246  * We count buffer allocation requests so that the bgwriter can estimate
247  * the rate of buffer consumption. Note that buffers recycled by a
248  * strategy object are intentionally not counted here.
249  */
251 
252  /*
253  * First check, without acquiring the lock, whether there's buffers in the
254  * freelist. Since we otherwise don't require the spinlock in every
255  * StrategyGetBuffer() invocation, it'd be sad to acquire it here -
256  * uselessly in most cases. That obviously leaves a race where a buffer is
257  * put on the freelist but we don't see the store yet - but that's pretty
258  * harmless, it'll just get used during the next buffer acquisition.
259  *
260  * If there's buffers on the freelist, acquire the spinlock to pop one
261  * buffer of the freelist. Then check whether that buffer is usable and
262  * repeat if not.
263  *
264  * Note that the freeNext fields are considered to be protected by the
265  * buffer_strategy_lock not the individual buffer spinlocks, so it's OK to
266  * manipulate them without holding the spinlock.
267  */
269  {
270  while (true)
271  {
272  /* Acquire the spinlock to remove element from the freelist */
274 
276  {
278  break;
279  }
280 
282  Assert(buf->freeNext != FREENEXT_NOT_IN_LIST);
283 
284  /* Unconditionally remove buffer from freelist */
285  StrategyControl->firstFreeBuffer = buf->freeNext;
286  buf->freeNext = FREENEXT_NOT_IN_LIST;
287 
288  /*
289  * Release the lock so someone else can access the freelist while
290  * we check out this buffer.
291  */
293 
294  /*
295  * If the buffer is pinned or has a nonzero usage_count, we cannot
296  * use it; discard it and retry. (This can only happen if VACUUM
297  * put a valid buffer in the freelist and then someone else used
298  * it before we got to it. It's probably impossible altogether as
299  * of 8.3, but we'd better check anyway.)
300  */
301  local_buf_state = LockBufHdr(buf);
302  if (BUF_STATE_GET_REFCOUNT(local_buf_state) == 0
303  && BUF_STATE_GET_USAGECOUNT(local_buf_state) == 0)
304  {
305  if (strategy != NULL)
306  AddBufferToRing(strategy, buf);
307  *buf_state = local_buf_state;
308  return buf;
309  }
310  UnlockBufHdr(buf, local_buf_state);
311  }
312  }
313 
314  /* Nothing on the freelist, so run the "clock sweep" algorithm */
315  trycounter = NBuffers;
316  for (;;)
317  {
319 
320  /*
321  * If the buffer is pinned or has a nonzero usage_count, we cannot use
322  * it; decrement the usage_count (unless pinned) and keep scanning.
323  */
324  local_buf_state = LockBufHdr(buf);
325 
326  if (BUF_STATE_GET_REFCOUNT(local_buf_state) == 0)
327  {
328  if (BUF_STATE_GET_USAGECOUNT(local_buf_state) != 0)
329  {
330  local_buf_state -= BUF_USAGECOUNT_ONE;
331 
332  trycounter = NBuffers;
333  }
334  else
335  {
336  /* Found a usable buffer */
337  if (strategy != NULL)
338  AddBufferToRing(strategy, buf);
339  *buf_state = local_buf_state;
340  return buf;
341  }
342  }
343  else if (--trycounter == 0)
344  {
345  /*
346  * We've scanned all the buffers without making any state changes,
347  * so all the buffers are pinned (or were when we looked at them).
348  * We could hope that someone will free one eventually, but it's
349  * probably better to fail than to risk getting stuck in an
350  * infinite loop.
351  */
352  UnlockBufHdr(buf, local_buf_state);
353  elog(ERROR, "no unpinned buffers available");
354  }
355  UnlockBufHdr(buf, local_buf_state);
356  }
357 }
#define BUF_USAGECOUNT_ONE
Definition: buf_internals.h:45
static uint32 ClockSweepTick(void)
Definition: freelist.c:108
static void AddBufferToRing(BufferAccessStrategy strategy, BufferDesc *buf)
Definition: freelist.c:748
#define INT_ACCESS_ONCE(var)
Definition: freelist.c:24
static BufferDesc * GetBufferFromRing(BufferAccessStrategy strategy, uint32 *buf_state)
Definition: freelist.c:695
void SetLatch(Latch *latch)
Definition: latch.c:632
PROC_HDR * ProcGlobal
Definition: proc.c:78
pg_atomic_uint32 numBufferAllocs
Definition: freelist.c:55
Latch procLatch
Definition: proc.h:169
PGPROC * allProcs
Definition: proc.h:384

