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/*
* contrib/pg_standby/pg_standby.c
*
*
* pg_standby.c
*
* Production-ready example of how to create a Warm Standby
* database server using continuous archiving as a
* replication mechanism
*
* We separate the parameters for archive and nextWALfile
* so that we can check the archive exists, even if the
* WAL file doesn't (yet).
*
* This program will be executed once in full for each file
* requested by the warm standby server.
*
* It is designed to cater to a variety of needs, as well
* providing a customizable section.
*
* Original author: Simon Riggs simon@2ndquadrant.com
* Current maintainer: Simon Riggs
*/
#include "postgres_fe.h"
#include <ctype.h>
#include <dirent.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/time.h>
#include "pg_getopt.h"
#include "access/xlog_internal.h"
const char *progname;
/* Options and defaults */
int sleeptime = 5; /* amount of time to sleep between file checks */
int waittime = -1; /* how long we have been waiting, -1 no wait
* yet */
int maxwaittime = 0; /* how long are we prepared to wait for? */
int keepfiles = 0; /* number of WAL files to keep, 0 keep all */
int maxretries = 3; /* number of retries on restore command */
bool debug = false; /* are we debugging? */
bool need_cleanup = false; /* do we need to remove files from
* archive? */
#ifndef WIN32
static volatile sig_atomic_t signaled = false;
#endif
char *archiveLocation; /* where to find the archive? */
char *triggerPath; /* where to find the trigger file? */
char *xlogFilePath; /* where we are going to restore to */
char *nextWALFileName; /* the file we need to get from archive */
char *restartWALFileName; /* the file from which we can restart restore */
char *priorWALFileName; /* the file we need to get from archive */
char WALFilePath[MAXPGPATH]; /* the file path including archive */
char restoreCommand[MAXPGPATH]; /* run this to restore */
char exclusiveCleanupFileName[MAXFNAMELEN]; /* the file we need to
* get from archive */
/*
* Two types of failover are supported (smart and fast failover).
*
* The content of the trigger file determines the type of failover. If the
* trigger file contains the word "smart" (or the file is empty), smart
* failover is chosen: pg_standby acts as cp or ln command itself, on
* successful completion all the available WAL records will be applied
* resulting in zero data loss. But, it might take a long time to finish
* recovery if there's a lot of unapplied WAL.
*
* On the other hand, if the trigger file contains the word "fast", the
* recovery is finished immediately even if unapplied WAL files remain. Any
* transactions in the unapplied WAL files are lost.
*
* An empty trigger file performs smart failover. SIGUSR or SIGINT triggers
* fast failover. A timeout causes fast failover (smart failover would have
* the same effect, since if the timeout is reached there is no unapplied WAL).
*/
#define NoFailover 0
#define SmartFailover 1
#define FastFailover 2
static int Failover = NoFailover;
#define RESTORE_COMMAND_COPY 0
#define RESTORE_COMMAND_LINK 1
int restoreCommandType;
#define XLOG_DATA 0
#define XLOG_HISTORY 1
#define XLOG_BACKUP_LABEL 2
int nextWALFileType;
#define SET_RESTORE_COMMAND(cmd, arg1, arg2) \
snprintf(restoreCommand, MAXPGPATH, cmd " \"%s\" \"%s\"", arg1, arg2)
struct stat stat_buf;
/* =====================================================================
*
* Customizable section
*
* =====================================================================
*
* Currently, this section assumes that the Archive is a locally
* accessible directory. If you want to make other assumptions,
* such as using a vendor-specific archive and access API, these
* routines are the ones you'll need to change. You're
* encouraged to submit any changes to pgsql-hackers@postgresql.org
* or personally to the current maintainer. Those changes may be
* folded in to later versions of this program.
*/
/*
* Initialize allows customized commands into the warm standby program.
*
* As an example, and probably the common case, we use either
* cp/ln commands on *nix, or copy/move command on Windows.
