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/*-------------------------------------------------------------------------
*
* checkpointer.c
*
* The checkpointer is new as of Postgres 9.2. It handles all checkpoints.
* Checkpoints are automatically dispatched after a certain amount of time has
* elapsed since the last one, and it can be signaled to perform requested
* checkpoints as well. (The GUC parameter that mandates a checkpoint every
* so many WAL segments is implemented by having backends signal when they
* fill WAL segments; the checkpointer itself doesn't watch for the
* condition.)
*
* The checkpointer is started by the postmaster as soon as the startup subprocess
* finishes, or as soon as recovery begins if we are doing archive recovery.
* It remains alive until the postmaster commands it to terminate.
* Normal termination is by SIGUSR2, which instructs the checkpointer to execute
* a shutdown checkpoint and then exit(0). (All backends must be stopped
* before SIGUSR2 is issued!) Emergency termination is by SIGQUIT; like any
* backend, the checkpointer will simply abort and exit on SIGQUIT.
*
* If the checkpointer exits unexpectedly, the postmaster treats that the same
* as a backend crash: shared memory may be corrupted, so remaining backends
* should be killed by SIGQUIT and then a recovery cycle started. (Even if
* shared memory isn't corrupted, we have lost information about which
* files need to be fsync'd for the next checkpoint, and so a system
* restart needs to be forced.)
*
*
* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
*
*
* IDENTIFICATION
* src/backend/postmaster/checkpointer.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <signal.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include "access/xlog_internal.h"
#include "libpq/pqsignal.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/bgwriter.h"
#include "replication/syncrep.h"
#include "storage/bufmgr.h"
#include "storage/ipc.h"
#include "storage/lwlock.h"
#include "storage/pmsignal.h"
#include "storage/shmem.h"
#include "storage/smgr.h"
#include "storage/spin.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/resowner.h"
/*----------
* Shared memory area for communication between checkpointer and backends
*
* The ckpt counters allow backends to watch for completion of a checkpoint
* request they send. Here's how it works:
* * At start of a checkpoint, checkpointer reads (and clears) the request flags
* and increments ckpt_started, while holding ckpt_lck.
* * On completion of a checkpoint, checkpointer sets ckpt_done to
* equal ckpt_started.
* * On failure of a checkpoint, checkpointer increments ckpt_failed
* and sets ckpt_done to equal ckpt_started.
*
* The algorithm for backends is:
* 1. Record current values of ckpt_failed and ckpt_started, and
* set request flags, while holding ckpt_lck.
* 2. Send signal to request checkpoint.
* 3. Sleep until ckpt_started changes. Now you know a checkpoint has
* begun since you started this algorithm (although *not* that it was
* specifically initiated by your signal), and that it is using your flags.
* 4. Record new value of ckpt_started.
* 5. Sleep until ckpt_done >= saved value of ckpt_started. (Use modulo
* arithmetic here in case counters wrap around.) Now you know a
* checkpoint has started and completed, but not whether it was
* successful.
* 6. If ckpt_failed is different from the originally saved value,
* assume request failed; otherwise it was definitely successful.
*
* ckpt_flags holds the OR of the checkpoint request flags sent by all
* requesting backends since the last checkpoint start. The flags are
* chosen so that OR'ing is the correct way to combine multiple requests.
*
* num_backend_writes is used to count the number of buffer writes performed
* by user backend processes. This counter should be wide enough that it
* can't overflow during a single processing cycle. num_backend_fsync
* counts the subset of those writes that also had to do their own fsync,
* because the background writer failed to absorb their request.
*
* The requests array holds fsync requests sent by backends and not yet
* absorbed by the checkpointer.
*
* Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
* the requests fields are protected by BgWriterCommLock.
*----------
*/
typedef struct
{
RelFileNodeBackend rnode;
ForkNumber forknum;
BlockNumber segno; /* see md.c for special values */
/* might add a real request-type field later; not needed yet */
} BgWriterRequest;
typedef struct
{
pid_t checkpointer_pid; /* PID (0 if not started) */
slock_t ckpt_lck; /* protects all the ckpt_* fields */
int ckpt_started; /* advances when checkpoint starts */
int ckpt_done; /* advances when checkpoint done */
int ckpt_failed; /* advances when checkpoint fails */
int ckpt_flags; /* checkpoint flags, as defined in xlog.h */
uint32 num_backend_writes; /* counts user backend buffer writes */
uint32 num_backend_fsync; /* counts user backend fsync calls */
int num_requests; /* current # of requests */
int max_requests; /* allocated array size */
BgWriterRequest requests[1]; /* VARIABLE LENGTH ARRAY */
} BgWriterShmemStruct;
static BgWriterShmemStruct *BgWriterShmem;
/* interval for calling AbsorbFsyncRequests in CheckpointWriteDelay */
#define WRITES_PER_ABSORB 1000
/*
* GUC parameters
*/
int CheckPointTimeout = 300;
int CheckPointWarning = 30;
double CheckPointCompletionTarget = 0.5;
/*
* Flags set by interrupt handlers for later service in the main loop.