References AddBufferToRing(), PROC_HDR::allProcs, Assert, BufferStrategyControl::bgwprocno, buf, BUF_STATE_GET_REFCOUNT, BUF_STATE_GET_USAGECOUNT, BUF_USAGECOUNT_ONE, BufferStrategyControl::buffer_strategy_lock, ClockSweepTick(), elog, ERROR, BufferStrategyControl::firstFreeBuffer, FREENEXT_NOT_IN_LIST, GetBufferDescriptor(), GetBufferFromRing(), INT_ACCESS_ONCE, LockBufHdr(), NBuffers, BufferStrategyControl::numBufferAllocs, pg_atomic_fetch_add_u32(), ProcGlobal, PGPROC::procLatch, SetLatch(), SpinLockAcquire, SpinLockRelease, StrategyControl, and UnlockBufHdr().

Referenced by GetVictimBuffer().

◆ StrategyInitialize()

void StrategyInitialize ( bool  init)

Definition at line 474 of file freelist.c.

475 {
476  bool found;
477 
478  /*
479  * Initialize the shared buffer lookup hashtable.
480  *
481  * Since we can't tolerate running out of lookup table entries, we must be
482  * sure to specify an adequate table size here. The maximum steady-state
483  * usage is of course NBuffers entries, but BufferAlloc() tries to insert
484  * a new entry before deleting the old. In principle this could be
485  * happening in each partition concurrently, so we could need as many as
486  * NBuffers + NUM_BUFFER_PARTITIONS entries.
487  */
489 
490  /*
491  * Get or create the shared strategy control block
492  */
494  ShmemInitStruct("Buffer Strategy Status",
495  sizeof(BufferStrategyControl),
496  &found);
497 
498  if (!found)
499  {
500  /*
501  * Only done once, usually in postmaster
502  */
503  Assert(init);
504 
506 
507  /*
508  * Grab the whole linked list of free buffers for our strategy. We
509  * assume it was previously set up by BufferManagerShmemInit().
510  */
513 
514  /* Initialize the clock sweep pointer */
516 
517  /* Clear statistics */
520 
521  /* No pending notification */
523  }
524  else
525  Assert(!init);
526 }
static void pg_atomic_init_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
Definition: atomics.h:221
void InitBufTable(int size)
Definition: buf_table.c:51
int init
Definition: isn.c:74
#define NUM_BUFFER_PARTITIONS
Definition: lwlock.h:93
void * ShmemInitStruct(const char *name, Size size, bool *foundPtr)
Definition: shmem.c:387
#define SpinLockInit(lock)
Definition: spin.h:57

References Assert, BufferStrategyControl::bgwprocno, BufferStrategyControl::buffer_strategy_lock, BufferStrategyControl::completePasses, BufferStrategyControl::firstFreeBuffer, init, InitBufTable(), BufferStrategyControl::lastFreeBuffer, NBuffers, BufferStrategyControl::nextVictimBuffer, NUM_BUFFER_PARTITIONS, BufferStrategyControl::numBufferAllocs, pg_atomic_init_u32(), ShmemInitStruct(), SpinLockInit, and StrategyControl.

Referenced by BufferManagerShmemInit().

