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Commit5adafaf

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Have pg_rewind run crash recovery before rewinding
If we don't do this, the rewind fails if the server wasn't cleanly shutdown, which seems unhelpful serving no purpose.Also provide a new option --no-ensure-shutdown to suppress thisbehavior, for alleged advanced usage that prefers to avoid the crashrecovery.Authors: Paul Guo, Jimmy Yih, Ashwin AgrawalReviewed-by: Álvaro HerreraDiscussion:https://postgr.es/m/CAEET0ZEffUkXc48pg2iqARQgGRYDiiVxDu+yYek_bTwJF+q=Uw@mail.gmail.com
1 parentc967e13 commit5adafaf

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2 files changed

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‎doc/src/sgml/ref/pg_rewind.sgml‎

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Original file line numberDiff line numberDiff line change
@@ -165,6 +165,21 @@ PostgreSQL documentation
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--no-ensure-shutdown</option></term>
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<listitem>
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<para>
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<application>pg_rewind</application> verifies that the target server
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is cleanly shutdown before rewinding; by default, if it isn't, it
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starts the server in single-user mode to complete crash recovery.
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By passing this option, <application>pg_rewind</application> skips
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this and errors out immediately if the server is not cleanly shut
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down. Users are expected to handle the situation themselves in that
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case.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>-n</option></term>
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<term><option>--dry-run</option></term>

‎src/bin/pg_rewind/pg_rewind.c‎

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Original file line numberDiff line numberDiff line change
@@ -40,6 +40,7 @@ static void digestControlFile(ControlFileData *ControlFile, char *source,
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staticvoidsyncTargetDirectory(void);
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staticvoidsanityChecks(void);
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staticvoidfindCommonAncestorTimeline(XLogRecPtr*recptr,int*tliIndex);
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staticvoidensureCleanShutdown(constchar*argv0);
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staticControlFileDataControlFile_target;
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staticControlFileDataControlFile_source;
@@ -79,6 +80,7 @@ usage(const char *progname)
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printf(_(" -N, --no-sync do not wait for changes to be written\n"
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" safely to disk\n"));
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printf(_(" -P, --progress write progress messages\n"));
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printf(_(" --no-ensure-shutdown do not automatically fix unclean shutdown\n"));
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printf(_(" --debug write a lot of debug messages\n"));
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printf(_(" -V, --version output version information, then exit\n"));
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printf(_(" -?, --help show this help, then exit\n"));
@@ -94,6 +96,7 @@ main(int argc, char **argv)
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{"target-pgdata",required_argument,NULL,'D'},
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{"source-pgdata",required_argument,NULL,1},
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{"source-server",required_argument,NULL,2},
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{"no-ensure-shutdown",no_argument,NULL,44},
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{"version",no_argument,NULL,'V'},
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{"dry-run",no_argument,NULL,'n'},
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{"no-sync",no_argument,NULL,'N'},
@@ -110,6 +113,7 @@ main(int argc, char **argv)
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XLogRecPtrchkptredo;
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size_tsize;
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char*buffer;
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boolno_ensure_shutdown= false;
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boolrewind_needed;
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XLogRecPtrendrec;
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TimeLineIDendtli;
@@ -169,6 +173,9 @@ main(int argc, char **argv)
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case2:/* --source-server */
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connstr_source=pg_strdup(optarg);
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break;
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case4:
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no_ensure_shutdown= true;
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break;
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}
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}
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@@ -241,6 +248,24 @@ main(int argc, char **argv)
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digestControlFile(&ControlFile_target,buffer,size);
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pg_free(buffer);
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/*
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* If the target instance was not cleanly shut down, run a single-user
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* postgres session really quickly and reload the control file to get the
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* new state. Note if no_ensure_shutdown is specified, pg_rewind won't do
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* that automatically. That means users need to do themselves in advance,
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* else pg_rewind will soon quit, see sanityChecks().
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*/
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if (!no_ensure_shutdown&&
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ControlFile_target.state!=DB_SHUTDOWNED&&
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ControlFile_target.state!=DB_SHUTDOWNED_IN_RECOVERY)
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{
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ensureCleanShutdown(argv[0]);
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buffer=slurpFile(datadir_target,"global/pg_control",&size);
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digestControlFile(&ControlFile_target,buffer,size);
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pg_free(buffer);
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}
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buffer=fetchFile("global/pg_control",&size);
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digestControlFile(&ControlFile_source,buffer,size);
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pg_free(buffer);
@@ -748,3 +773,58 @@ syncTargetDirectory(void)
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fsync_pgdata(datadir_target,PG_VERSION_NUM);
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}
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/*
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* Ensure clean shutdown of target instance by launching single-user mode
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* postgres to do crash recovery.
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*/
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staticvoid
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ensureCleanShutdown(constchar*argv0)
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{
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intret;
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#defineMAXCMDLEN (2 * MAXPGPATH)
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charexec_path[MAXPGPATH];
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charcmd[MAXCMDLEN];
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/* locate postgres binary */
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if ((ret=find_other_exec(argv0,"postgres",
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PG_BACKEND_VERSIONSTR,
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exec_path))<0)
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{
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charfull_path[MAXPGPATH];
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if (find_my_exec(argv0,full_path)<0)
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strlcpy(full_path,progname,sizeof(full_path));
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if (ret==-1)
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pg_fatal("The program \"%s\" is needed by %s but was\n"
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"not found in the same directory as \"%s\".\n"
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"Check your installation.",
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"postgres",progname,full_path);
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else
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pg_fatal("The program \"%s\" was found by \"%s\" but was\n"
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"not the same version as %s.\n"
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"Check your installation.",
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"postgres",full_path,progname);
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}
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pg_log_info("executing \"%s\" for target server to complete crash recovery",
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exec_path);
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/*
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* Skip processing if requested, but only after ensuring presence of
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* postgres.
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*/
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if (dry_run)
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return;
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/* finally run postgres in single-user mode */
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snprintf(cmd,MAXCMDLEN,"\"%s\" --single -D \"%s\" template1 < \"%s\"",
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exec_path,datadir_target,DEVNULL);
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if (system(cmd)!=0)
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{
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pg_log_error("postgres single-user mode of target instance failed");
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pg_fatal("Command was: %s",cmd);
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}
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}

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