*/
static volatile sig_atomic_t got_SIGHUP = false;
static volatile sig_atomic_t checkpoint_requested = false;
static volatile sig_atomic_t shutdown_requested = false;
/*
* Private state
*/
static bool am_checkpointer = false;
static bool ckpt_active = false;
/* these values are valid when ckpt_active is true: */
static pg_time_t ckpt_start_time;
static XLogRecPtr ckpt_start_recptr;
static double ckpt_cached_elapsed;
static pg_time_t last_checkpoint_time;
static pg_time_t last_xlog_switch_time;
/* Prototypes for private functions */
static void CheckArchiveTimeout(void);
static bool IsCheckpointOnSchedule(double progress);
static bool ImmediateCheckpointRequested(void);
static bool CompactCheckpointerRequestQueue(void);
static void UpdateSharedMemoryConfig(void);
/* Signal handlers */
static void chkpt_quickdie(SIGNAL_ARGS);
static void ChkptSigHupHandler(SIGNAL_ARGS);
static void ReqCheckpointHandler(SIGNAL_ARGS);
static void ReqShutdownHandler(SIGNAL_ARGS);
/*
* Main entry point for checkpointer process
*
* This is invoked from BootstrapMain, which has already created the basic
* execution environment, but not enabled signals yet.
*/
void
CheckpointerMain(void)
{
sigjmp_buf local_sigjmp_buf;
MemoryContext checkpointer_context;
BgWriterShmem->checkpointer_pid = MyProcPid;
am_checkpointer = true;
/*
* If possible, make this process a group leader, so that the postmaster
* can signal any child processes too. (checkpointer probably never has any
* child processes, but for consistency we make all postmaster child
* processes do this.)
*/
#ifdef HAVE_SETSID
if (setsid() < 0)
elog(FATAL, "setsid() failed: %m");
#endif
/*
* Properly accept or ignore signals the postmaster might send us
*
* Note: we deliberately ignore SIGTERM, because during a standard Unix
* system shutdown cycle, init will SIGTERM all processes at once. We
* want to wait for the backends to exit, whereupon the postmaster will
* tell us it's okay to shut down (via SIGUSR2).
*
* SIGUSR1 is presently unused; keep it spare in case someday we want this
* process to participate in ProcSignal signalling.
*/
pqsignal(SIGHUP, ChkptSigHupHandler); /* set flag to read config file */
pqsignal(SIGINT, ReqCheckpointHandler); /* request checkpoint */
pqsignal(SIGTERM, SIG_IGN); /* ignore SIGTERM */
pqsignal(SIGQUIT, chkpt_quickdie); /* hard crash time */
pqsignal(SIGALRM, SIG_IGN);
pqsignal(SIGPIPE, SIG_IGN);
pqsignal(SIGUSR1, SIG_IGN); /* reserve for ProcSignal */
pqsignal(SIGUSR2, ReqShutdownHandler); /* request shutdown */
/*
* Reset some signals that are accepted by postmaster but not here
*/
pqsignal(SIGCHLD, SIG_DFL);
pqsignal(SIGTTIN, SIG_DFL);
pqsignal(SIGTTOU, SIG_DFL);
pqsignal(SIGCONT, SIG_DFL);
pqsignal(SIGWINCH, SIG_DFL);
/* We allow SIGQUIT (quickdie) at all times */
sigdelset(&BlockSig, SIGQUIT);
/*
* Initialize so that first time-driven event happens at the correct time.
*/
last_checkpoint_time = last_xlog_switch_time = (pg_time_t) time(NULL);
/*
* Create a resource owner to keep track of our resources (currently only
* buffer pins).
*/
CurrentResourceOwner = ResourceOwnerCreate(NULL, "Checkpointer");
/*
* Create a memory context that we will do all our work in. We do this so
* that we can reset the context during error recovery and thereby avoid
* possible memory leaks. Formerly this code just ran in
* TopMemoryContext, but resetting that would be a really bad idea.
*/
checkpointer_context = AllocSetContextCreate(TopMemoryContext,
"Checkpointer",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
MemoryContextSwitchTo(checkpointer_context);
/*
* If an exception is encountered, processing resumes here.
*
* See notes in postgres.c about the design of this coding.
*/
if (sigsetjmp(local_sigjmp_buf, 1) != 0)
{
/* Since not using PG_TRY, must reset error stack by hand */
error_context_stack = NULL;
/* Prevent interrupts while cleaning up */
HOLD_INTERRUPTS();
/* Report the error to the server log */
EmitErrorReport();
/*
* These operations are really just a minimal subset of
* AbortTransaction(). We don't have very many resources to worry
* about in checkpointer, but we do have LWLocks, buffers, and temp files.
