PostgreSQL Source Code  git master
walwriter.c File Reference
#include "postgres.h"
#include <signal.h>
#include <unistd.h>
#include "access/xlog.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/auxprocess.h"
#include "postmaster/interrupt.h"
#include "postmaster/walwriter.h"
#include "storage/bufmgr.h"
#include "storage/condition_variable.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
#include "storage/proc.h"
#include "storage/procsignal.h"
#include "storage/smgr.h"
#include "utils/guc.h"
#include "utils/hsearch.h"
#include "utils/memutils.h"
#include "utils/resowner.h"
Include dependency graph for walwriter.c:

Go to the source code of this file.

Macros

#define LOOPS_UNTIL_HIBERNATE   50
 
#define HIBERNATE_FACTOR   25
 

Functions

void WalWriterMain (char *startup_data, size_t startup_data_len)
 

Variables

int WalWriterDelay = 200
 
int WalWriterFlushAfter = DEFAULT_WAL_WRITER_FLUSH_AFTER
 

Macro Definition Documentation

◆ HIBERNATE_FACTOR

#define HIBERNATE_FACTOR   25

Definition at line 80 of file walwriter.c.

◆ LOOPS_UNTIL_HIBERNATE

#define LOOPS_UNTIL_HIBERNATE   50

Definition at line 79 of file walwriter.c.

Function Documentation

◆ WalWriterMain()

void WalWriterMain ( char *  startup_data,
size_t  startup_data_len 
)

Definition at line 89 of file walwriter.c.