*/
static void
CustomizableInitialize(void)
{
#ifdef WIN32
snprintf(WALFilePath, MAXPGPATH, "%s\\%s", archiveLocation, nextWALFileName);
switch (restoreCommandType)
{
case RESTORE_COMMAND_LINK:
SET_RESTORE_COMMAND("mklink", WALFilePath, xlogFilePath);
break;
case RESTORE_COMMAND_COPY:
default:
SET_RESTORE_COMMAND("copy", WALFilePath, xlogFilePath);
break;
}
#else
snprintf(WALFilePath, MAXPGPATH, "%s/%s", archiveLocation, nextWALFileName);
switch (restoreCommandType)
{
case RESTORE_COMMAND_LINK:
#if HAVE_WORKING_LINK
SET_RESTORE_COMMAND("ln -s -f", WALFilePath, xlogFilePath);
break;
#endif
case RESTORE_COMMAND_COPY:
default:
SET_RESTORE_COMMAND("cp", WALFilePath, xlogFilePath);
break;
}
#endif
/*
* This code assumes that archiveLocation is a directory You may wish to
* add code to check for tape libraries, etc.. So, since it is a
* directory, we use stat to test if it's accessible
*/
if (stat(archiveLocation, &stat_buf) != 0)
{
fprintf(stderr, "%s: archive location \"%s\" does not exist\n", progname, archiveLocation);
fflush(stderr);
exit(2);
}
}
/*
* CustomizableNextWALFileReady()
*
* Is the requested file ready yet?
*/
static bool
CustomizableNextWALFileReady(void)
{
if (stat(WALFilePath, &stat_buf) == 0)
{
/*
* If it's a backup file, return immediately. If it's a regular file
* return only if it's the right size already.
*/
if (IsBackupHistoryFileName(nextWALFileName))
{
nextWALFileType = XLOG_BACKUP_LABEL;
return true;
}
else if (stat_buf.st_size == XLOG_SEG_SIZE)
{
#ifdef WIN32
/*
* Windows 'cp' sets the final file size before the copy is
* complete, and not yet ready to be opened by pg_standby. So we
* wait for sleeptime secs before attempting to restore. If that
* is not enough, we will rely on the retry/holdoff mechanism.
* GNUWin32's cp does not have this problem.
*/
pg_usleep(sleeptime * 1000000L);
#endif
nextWALFileType = XLOG_DATA;
return true;
}
/*
* If still too small, wait until it is the correct size
*/
if (stat_buf.st_size > XLOG_SEG_SIZE)
{
if (debug)
{
fprintf(stderr, "file size greater than expected\n");
fflush(stderr);
}
exit(3);
}
}
return false;
}
#define MaxSegmentsPerLogFile ( 0xFFFFFFFF / XLOG_SEG_SIZE )
static void
CustomizableCleanupPriorWALFiles(void)
{
/*
* Work out name of prior file from current filename
*/
if (nextWALFileType == XLOG_DATA)
{
int rc;
DIR *xldir;
struct dirent *xlde;
/*
* Assume it's OK to keep failing. The failure situation may change
* over time, so we'd rather keep going on the main processing than
* fail because we couldn't clean up yet.
*/
if ((xldir = opendir(archiveLocation)) != NULL)
{
while (errno = 0, (xlde = readdir(xldir)) != NULL)
{
/*
* We ignore the timeline part of the XLOG segment identifiers
* in deciding whether a segment is still needed. This
* ensures that we won't prematurely remove a segment from a
* parent timeline. We could probably be a little more
* proactive about removing segments of non-parent timelines,
* but that would be a whole lot more complicated.
*
* We use the alphanumeric sorting property of the filenames
* to decide which ones are earlier than the
* exclusiveCleanupFileName file. Note that this means files
* are not removed in the order they were originally written,
* in case this worries you.
*/
if (IsXLogFileName(xlde->d_name) &&
strcmp(xlde->d_name + 8, exclusiveCleanupFileName + 8) < 0)
{
#ifdef WIN32
snprintf(WALFilePath, MAXPGPATH, "%s\\%s", archiveLocation, xlde->d_name);
#else
snprintf(WALFilePath, MAXPGPATH, "%s/%s", archiveLocation, xlde->d_name);
#endif
if (debug)
fprintf(stderr, "\nremoving file \"%s\"", WALFilePath);
rc = unlink(WALFilePath);
if (rc != 0)
{
fprintf(stderr, "\n%s: ERROR: could not remove file \"%s\": %s\n",
progname, WALFilePath, strerror(errno));
break;
}
}
}
if (errno)
fprintf(stderr, "%s: could not read archive location \"%s\": %s\n",
progname, archiveLocation, strerror(errno));
if (debug)
fprintf(stderr, "\n");
}
else
fprintf(stderr, "%s: could not open archive location \"%s\": %s\n",
progname, archiveLocation, strerror(errno));
if (closedir(xldir))
fprintf(stderr, "%s: could not close archive location \"%s\": %s\n",
progname, archiveLocation, strerror(errno));
fflush(stderr);
}
}
/* =====================================================================
* End of Customizable section
* =====================================================================
*/
/*
* SetWALFileNameForCleanup()
*
* Set the earliest WAL filename that we want to keep on the archive
* and decide whether we need_cleanup
*/
static bool
SetWALFileNameForCleanup(void)
{
uint32 tli = 1,
log = 0,
seg = 0;
uint32 log_diff = 0,
seg_diff = 0;
bool cleanup = false;
if (restartWALFileName)
{
/*
* Don't do cleanup if the restartWALFileName provided is later than
* the xlog file requested. This is an error and we must not remove
* these files from archive. This shouldn't happen, but better safe
* than sorry.