◆ StrategyNotifyBgWriter()

void StrategyNotifyBgWriter ( int  bgwprocno)

Definition at line 431 of file freelist.c.

432 {
433  /*
434  * We acquire buffer_strategy_lock just to ensure that the store appears
435  * atomic to StrategyGetBuffer. The bgwriter should call this rather
436  * infrequently, so there's no performance penalty from being safe.
437  */
439  StrategyControl->bgwprocno = bgwprocno;
441 }

References BufferStrategyControl::bgwprocno, BufferStrategyControl::buffer_strategy_lock, SpinLockAcquire, SpinLockRelease, and StrategyControl.

Referenced by BackgroundWriterMain().

◆ StrategyRejectBuffer()

bool StrategyRejectBuffer ( BufferAccessStrategy  strategy,
BufferDesc buf,
bool  from_ring 
)

Definition at line 798 of file freelist.c.

799 {
800  /* We only do this in bulkread mode */
801  if (strategy->btype != BAS_BULKREAD)
802  return false;
803 
804  /* Don't muck with behavior of normal buffer-replacement strategy */
805  if (!from_ring ||
806  strategy->buffers[strategy->current] != BufferDescriptorGetBuffer(buf))
807  return false;
808 
809  /*
810  * Remove the dirty buffer from the ring; necessary to prevent infinite
811  * loop if all ring members are dirty.
812  */
813  strategy->buffers[strategy->current] = InvalidBuffer;
814 
815  return true;
816 }

References BAS_BULKREAD, BufferAccessStrategyData::btype, buf, BufferDescriptorGetBuffer(), BufferAccessStrategyData::buffers, BufferAccessStrategyData::current, and InvalidBuffer.

Referenced by GetVictimBuffer().

◆ StrategyShmemSize()

Size StrategyShmemSize ( void  )

Definition at line 453 of file freelist.c.

454 {
455  Size size = 0;
456 
457  /* size of lookup hash table ... see comment in StrategyInitialize */
459 
460  /* size of the shared replacement strategy control block */
462 
463  return size;
464 }
Size BufTableShmemSize(int size)
Definition: buf_table.c:41
#define MAXALIGN(LEN)
Definition: c.h:816
size_t Size
Definition: c.h:610
Size add_size(Size s1, Size s2)
Definition: shmem.c:493
static pg_noinline void Size size
Definition: slab.c:607

References add_size(), BufTableShmemSize(), MAXALIGN, NBuffers, NUM_BUFFER_PARTITIONS, and size.

Referenced by BufferManagerShmemSize().

◆ StrategySyncStart()

int StrategySyncStart ( uint32 complete_passes,
uint32 num_buf_alloc 
)

Definition at line 394 of file freelist.c.

395 {
396  uint32 nextVictimBuffer;
397  int result;
398 
401  result = nextVictimBuffer % NBuffers;
402 
403  if (complete_passes)
404  {
405  *complete_passes = StrategyControl->completePasses;
406 
407  /*
408  * Additionally add the number of wraparounds that happened before
409  * completePasses could be incremented. C.f. ClockSweepTick().
410  */
411  *complete_passes += nextVictimBuffer / NBuffers;
412  }
413 
414  if (num_buf_alloc)
415  {
417  }
419  return result;
420 }
static uint32 pg_atomic_read_u32(volatile pg_atomic_uint32 *ptr)
Definition: atomics.h:239
static uint32 pg_atomic_exchange_u32(volatile pg_atomic_uint32 *ptr, uint32 newval)
Definition: atomics.h:330

References BufferStrategyControl::buffer_strategy_lock, BufferStrategyControl::completePasses, NBuffers, BufferStrategyControl::nextVictimBuffer, BufferStrategyControl::numBufferAllocs, pg_atomic_exchange_u32(), pg_atomic_read_u32(), SpinLockAcquire, SpinLockRelease, and StrategyControl.

Referenced by BgBufferSync().

Variable Documentation

◆ StrategyControl