*/
LWLockReleaseAll();
AbortBufferIO();
UnlockBuffers();
/* buffer pins are released here: */
ResourceOwnerRelease(CurrentResourceOwner,
RESOURCE_RELEASE_BEFORE_LOCKS,
false, true);
/* we needn't bother with the other ResourceOwnerRelease phases */
AtEOXact_Buffers(false);
AtEOXact_Files();
AtEOXact_HashTables(false);
/* Warn any waiting backends that the checkpoint failed. */
if (ckpt_active)
{
/* use volatile pointer to prevent code rearrangement */
volatile BgWriterShmemStruct *bgs = BgWriterShmem;
SpinLockAcquire(&bgs->ckpt_lck);
bgs->ckpt_failed++;
bgs->ckpt_done = bgs->ckpt_started;
SpinLockRelease(&bgs->ckpt_lck);
ckpt_active = false;
}
/*
* Now return to normal top-level context and clear ErrorContext for
* next time.
*/
MemoryContextSwitchTo(checkpointer_context);
FlushErrorState();
/* Flush any leaked data in the top-level context */
MemoryContextResetAndDeleteChildren(checkpointer_context);
/* Now we can allow interrupts again */
RESUME_INTERRUPTS();
/*
* Sleep at least 1 second after any error. A write error is likely
* to be repeated, and we don't want to be filling the error logs as
* fast as we can.
*/
pg_usleep(1000000L);
/*
* Close all open files after any error. This is helpful on Windows,
* where holding deleted files open causes various strange errors.
* It's not clear we need it elsewhere, but shouldn't hurt.
*/
smgrcloseall();
}
/* We can now handle ereport(ERROR) */
PG_exception_stack = &local_sigjmp_buf;
/*
* Unblock signals (they were blocked when the postmaster forked us)
*/
PG_SETMASK(&UnBlockSig);
/*
* Use the recovery target timeline ID during recovery
*/
if (RecoveryInProgress())
ThisTimeLineID = GetRecoveryTargetTLI();
/*
* Ensure all shared memory values are set correctly for the config.
* Doing this here ensures no race conditions from other concurrent
* updaters.
*/
UpdateSharedMemoryConfig();
/*
* Loop forever
*/
for (;;)
{
bool do_checkpoint = false;
int flags = 0;
pg_time_t now;
int elapsed_secs;
/*
* Emergency bailout if postmaster has died. This is to avoid the
* necessity for manual cleanup of all postmaster children.
*/
if (!PostmasterIsAlive())
exit(1);
/*
* Process any requests or signals received recently.
*/
AbsorbFsyncRequests();
if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
/*
* Checkpointer is the last process to shutdown, so we ask
* it to hold the keys for a range of other tasks required
* most of which have nothing to do with checkpointing at all.
*
* For various reasons, some config values can change
* dynamically so are the primary copy of them is held in
* shared memory to make sure all backends see the same value.
* We make Checkpointer responsible for updating the shared
* memory copy if the parameter setting changes because of SIGHUP.
*/
UpdateSharedMemoryConfig();
}
if (checkpoint_requested)
{
checkpoint_requested = false;
do_checkpoint = true;
BgWriterStats.m_requested_checkpoints++;
}
if (shutdown_requested)
{
/*
* From here on, elog(ERROR) should end with exit(1), not send
* control back to the sigsetjmp block above
*/
ExitOnAnyError = true;
/* Close down the database */
ShutdownXLOG(0, 0);
/* Normal exit from the checkpointer is here */
proc_exit(0); /* done */
}
/*
* Force a checkpoint if too much time has elapsed since the last one.
* Note that we count a timed checkpoint in stats only when this
* occurs without an external request, but we set the CAUSE_TIME flag
* bit even if there is also an external request.
*/
now = (pg_time_t) time(NULL);
elapsed_secs = now - last_checkpoint_time;
if (elapsed_secs >= CheckPointTimeout)
{
if (!do_checkpoint)
BgWriterStats.m_timed_checkpoints++;
do_checkpoint = true;
flags |= CHECKPOINT_CAUSE_TIME;
}
/*
* Do a checkpoint if requested.
*/
if (do_checkpoint)
{
bool ckpt_performed = false;
bool do_restartpoint;
/* use volatile pointer to prevent code rearrangement */
volatile BgWriterShmemStruct *bgs = BgWriterShmem;
/*
* Check if we should perform a checkpoint or a restartpoint. As a
* side-effect, RecoveryInProgress() initializes TimeLineID if
* it's not set yet.