*/
if (strcmp(restartWALFileName, nextWALFileName) > 0)
return false;
strlcpy(exclusiveCleanupFileName, restartWALFileName, sizeof(exclusiveCleanupFileName));
return true;
}
if (keepfiles > 0)
{
sscanf(nextWALFileName, "%08X%08X%08X", &tli, &log, &seg);
if (tli > 0 && seg > 0)
{
log_diff = keepfiles / MaxSegmentsPerLogFile;
seg_diff = keepfiles % MaxSegmentsPerLogFile;
if (seg_diff > seg)
{
log_diff++;
seg = MaxSegmentsPerLogFile - (seg_diff - seg);
}
else
seg -= seg_diff;
if (log >= log_diff)
{
log -= log_diff;
cleanup = true;
}
else
{
log = 0;
seg = 0;
}
}
}
XLogFileNameById(exclusiveCleanupFileName, tli, log, seg);
return cleanup;
}
/*
* CheckForExternalTrigger()
*
* Is there a trigger file? Sets global 'Failover' variable to indicate
* what kind of a trigger file it was. A "fast" trigger file is turned
* into a "smart" file as a side-effect.
*/
static void
CheckForExternalTrigger(void)
{
char buf[32];
int fd;
int len;
/*
* Look for a trigger file, if that option has been selected
*
* We use stat() here because triggerPath is always a file rather than
* potentially being in an archive
*/
if (!triggerPath || stat(triggerPath, &stat_buf) != 0)
return;
/*
* An empty trigger file performs smart failover. There's a little race
* condition here: if the writer of the trigger file has just created the
* file, but not yet written anything to it, we'll treat that as smart
* shutdown even if the other process was just about to write "fast" to
* it. But that's fine: we'll restore one more WAL file, and when we're
* invoked next time, we'll see the word "fast" and fail over immediately.
*/
if (stat_buf.st_size == 0)
{
Failover = SmartFailover;
fprintf(stderr, "trigger file found: smart failover\n");
fflush(stderr);
return;
}
if ((fd = open(triggerPath, O_RDWR, 0)) < 0)
{
fprintf(stderr, "WARNING: could not open \"%s\": %s\n",
triggerPath, strerror(errno));
fflush(stderr);
return;
}
if ((len = read(fd, buf, sizeof(buf) - 1)) < 0)
{
fprintf(stderr, "WARNING: could not read \"%s\": %s\n",
triggerPath, strerror(errno));
fflush(stderr);
close(fd);
return;
}
buf[len] = '\0';
if (strncmp(buf, "smart", 5) == 0)
{
Failover = SmartFailover;
fprintf(stderr, "trigger file found: smart failover\n");
fflush(stderr);
close(fd);
return;
}
if (strncmp(buf, "fast", 4) == 0)
{
Failover = FastFailover;
fprintf(stderr, "trigger file found: fast failover\n");
fflush(stderr);
/*
* Turn it into a "smart" trigger by truncating the file. Otherwise if
* the server asks us again to restore a segment that was restored
* already, we would return "not found" and upset the server.