90 {
91  sigjmp_buf local_sigjmp_buf;
92  MemoryContext walwriter_context;
93  int left_till_hibernate;
94  bool hibernating;
95 
96  Assert(startup_data_len == 0);
97 
100 
101  /*
102  * Properly accept or ignore signals the postmaster might send us
103  *
104  * We have no particular use for SIGINT at the moment, but seems
105  * reasonable to treat like SIGTERM.
106  */
110  /* SIGQUIT handler was already set up by InitPostmasterChild */
114  pqsignal(SIGUSR2, SIG_IGN); /* not used */
115 
116  /*
117  * Reset some signals that are accepted by postmaster but not here
118  */
120 
121  /*
122  * Create a memory context that we will do all our work in. We do this so
123  * that we can reset the context during error recovery and thereby avoid
124  * possible memory leaks. Formerly this code just ran in
125  * TopMemoryContext, but resetting that would be a really bad idea.
126  */
127  walwriter_context = AllocSetContextCreate(TopMemoryContext,
128  "Wal Writer",
130  MemoryContextSwitchTo(walwriter_context);
131 
132  /*
133  * If an exception is encountered, processing resumes here.
134  *
135  * You might wonder why this isn't coded as an infinite loop around a
136  * PG_TRY construct. The reason is that this is the bottom of the
137  * exception stack, and so with PG_TRY there would be no exception handler
138  * in force at all during the CATCH part. By leaving the outermost setjmp
139  * always active, we have at least some chance of recovering from an error
140  * during error recovery. (If we get into an infinite loop thereby, it
141  * will soon be stopped by overflow of elog.c's internal state stack.)
142  *
143  * Note that we use sigsetjmp(..., 1), so that the prevailing signal mask
144  * (to wit, BlockSig) will be restored when longjmp'ing to here. Thus,
145  * signals other than SIGQUIT will be blocked until we complete error
146  * recovery. It might seem that this policy makes the HOLD_INTERRUPTS()
147  * call redundant, but it is not since InterruptPending might be set
148  * already.
149  */
150  if (sigsetjmp(local_sigjmp_buf, 1) != 0)
151  {
152  /* Since not using PG_TRY, must reset error stack by hand */
153  error_context_stack = NULL;
154 
155  /* Prevent interrupts while cleaning up */
156  HOLD_INTERRUPTS();
157 
158  /* Report the error to the server log */
159  EmitErrorReport();
160 
161  /*
162  * These operations are really just a minimal subset of
163  * AbortTransaction(). We don't have very many resources to worry
164  * about in walwriter, but we do have LWLocks, and perhaps buffers?
165  */
169  UnlockBuffers();
171  AtEOXact_Buffers(false);
172  AtEOXact_SMgr();
173  AtEOXact_Files(false);
174  AtEOXact_HashTables(false);
175 
176  /*
177  * Now return to normal top-level context and clear ErrorContext for
178  * next time.
179  */
180  MemoryContextSwitchTo(walwriter_context);
181  FlushErrorState();
182 
183  /* Flush any leaked data in the top-level context */
184  MemoryContextReset(walwriter_context);
185 
186  /* Now we can allow interrupts again */
188 
189  /*
190  * Sleep at least 1 second after any error. A write error is likely
191  * to be repeated, and we don't want to be filling the error logs as
192  * fast as we can.
193  */
194  pg_usleep(1000000L);
195  }
196 
197  /* We can now handle ereport(ERROR) */
198  PG_exception_stack = &local_sigjmp_buf;
199 
200  /*
201  * Unblock signals (they were blocked when the postmaster forked us)
202  */
203  sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
204 
205  /*
206  * Reset hibernation state after any error.
207  */
208  left_till_hibernate = LOOPS_UNTIL_HIBERNATE;
209  hibernating = false;
210  SetWalWriterSleeping(false);
211 
212  /*
213  * Advertise our latch that backends can use to wake us up while we're
214  * sleeping.
215  */
217 
218  /*
219  * Loop forever
220  */
221  for (;;)
222  {
223  long cur_timeout;
224 
225  /*
226  * Advertise whether we might hibernate in this cycle. We do this
227  * before resetting the latch to ensure that any async commits will
228  * see the flag set if they might possibly need to wake us up, and
229  * that we won't miss any signal they send us. (If we discover work
230  * to do in the last cycle before we would hibernate, the global flag
231  * will be set unnecessarily, but little harm is done.) But avoid
232  * touching the global flag if it doesn't need to change.
233  */
234  if (hibernating != (left_till_hibernate <= 1))
235  {
236  hibernating = (left_till_hibernate <= 1);
237  SetWalWriterSleeping(hibernating);
238  }
239 
240  /* Clear any already-pending wakeups */
242 
243  /* Process any signals received recently */
245 
246  /*
247  * Do what we're here for; then, if XLogBackgroundFlush() found useful
248  * work to do, reset hibernation counter.
249  */
250  if (XLogBackgroundFlush())
251  left_till_hibernate = LOOPS_UNTIL_HIBERNATE;
252  else if (left_till_hibernate > 0)
253  left_till_hibernate--;
254 
255  /* report pending statistics to the cumulative stats system */
256  pgstat_report_wal(false);
257 
258  /*
259  * Sleep until we are signaled or WalWriterDelay has elapsed. If we
260  * haven't done anything useful for quite some time, lengthen the
261  * sleep time so as to reduce the server's idle power consumption.
262  */
263  if (left_till_hibernate > 0)
264  cur_timeout = WalWriterDelay; /* in ms */
265  else
266  cur_timeout = WalWriterDelay * HIBERNATE_FACTOR;
267 
268  (void) WaitLatch(MyLatch,
270  cur_timeout,
271  WAIT_EVENT_WAL_WRITER_MAIN);
272  }
273 }
void AuxiliaryProcessMainCommon(void)
Definition: auxprocess.c:44
sigset_t UnBlockSig
Definition: pqsignal.c:22
void AtEOXact_Buffers(bool isCommit)
Definition: bufmgr.c:3548
void UnlockBuffers(void)
Definition: bufmgr.c:5103
#define Assert(condition)
Definition: c.h:858
bool ConditionVariableCancelSleep(void)
void AtEOXact_HashTables(bool isCommit)
Definition: dynahash.c:1869
void EmitErrorReport(void)
Definition: elog.c:1670
ErrorContextCallback * error_context_stack
Definition: elog.c:94
void FlushErrorState(void)
Definition: elog.c:1834
sigjmp_buf * PG_exception_stack
Definition: elog.c:96
void AtEOXact_Files(bool isCommit)
Definition: fd.c:3165
struct Latch * MyLatch
Definition: globals.c:60
void SignalHandlerForShutdownRequest(SIGNAL_ARGS)
Definition: interrupt.c:105
void SignalHandlerForConfigReload(SIGNAL_ARGS)
Definition: interrupt.c:61
void HandleMainLoopInterrupts(void)
Definition: interrupt.c:34
void ResetLatch(Latch *latch)
Definition: latch.c:724
int WaitLatch(Latch *latch, int wakeEvents, long timeout, uint32 wait_event_info)
Definition: latch.c:517
#define WL_TIMEOUT
Definition: latch.h:130
#define WL_EXIT_ON_PM_DEATH
Definition: latch.h:132
#define WL_LATCH_SET
Definition: latch.h:127
void LWLockReleaseAll(void)
Definition: lwlock.c:1878
void MemoryContextReset(MemoryContext context)
Definition: mcxt.c:383
MemoryContext TopMemoryContext
Definition: mcxt.c:149
#define AllocSetContextCreate
Definition: memutils.h:129
#define ALLOCSET_DEFAULT_SIZES
Definition: memutils.h:160
#define RESUME_INTERRUPTS()
Definition: miscadmin.h:135
#define HOLD_INTERRUPTS()
Definition: miscadmin.h:133
@ B_WAL_WRITER
Definition: miscadmin.h:361
BackendType MyBackendType
Definition: miscinit.c:63
void pgstat_report_wal(bool force)
Definition: pgstat_wal.c:48
pqsigfunc pqsignal(int signo, pqsigfunc func)
void procsignal_sigusr1_handler(SIGNAL_ARGS)
Definition: procsignal.c:635
MemoryContextSwitchTo(old_ctx)
void ReleaseAuxProcessResources(bool isCommit)
Definition: resowner.c:1002
void pg_usleep(long microsec)
Definition: signal.c:53
void AtEOXact_SMgr(void)
Definition: smgr.c:807
PGPROC * MyProc
Definition: proc.c:66
PROC_HDR * ProcGlobal
Definition: proc.c:78
Latch procLatch
Definition: proc.h:165
Latch * walwriterLatch
Definition: proc.h:412
static void pgstat_report_wait_end(void)
Definition: wait_event.h:98
#define HIBERNATE_FACTOR
Definition: walwriter.c:80
#define LOOPS_UNTIL_HIBERNATE
Definition: walwriter.c:79
int WalWriterDelay
Definition: walwriter.c:71
#define SIGCHLD
Definition: win32_port.h:178
#define SIGHUP
Definition: win32_port.h:168
#define SIG_DFL
Definition: win32_port.h:163
#define SIGPIPE
Definition: win32_port.h:173
#define SIGUSR1
Definition: win32_port.h:180
#define SIGALRM
Definition: win32_port.h:174
#define SIGUSR2
Definition: win32_port.h:181
#define SIG_IGN
Definition: win32_port.h:165
void SetWalWriterSleeping(bool sleeping)
Definition: xlog.c:9427
bool XLogBackgroundFlush(void)
Definition: xlog.c:2979