*/
do_restartpoint = RecoveryInProgress();
/*
* Atomically fetch the request flags to figure out what kind of a
* checkpoint we should perform, and increase the started-counter
* to acknowledge that we've started a new checkpoint.
*/
SpinLockAcquire(&bgs->ckpt_lck);
flags |= bgs->ckpt_flags;
bgs->ckpt_flags = 0;
bgs->ckpt_started++;
SpinLockRelease(&bgs->ckpt_lck);
/*
* The end-of-recovery checkpoint is a real checkpoint that's
* performed while we're still in recovery.
*/
if (flags & CHECKPOINT_END_OF_RECOVERY)
do_restartpoint = false;
/*
* We will warn if (a) too soon since last checkpoint (whatever
* caused it) and (b) somebody set the CHECKPOINT_CAUSE_XLOG flag
* since the last checkpoint start. Note in particular that this
* implementation will not generate warnings caused by
* CheckPointTimeout < CheckPointWarning.
*/
if (!do_restartpoint &&
(flags & CHECKPOINT_CAUSE_XLOG) &&
elapsed_secs < CheckPointWarning)
ereport(LOG,
(errmsg_plural("checkpoints are occurring too frequently (%d second apart)",
"checkpoints are occurring too frequently (%d seconds apart)",
elapsed_secs,
elapsed_secs),
errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));
/*
* Initialize checkpointer-private variables used during checkpoint.
*/
ckpt_active = true;
if (!do_restartpoint)
ckpt_start_recptr = GetInsertRecPtr();
ckpt_start_time = now;
ckpt_cached_elapsed = 0;
/*
* Do the checkpoint.
*/
if (!do_restartpoint)
{
CreateCheckPoint(flags);
ckpt_performed = true;
}
else
ckpt_performed = CreateRestartPoint(flags);
/*
* After any checkpoint, close all smgr files. This is so we
* won't hang onto smgr references to deleted files indefinitely.
*/
smgrcloseall();
/*
* Indicate checkpoint completion to any waiting backends.
*/
SpinLockAcquire(&bgs->ckpt_lck);
bgs->ckpt_done = bgs->ckpt_started;
SpinLockRelease(&bgs->ckpt_lck);
if (ckpt_performed)
{
/*
* Note we record the checkpoint start time not end time as
* last_checkpoint_time. This is so that time-driven
* checkpoints happen at a predictable spacing.
*/
last_checkpoint_time = now;
}
else
{
/*
* We were not able to perform the restartpoint (checkpoints
* throw an ERROR in case of error). Most likely because we
* have not received any new checkpoint WAL records since the
* last restartpoint. Try again in 15 s.
*/
last_checkpoint_time = now - CheckPointTimeout + 15;
}
ckpt_active = false;
}
/*
* Send off activity statistics to the stats collector
*/
pgstat_send_bgwriter();
/*
* Nap for a while and then loop again. Later patches will replace
* this with a latch loop. Keep it simple now for clarity.
* Relatively long sleep because the bgwriter does cleanup now.
*/
pg_usleep(500000L);
/* Check for archive_timeout and switch xlog files if necessary. */
CheckArchiveTimeout();
}
}
/*
* CheckArchiveTimeout -- check for archive_timeout and switch xlog files
*
* This will switch to a new WAL file and force an archive file write
* if any activity is recorded in the current WAL file, including just
* a single checkpoint record.
*/
static void
CheckArchiveTimeout(void)
{
pg_time_t now;
pg_time_t last_time;
if (XLogArchiveTimeout <= 0 || RecoveryInProgress())
return;
now = (pg_time_t) time(NULL);
/* First we do a quick check using possibly-stale local state. */
if ((int) (now - last_xlog_switch_time) < XLogArchiveTimeout)
return;
/*
* Update local state ... note that last_xlog_switch_time is the last time
* a switch was performed *or requested*.
*/
last_time = GetLastSegSwitchTime();
last_xlog_switch_time = Max(last_xlog_switch_time, last_time);
/* Now we can do the real check */
if ((int) (now - last_xlog_switch_time) >= XLogArchiveTimeout)
{
XLogRecPtr switchpoint;
/* OK, it's time to switch */
switchpoint = RequestXLogSwitch();
/*
* If the returned pointer points exactly to a segment boundary,
* assume nothing happened.
*/
if ((switchpoint.xrecoff % XLogSegSize) != 0)
ereport(DEBUG1,
(errmsg("transaction log switch forced (archive_timeout=%d)",
XLogArchiveTimeout)));
/*
* Update state in any case, so we don't retry constantly when the
* system is idle.
*/
last_xlog_switch_time = now;
}
}
/*
* Returns true if an immediate checkpoint request is pending. (Note that
* this does not check the *current* checkpoint's IMMEDIATE flag, but whether
* there is one pending behind it.)