*/
if (ftruncate(fd, 0) < 0)
{
fprintf(stderr, "WARNING: could not read \"%s\": %s\n",
triggerPath, strerror(errno));
fflush(stderr);
}
close(fd);
return;
}
close(fd);
fprintf(stderr, "WARNING: invalid content in \"%s\"\n", triggerPath);
fflush(stderr);
return;
}
/*
* RestoreWALFileForRecovery()
*
* Perform the action required to restore the file from archive
*/
static bool
RestoreWALFileForRecovery(void)
{
int rc = 0;
int numretries = 0;
if (debug)
{
fprintf(stderr, "running restore: ");
fflush(stderr);
}
while (numretries <= maxretries)
{
rc = system(restoreCommand);
if (rc == 0)
{
if (debug)
{
fprintf(stderr, "OK\n");
fflush(stderr);
}
return true;
}
pg_usleep(numretries++ * sleeptime * 1000000L);
}
/*
* Allow caller to add additional info
*/
if (debug)
fprintf(stderr, "not restored\n");
return false;
}
static void
usage(void)
{
printf("%s allows PostgreSQL warm standby servers to be configured.\n\n", progname);
printf("Usage:\n");
printf(" %s [OPTION]... ARCHIVELOCATION NEXTWALFILE XLOGFILEPATH [RESTARTWALFILE]\n", progname);
printf("\nOptions:\n");
printf(" -c copy file from archive (default)\n");
printf(" -d generate lots of debugging output (testing only)\n");
printf(" -k NUMFILESTOKEEP if RESTARTWALFILE is not used, remove files prior to limit\n"
" (0 keeps all)\n");
printf(" -l does nothing; use of link is now deprecated\n");
printf(" -r MAXRETRIES max number of times to retry, with progressive wait\n"
" (default=3)\n");
printf(" -s SLEEPTIME seconds to wait between file checks (min=1, max=60,\n"
" default=5)\n");
printf(" -t TRIGGERFILE trigger file to initiate failover (no default)\n");
printf(" -V, --version output version information, then exit\n");
printf(" -w MAXWAITTIME max seconds to wait for a file (0=no limit) (default=0)\n");
printf(" -?, --help show this help, then exit\n");
printf("\n"
"Main intended use as restore_command in recovery.conf:\n"
" restore_command = 'pg_standby [OPTION]... ARCHIVELOCATION %%f %%p %%r'\n"
"e.g.\n"
" restore_command = 'pg_standby /mnt/server/archiverdir %%f %%p %%r'\n");
printf("\nReport bugs to <pgsql-bugs@postgresql.org>.\n");
}
#ifndef WIN32
static void
sighandler(int sig)
{
signaled = true;
}
/* We don't want SIGQUIT to core dump */
static void
sigquit_handler(int sig)
{
pqsignal(SIGINT, SIG_DFL);
kill(getpid(), SIGINT);
}
#endif
/*------------ MAIN ----------------------------------------*/
int
main(int argc, char **argv)
{
int c;
progname = get_progname(argv[0]);
if (argc > 1)
{
if (strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-?") == 0)
{
usage();
exit(0);
}
if (strcmp(argv[1], "--version") == 0 || strcmp(argv[1], "-V") == 0)
{
puts("pg_standby (PostgreSQL) " PG_VERSION);
exit(0);
}
}
#ifndef WIN32
/*
* You can send SIGUSR1 to trigger failover.
*
* Postmaster uses SIGQUIT to request immediate shutdown. The default
* action is to core dump, but we don't want that, so trap it and commit
* suicide without core dump.
*
* We used to use SIGINT and SIGQUIT to trigger failover, but that turned
* out to be a bad idea because postmaster uses SIGQUIT to request
* immediate shutdown. We still trap SIGINT, but that may change in a
* future release.
*
* There's no way to trigger failover via signal on Windows.
*/
(void) pqsignal(SIGUSR1, sighandler);
(void) pqsignal(SIGINT, sighandler); /* deprecated, use SIGUSR1 */
(void) pqsignal(SIGQUIT, sigquit_handler);
#endif
while ((c = getopt(argc, argv, "cdk:lr:s:t:w:")) != -1)
{
switch (c)
{
case 'c': /* Use copy */
restoreCommandType = RESTORE_COMMAND_COPY;
break;
case 'd': /* Debug mode */
debug = true;
break;
case 'k': /* keepfiles */
keepfiles = atoi(optarg);
if (keepfiles < 0)
{
fprintf(stderr, "%s: -k keepfiles must be >= 0\n", progname);
exit(2);
}
break;
case 'l': /* Use link */
/*
* Link feature disabled, possibly permanently. Linking causes
* a problem after recovery ends that is not currently
* resolved by PostgreSQL. 25 Jun 2009
*/
#ifdef NOT_USED
restoreCommandType = RESTORE_COMMAND_LINK;
#endif
break;
case 'r': /* Retries */
maxretries = atoi(optarg);
if (maxretries < 0)
{
fprintf(stderr, "%s: -r maxretries must be >= 0\n", progname);
exit(2);
}
break;
case 's': /* Sleep time */
sleeptime = atoi(optarg);
if (sleeptime <= 0 || sleeptime > 60)
{
fprintf(stderr, "%s: -s sleeptime incorrectly set\n", progname);
exit(2);
}
break;
case 't': /* Trigger file */
triggerPath = pg_strdup(optarg);
break;
case 'w': /* Max wait time */
maxwaittime = atoi(optarg);
if (maxwaittime < 0)
{
fprintf(stderr, "%s: -w maxwaittime incorrectly set\n", progname);
exit(2);
}
break;
default:
fprintf(stderr, "Try \"%s --help\" for more information.\n", progname);
exit(2);
break;
}
}
/*
* Parameter checking - after checking to see if trigger file present
*/
if (argc == 1)
{
fprintf(stderr, "%s: not enough command-line arguments\n", progname);
exit(2);
}
/*
* We will go to the archiveLocation to get nextWALFileName.