References ALLOCSET_DEFAULT_SIZES, AllocSetContextCreate, Assert, AtEOXact_Buffers(), AtEOXact_Files(), AtEOXact_HashTables(), AtEOXact_SMgr(), AuxiliaryProcessMainCommon(), B_WAL_WRITER, ConditionVariableCancelSleep(), EmitErrorReport(), error_context_stack, FlushErrorState(), HandleMainLoopInterrupts(), HIBERNATE_FACTOR, HOLD_INTERRUPTS, LOOPS_UNTIL_HIBERNATE, LWLockReleaseAll(), MemoryContextReset(), MemoryContextSwitchTo(), MyBackendType, MyLatch, MyProc, PG_exception_stack, pg_usleep(), pgstat_report_wait_end(), pgstat_report_wal(), pqsignal(), ProcGlobal, PGPROC::procLatch, procsignal_sigusr1_handler(), ReleaseAuxProcessResources(), ResetLatch(), RESUME_INTERRUPTS, SetWalWriterSleeping(), SIG_DFL, SIG_IGN, SIGALRM, SIGCHLD, SIGHUP, SignalHandlerForConfigReload(), SignalHandlerForShutdownRequest(), SIGPIPE, SIGUSR1, SIGUSR2, TopMemoryContext, UnBlockSig, UnlockBuffers(), WaitLatch(), WalWriterDelay, PROC_HDR::walwriterLatch, WL_EXIT_ON_PM_DEATH, WL_LATCH_SET, WL_TIMEOUT, and XLogBackgroundFlush().

Variable Documentation

◆ WalWriterDelay

int WalWriterDelay = 200

Definition at line 71 of file walwriter.c.

Referenced by LogicalRepApplyLoop(), WalWriterMain(), and XLogBackgroundFlush().

◆ WalWriterFlushAfter

int WalWriterFlushAfter = DEFAULT_WAL_WRITER_FLUSH_AFTER

Definition at line 72 of file walwriter.c.

Referenced by XLogBackgroundFlush(), and XLogSetAsyncXactLSN().