*/
static bool
ImmediateCheckpointRequested(void)
{
if (checkpoint_requested)
{
volatile BgWriterShmemStruct *bgs = BgWriterShmem;
/*
* We don't need to acquire the ckpt_lck in this case because we're
* only looking at a single flag bit.
*/
if (bgs->ckpt_flags & CHECKPOINT_IMMEDIATE)
return true;
}
return false;
}
/*
* CheckpointWriteDelay -- control rate of checkpoint
*
* This function is called after each page write performed by BufferSync().
* It is responsible for throttling BufferSync()'s write rate to hit
* checkpoint_completion_target.
*
* The checkpoint request flags should be passed in; currently the only one
* examined is CHECKPOINT_IMMEDIATE, which disables delays between writes.
*
* 'progress' is an estimate of how much of the work has been done, as a
* fraction between 0.0 meaning none, and 1.0 meaning all done.
*/
void
CheckpointWriteDelay(int flags, double progress)
{
static int absorb_counter = WRITES_PER_ABSORB;
/* Do nothing if checkpoint is being executed by non-checkpointer process */
if (!am_checkpointer)
return;
/*
* Perform the usual duties and take a nap, unless we're behind
* schedule, in which case we just try to catch up as quickly as possible.
*/
if (!(flags & CHECKPOINT_IMMEDIATE) &&
!shutdown_requested &&
!ImmediateCheckpointRequested() &&
IsCheckpointOnSchedule(progress))
{
if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
/* update global shmem state for sync rep */
UpdateSharedMemoryConfig();
}
AbsorbFsyncRequests();
absorb_counter = WRITES_PER_ABSORB;
CheckArchiveTimeout();
/*
* Checkpoint sleep used to be connected to bgwriter_delay at 200ms.
* That resulted in more frequent wakeups if not much work to do.
* Checkpointer and bgwriter are no longer related so take the Big Sleep.
*/
pg_usleep(100000L);
}
else if (--absorb_counter <= 0)
{
/*
* Absorb pending fsync requests after each WRITES_PER_ABSORB write
* operations even when we don't sleep, to prevent overflow of the
* fsync request queue.
*/
AbsorbFsyncRequests();
absorb_counter = WRITES_PER_ABSORB;
}
}
/*
* IsCheckpointOnSchedule -- are we on schedule to finish this checkpoint
* in time?
*
* Compares the current progress against the time/segments elapsed since last
* checkpoint, and returns true if the progress we've made this far is greater
* than the elapsed time/segments.
*/
static bool
IsCheckpointOnSchedule(double progress)
{
XLogRecPtr recptr;
struct timeval now;
double elapsed_xlogs,
elapsed_time;
Assert(ckpt_active);
/* Scale progress according to checkpoint_completion_target. */
progress *= CheckPointCompletionTarget;
/*
* Check against the cached value first. Only do the more expensive
* calculations once we reach the target previously calculated. Since
* neither time or WAL insert pointer moves backwards, a freshly
* calculated value can only be greater than or equal to the cached value.
*/
if (progress < ckpt_cached_elapsed)
return false;
/*
* Check progress against WAL segments written and checkpoint_segments.
*
* We compare the current WAL insert location against the location
* computed before calling CreateCheckPoint. The code in XLogInsert that
* actually triggers a checkpoint when checkpoint_segments is exceeded
* compares against RedoRecptr, so this is not completely accurate.
* However, it's good enough for our purposes, we're only calculating an
* estimate anyway.
*/
if (!RecoveryInProgress())
{
recptr = GetInsertRecPtr();
elapsed_xlogs =
(((double) (int32) (recptr.xlogid - ckpt_start_recptr.xlogid)) * XLogSegsPerFile +
((double) recptr.xrecoff - (double) ckpt_start_recptr.xrecoff) / XLogSegSize) /
CheckPointSegments;
if (progress < elapsed_xlogs)
{
ckpt_cached_elapsed = elapsed_xlogs;
return false;
}
}
/*
* Check progress against time elapsed and checkpoint_timeout.
*/
gettimeofday(&now, NULL);
elapsed_time = ((double) ((pg_time_t) now.tv_sec - ckpt_start_time) +
now.tv_usec / 1000000.0) / CheckPointTimeout;
if (progress < elapsed_time)
{
ckpt_cached_elapsed = elapsed_time;
return false;
}
/* It looks like we're on schedule. */
return true;
}
/* --------------------------------
* signal handler routines
* --------------------------------
*/
/*
* chkpt_quickdie() occurs when signalled SIGQUIT by the postmaster.
*
* Some backend has bought the farm,
* so we need to stop what we're doing and exit.