* nextWALFileName may not exist yet, which would not be an error, so we
* separate the archiveLocation and nextWALFileName so we can check
* separately whether archiveLocation exists, if not that is an error
*/
if (optind < argc)
{
archiveLocation = argv[optind];
optind++;
}
else
{
fprintf(stderr, "%s: must specify archive location\n", progname);
fprintf(stderr, "Try \"%s --help\" for more information.\n", progname);
exit(2);
}
if (optind < argc)
{
nextWALFileName = argv[optind];
optind++;
}
else
{
fprintf(stderr, "%s: must specify WAL file name as second non-option argument (use \"%%f\")\n", progname);
fprintf(stderr, "Try \"%s --help\" for more information.\n", progname);
exit(2);
}
if (optind < argc)
{
xlogFilePath = argv[optind];
optind++;
}
else
{
fprintf(stderr, "%s: must specify xlog destination as third non-option argument (use \"%%p\")\n", progname);
fprintf(stderr, "Try \"%s --help\" for more information.\n", progname);
exit(2);
}
if (optind < argc)
{
restartWALFileName = argv[optind];
optind++;
}
CustomizableInitialize();
need_cleanup = SetWALFileNameForCleanup();
if (debug)
{
fprintf(stderr, "Trigger file: %s\n", triggerPath ? triggerPath : "<not set>");
fprintf(stderr, "Waiting for WAL file: %s\n", nextWALFileName);
fprintf(stderr, "WAL file path: %s\n", WALFilePath);
fprintf(stderr, "Restoring to: %s\n", xlogFilePath);
fprintf(stderr, "Sleep interval: %d second%s\n",
sleeptime, (sleeptime > 1 ? "s" : " "));
fprintf(stderr, "Max wait interval: %d %s\n",
maxwaittime, (maxwaittime > 0 ? "seconds" : "forever"));
fprintf(stderr, "Command for restore: %s\n", restoreCommand);
fprintf(stderr, "Keep archive history: ");
if (need_cleanup)
fprintf(stderr, "%s and later\n", exclusiveCleanupFileName);
else
fprintf(stderr, "no cleanup required\n");
fflush(stderr);
}
/*
* Check for initial history file: always the first file to be requested
* It's OK if the file isn't there - all other files need to wait
*/
if (IsTLHistoryFileName(nextWALFileName))
{
nextWALFileType = XLOG_HISTORY;
if (RestoreWALFileForRecovery())
exit(0);
else
{
if (debug)
{
fprintf(stderr, "history file not found\n");
fflush(stderr);
}
exit(1);
}
}
/*
* Main wait loop
*/
for (;;)
{
/* Check for trigger file or signal first */
CheckForExternalTrigger();
#ifndef WIN32
if (signaled)
{
Failover = FastFailover;
if (debug)
{
fprintf(stderr, "signaled to exit: fast failover\n");
fflush(stderr);
}
}
#endif
/*
* Check for fast failover immediately, before checking if the
* requested WAL file is available
*/
if (Failover == FastFailover)
exit(1);
if (CustomizableNextWALFileReady())
{
/*
* Once we have restored this file successfully we can remove some
* prior WAL files. If this restore fails we musn't remove any
* file because some of them will be requested again immediately
* after the failed restore, or when we restart recovery.
*/
if (RestoreWALFileForRecovery())
{
if (need_cleanup)
CustomizableCleanupPriorWALFiles();
exit(0);
}
else
{
/* Something went wrong in copying the file */
exit(1);
}
}
/* Check for smart failover if the next WAL file was not available */
if (Failover == SmartFailover)
exit(1);
if (sleeptime <= 60)
pg_usleep(sleeptime * 1000000L);
waittime += sleeptime;
if (waittime >= maxwaittime && maxwaittime > 0)
{
Failover = FastFailover;
if (debug)
{
fprintf(stderr, "Timed out after %d seconds: fast failover\n",
waittime);
fflush(stderr);
}
}
if (debug)
{
fprintf(stderr, "WAL file not present yet.");
if (triggerPath)
fprintf(stderr, " Checking for trigger file...");
fprintf(stderr, "\n");
fflush(stderr);
}
}
}