*/
static void
chkpt_quickdie(SIGNAL_ARGS)
{
PG_SETMASK(&BlockSig);
/*
* We DO NOT want to run proc_exit() callbacks -- we're here because
* shared memory may be corrupted, so we don't want to try to clean up our
* transaction. Just nail the windows shut and get out of town. Now that
* there's an atexit callback to prevent third-party code from breaking
* things by calling exit() directly, we have to reset the callbacks
* explicitly to make this work as intended.
*/
on_exit_reset();
/*
* Note we do exit(2) not exit(0). This is to force the postmaster into a
* system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
* backend. This is necessary precisely because we don't clean up our
* shared memory state. (The "dead man switch" mechanism in pmsignal.c
* should ensure the postmaster sees this as a crash, too, but no harm in
* being doubly sure.)
*/
exit(2);
}
/* SIGHUP: set flag to re-read config file at next convenient time */
static void
ChkptSigHupHandler(SIGNAL_ARGS)
{
got_SIGHUP = true;
}
/* SIGINT: set flag to run a normal checkpoint right away */
static void
ReqCheckpointHandler(SIGNAL_ARGS)
{
checkpoint_requested = true;
}
/* SIGUSR2: set flag to run a shutdown checkpoint and exit */
static void
ReqShutdownHandler(SIGNAL_ARGS)
{
shutdown_requested = true;
}
/* --------------------------------
* communication with backends
* --------------------------------
*/
/*
* BgWriterShmemSize
* Compute space needed for bgwriter-related shared memory
*/
Size
BgWriterShmemSize(void)
{
Size size;
/*
* Currently, the size of the requests[] array is arbitrarily set equal to
* NBuffers. This may prove too large or small ...
*/
size = offsetof(BgWriterShmemStruct, requests);
size = add_size(size, mul_size(NBuffers, sizeof(BgWriterRequest)));
return size;
}
/*
* BgWriterShmemInit
* Allocate and initialize bgwriter-related shared memory
*/
void
BgWriterShmemInit(void)
{
bool found;
BgWriterShmem = (BgWriterShmemStruct *)
ShmemInitStruct("Background Writer Data",
BgWriterShmemSize(),
&found);
if (!found)
{
/* First time through, so initialize */
MemSet(BgWriterShmem, 0, sizeof(BgWriterShmemStruct));
SpinLockInit(&BgWriterShmem->ckpt_lck);
BgWriterShmem->max_requests = NBuffers;
}
}
/*
* RequestCheckpoint
* Called in backend processes to request a checkpoint
*
* flags is a bitwise OR of the following:
* CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
* CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
* CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
* ignoring checkpoint_completion_target parameter.
* CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occurred
* since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
* CHECKPOINT_END_OF_RECOVERY).
* CHECKPOINT_WAIT: wait for completion before returning (otherwise,
* just signal checkpointer to do it, and return).
* CHECKPOINT_CAUSE_XLOG: checkpoint is requested due to xlog filling.
* (This affects logging, and in particular enables CheckPointWarning.)
*/
void
RequestCheckpoint(int flags)
{
/* use volatile pointer to prevent code rearrangement */
volatile BgWriterShmemStruct *bgs = BgWriterShmem;
int ntries;
int old_failed,
old_started;
/*
* If in a standalone backend, just do it ourselves.
*/
if (!IsPostmasterEnvironment)
{
/*
* There's no point in doing slow checkpoints in a standalone backend,
* because there's no other backends the checkpoint could disrupt.
*/
CreateCheckPoint(flags | CHECKPOINT_IMMEDIATE);
/*
* After any checkpoint, close all smgr files. This is so we won't
* hang onto smgr references to deleted files indefinitely.
*/
smgrcloseall();
return;
}
/*
* Atomically set the request flags, and take a snapshot of the counters.
* When we see ckpt_started > old_started, we know the flags we set here
* have been seen by checkpointer.
*
* Note that we OR the flags with any existing flags, to avoid overriding
* a "stronger" request by another backend. The flag senses must be
* chosen to make this work!
*/
SpinLockAcquire(&bgs->ckpt_lck);
old_failed = bgs->ckpt_failed;
old_started = bgs->ckpt_started;
bgs->ckpt_flags |= flags;
SpinLockRelease(&bgs->ckpt_lck);
/*
* Send signal to request checkpoint. It's possible that the checkpointer
* hasn't started yet, or is in process of restarting, so we will retry a
* few times if needed. Also, if not told to wait for the checkpoint to
* occur, we consider failure to send the signal to be nonfatal and merely
* LOG it.
*/
for (ntries = 0;; ntries++)
{
if (BgWriterShmem->checkpointer_pid == 0)
{
if (ntries >= 20) /* max wait 2.0 sec */
{
elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
"could not request checkpoint because checkpointer not running");
break;
}
}
else if (kill(BgWriterShmem->checkpointer_pid, SIGINT) != 0)
{
if (ntries >= 20) /* max wait 2.0 sec */
{
elog((flags & CHECKPOINT_WAIT) ? ERROR : LOG,
"could not signal for checkpoint: %m");
break;
}
}
else
break; /* signal sent successfully */
CHECK_FOR_INTERRUPTS();
pg_usleep(100000L); /* wait 0.1 sec, then retry */
}
/*
* If requested, wait for completion. We detect completion according to
* the algorithm given above.
*/
if (flags & CHECKPOINT_WAIT)
{
int new_started,
new_failed;
/* Wait for a new checkpoint to start. */
for (;;)
{
SpinLockAcquire(&bgs->ckpt_lck);
new_started = bgs->ckpt_started;
SpinLockRelease(&bgs->ckpt_lck);
if (new_started != old_started)
break;
CHECK_FOR_INTERRUPTS();
pg_usleep(100000L);
}
/*
* We are waiting for ckpt_done >= new_started, in a modulo sense.
*/
for (;;)
{
int new_done;
SpinLockAcquire(&bgs->ckpt_lck);
new_done = bgs->ckpt_done;
new_failed = bgs->ckpt_failed;
SpinLockRelease(&bgs->ckpt_lck);
if (new_done - new_started >= 0)
break;
CHECK_FOR_INTERRUPTS();
pg_usleep(100000L);
}
if (new_failed != old_failed)
ereport(ERROR,
(errmsg("checkpoint request failed"),
errhint("Consult recent messages in the server log for details.")));
}
}
/*
* ForwardFsyncRequest
* Forward a file-fsync request from a backend to the checkpointer
*
* Whenever a backend is compelled to write directly to a relation
* (which should be seldom, if the checkpointer is getting its job done),
* the backend calls this routine to pass over knowledge that the relation
* is dirty and must be fsync'd before next checkpoint. We also use this
* opportunity to count such writes for statistical purposes.
*
* segno specifies which segment (not block!) of the relation needs to be
* fsync'd. (Since the valid range is much less than BlockNumber, we can
* use high values for special flags; that's all internal to md.c, which
* see for details.)
*
* To avoid holding the lock for longer than necessary, we normally write
* to the requests[] queue without checking for duplicates. The checkpointer
* will have to eliminate dups internally anyway. However, if we discover
* that the queue is full, we make a pass over the entire queue to compact
* it. This is somewhat expensive, but the alternative is for the backend
* to perform its own fsync, which is far more expensive in practice. It
* is theoretically possible a backend fsync might still be necessary, if
* the queue is full and contains no duplicate entries. In that case, we
* let the backend know by returning false.
*/
bool
ForwardFsyncRequest(RelFileNodeBackend rnode, ForkNumber forknum,
BlockNumber segno)
{
BgWriterRequest *request;
if (!IsUnderPostmaster)
return false; /* probably shouldn't even get here */
if (am_checkpointer)
elog(ERROR, "ForwardFsyncRequest must not be called in checkpointer");
LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE);
/* Count all backend writes regardless of if they fit in the queue */
BgWriterShmem->num_backend_writes++;
/*
* If the background writer isn't running or the request queue is full,
* the backend will have to perform its own fsync request. But before
* forcing that to happen, we can try to compact the background writer
* request queue.
*/
if (BgWriterShmem->checkpointer_pid == 0 ||
(BgWriterShmem->num_requests >= BgWriterShmem->max_requests
&& !CompactCheckpointerRequestQueue()))
{
/*
* Count the subset of writes where backends have to do their own
* fsync
*/
BgWriterShmem->num_backend_fsync++;
LWLockRelease(BgWriterCommLock);
return false;
}
request = &BgWriterShmem->requests[BgWriterShmem->num_requests++];
request->rnode = rnode;
request->forknum = forknum;
request->segno = segno;
LWLockRelease(BgWriterCommLock);
return true;
}
/*
* CompactCheckpointerRequestQueue
* Remove duplicates from the request queue to avoid backend fsyncs.
*
* Although a full fsync request queue is not common, it can lead to severe
* performance problems when it does happen. So far, this situation has
* only been observed to occur when the system is under heavy write load,
* and especially during the "sync" phase of a checkpoint. Without this
* logic, each backend begins doing an fsync for every block written, which
* gets very expensive and can slow down the whole system.
*
* Trying to do this every time the queue is full could lose if there
* aren't any removable entries. But should be vanishingly rare in
* practice: there's one queue entry per shared buffer.
*/
static bool
CompactCheckpointerRequestQueue()
{
struct BgWriterSlotMapping
{
BgWriterRequest request;
int slot;
};
int n,
preserve_count;
int num_skipped = 0;
HASHCTL ctl;
HTAB *htab;
bool *skip_slot;
/* must hold BgWriterCommLock in exclusive mode */
Assert(LWLockHeldByMe(BgWriterCommLock));
/* Initialize temporary hash table */
MemSet(&ctl, 0, sizeof(ctl));
ctl.keysize = sizeof(BgWriterRequest);
ctl.entrysize = sizeof(struct BgWriterSlotMapping);
ctl.hash = tag_hash;
htab = hash_create("CompactCheckpointerRequestQueue",
BgWriterShmem->num_requests,
&ctl,
HASH_ELEM | HASH_FUNCTION);
/* Initialize skip_slot array */
skip_slot = palloc0(sizeof(bool) * BgWriterShmem->num_requests);
/*
* The basic idea here is that a request can be skipped if it's followed
* by a later, identical request. It might seem more sensible to work
* backwards from the end of the queue and check whether a request is
* *preceded* by an earlier, identical request, in the hopes of doing less
* copying. But that might change the semantics, if there's an
* intervening FORGET_RELATION_FSYNC or FORGET_DATABASE_FSYNC request, so
* we do it this way. It would be possible to be even smarter if we made
* the code below understand the specific semantics of such requests (it
* could blow away preceding entries that would end up being canceled
* anyhow), but it's not clear that the extra complexity would buy us
* anything.
*/
for (n = 0; n < BgWriterShmem->num_requests; ++n)
{
BgWriterRequest *request;
struct BgWriterSlotMapping *slotmap;
bool found;
request = &BgWriterShmem->requests[n];
slotmap = hash_search(htab, request, HASH_ENTER, &found);
if (found)
{
skip_slot[slotmap->slot] = true;
++num_skipped;
}
slotmap->slot = n;
}
/* Done with the hash table. */
hash_destroy(htab);
/* If no duplicates, we're out of luck. */
if (!num_skipped)
{
pfree(skip_slot);
return false;
}
/* We found some duplicates; remove them. */
for (n = 0, preserve_count = 0; n < BgWriterShmem->num_requests; ++n)
{
if (skip_slot[n])
continue;
BgWriterShmem->requests[preserve_count++] = BgWriterShmem->requests[n];
}
ereport(DEBUG1,
(errmsg("compacted fsync request queue from %d entries to %d entries",
BgWriterShmem->num_requests, preserve_count)));
BgWriterShmem->num_requests = preserve_count;
/* Cleanup. */
pfree(skip_slot);
return true;
}
/*
* AbsorbFsyncRequests
* Retrieve queued fsync requests and pass them to local smgr.
*
* This is exported because it must be called during CreateCheckPoint;
* we have to be sure we have accepted all pending requests just before
* we start fsync'ing. Since CreateCheckPoint sometimes runs in
* non-checkpointer processes, do nothing if not checkpointer.
*/
void
AbsorbFsyncRequests(void)
{
BgWriterRequest *requests = NULL;
BgWriterRequest *request;
int n;
if (!am_checkpointer)
return;
/*
* We have to PANIC if we fail to absorb all the pending requests (eg,
* because our hashtable runs out of memory). This is because the system
* cannot run safely if we are unable to fsync what we have been told to
* fsync. Fortunately, the hashtable is so small that the problem is
* quite unlikely to arise in practice.
*/
START_CRIT_SECTION();
/*
* We try to avoid holding the lock for a long time by copying the request
* array.
*/
LWLockAcquire(BgWriterCommLock, LW_EXCLUSIVE);
/* Transfer write count into pending pgstats message */
BgWriterStats.m_buf_written_backend += BgWriterShmem->num_backend_writes;
BgWriterStats.m_buf_fsync_backend += BgWriterShmem->num_backend_fsync;
BgWriterShmem->num_backend_writes = 0;
BgWriterShmem->num_backend_fsync = 0;
n = BgWriterShmem->num_requests;
if (n > 0)
{
requests = (BgWriterRequest *) palloc(n * sizeof(BgWriterRequest));
memcpy(requests, BgWriterShmem->requests, n * sizeof(BgWriterRequest));
}
BgWriterShmem->num_requests = 0;
LWLockRelease(BgWriterCommLock);
for (request = requests; n > 0; request++, n--)
RememberFsyncRequest(request->rnode, request->forknum, request->segno);
if (requests)
pfree(requests);
END_CRIT_SECTION();
}
/*
* Update any shared memory configurations based on config parameters
*/
static void
UpdateSharedMemoryConfig(void)
{
/* update global shmem state for sync rep */
SyncRepUpdateSyncStandbysDefined();
/*
* If full_page_writes has been changed by SIGHUP, we update it
* in shared memory and write an XLOG_FPW_CHANGE record.
*/
UpdateFullPageWrites();
elog(DEBUG2, "checkpointer updated shared memory configuration values");
}
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