From 309649dfa2eea9d696e43271057da7e643d771b4 Mon Sep 17 00:00:00 2001 From: Jeremie Grauer Date: Mon, 7 Nov 2022 23:50:43 +0100 Subject: [PATCH] adds the option --no-ensure-full-page-writes to pg_rewind --- doc/src/sgml/ref/pg_rewind.sgml | 27 +++++++++++++++++++- src/bin/pg_rewind/libpq_source.c | 22 ++++++++++------ src/bin/pg_rewind/pg_rewind.c | 43 +++++++++++++++++++------------- src/bin/pg_rewind/pg_rewind.h | 1 + 4 files changed, 67 insertions(+), 26 deletions(-) diff --git a/doc/src/sgml/ref/pg_rewind.sgml b/doc/src/sgml/ref/pg_rewind.sgml index 69d6924b3a..64ee600c2b 100644 --- a/doc/src/sgml/ref/pg_rewind.sgml +++ b/doc/src/sgml/ref/pg_rewind.sgml @@ -99,7 +99,13 @@ PostgreSQL documentation in postgresql.conf or data checksums enabled when the cluster was initialized with initdb. Neither of these are currently on by default. - must also be set to on, but is enabled by default. + should also be set to on (which is the default) when the + underlying file system can write data in an increment of less than the page size. + Some file systems (like ZFS when configured with a recordsize as a multiple of + the page size) don't need this parameter since they will never write less than a + complete page to disk. If you are running such a system, you can add the option + --no-enforce-full-page-writes so that pg_rewind will run + even when is set to off. @@ -283,6 +289,25 @@ PostgreSQL documentation + + + + + pg_rewind by default requires that + is set to on. This ensures that pg_rewind do + not run into torn pages while running. This option is necessary most of + the time since very few filesystems enforce the flush of full page to disk. + One such system is ZFS where the page is always flushed to disk in its + entirety. Other storage system may also have the same warranty. This option + is here to allow pg_rewind to run on such systems without enforcing that + is on. It's important to know what + you are doing before setting this setting because in case your system does + not really guarantee that the page is persisted to disk in its entirety, you + may run into data corruption. + + + + diff --git a/src/bin/pg_rewind/libpq_source.c b/src/bin/pg_rewind/libpq_source.c index 011c9cce6e..ad7f745c06 100644 --- a/src/bin/pg_rewind/libpq_source.c +++ b/src/bin/pg_rewind/libpq_source.c @@ -132,15 +132,23 @@ init_libpq_conn(PGconn *conn) PQclear(res); /* - * Also check that full_page_writes is enabled. We can get torn pages if - * a page is modified while we read it with pg_read_binary_file(), and we - * rely on full page images to fix them. + * If ensure_full_page_writes is true (the default), check that + * full_page_writes is enabled. The goal here is to not run into a torn + * page. Torn page can happend if a page is modified while we read it + * with pg_read_binary_file(). Some file systems are immune to torn page, + * this is why there is an option to disable this check. Outside of those + * specific systems, we rely on full_page_writes to avoid it. */ - str = run_simple_query(conn, "SHOW full_page_writes"); - if (strcmp(str, "on") != 0) - pg_fatal("full_page_writes must be enabled in the source server"); + if (ensure_full_page_writes) + { + str = run_simple_query(conn, "SHOW full_page_writes"); + if (strcmp(str, "on") != 0) + pg_fatal("full_page_writes is currently disabled on the " + "source server, use the option --no-ensure-full" + "-page-write to bypass this check if you kown " + "what you are doing"); + } pg_free(str); - /* Prepare a statement we'll use to fetch files */ res = PQprepare(conn, "fetch_chunks_stmt", "SELECT path, begin,\n" diff --git a/src/bin/pg_rewind/pg_rewind.c b/src/bin/pg_rewind/pg_rewind.c index 3cd77c09b1..4307d984fa 100644 --- a/src/bin/pg_rewind/pg_rewind.c +++ b/src/bin/pg_rewind/pg_rewind.c @@ -68,6 +68,7 @@ bool showprogress = false; bool dry_run = false; bool do_sync = true; bool restore_wal = false; +bool ensure_full_page_writes = true; /* Target history */ TimeLineHistoryEntry *targetHistory; @@ -86,23 +87,24 @@ usage(const char *progname) printf(_("%s resynchronizes a PostgreSQL cluster with another copy of the cluster.\n\n"), progname); printf(_("Usage:\n %s [OPTION]...\n\n"), progname); printf(_("Options:\n")); - printf(_(" -c, --restore-target-wal use restore_command in target configuration to\n" - " retrieve WAL files from archives\n")); - printf(_(" -D, --target-pgdata=DIRECTORY existing data directory to modify\n")); - printf(_(" --source-pgdata=DIRECTORY source data directory to synchronize with\n")); - printf(_(" --source-server=CONNSTR source server to synchronize with\n")); - printf(_(" -n, --dry-run stop before modifying anything\n")); - printf(_(" -N, --no-sync do not wait for changes to be written\n" - " safely to disk\n")); - printf(_(" -P, --progress write progress messages\n")); - printf(_(" -R, --write-recovery-conf write configuration for replication\n" - " (requires --source-server)\n")); - printf(_(" --config-file=FILENAME use specified main server configuration\n" - " file when running target cluster\n")); - printf(_(" --debug write a lot of debug messages\n")); - printf(_(" --no-ensure-shutdown do not automatically fix unclean shutdown\n")); - printf(_(" -V, --version output version information, then exit\n")); - printf(_(" -?, --help show this help, then exit\n")); + printf(_(" -c, --restore-target-wal use restore_command in target configuration to\n" + " retrieve WAL files from archives\n")); + printf(_(" -D, --target-pgdata=DIRECTORY existing data directory to modify\n")); + printf(_(" --source-pgdata=DIRECTORY source data directory to synchronize with\n")); + printf(_(" --source-server=CONNSTR source server to synchronize with\n")); + printf(_(" -n, --dry-run stop before modifying anything\n")); + printf(_(" -N, --no-sync do not wait for changes to be written\n" + " safely to disk\n")); + printf(_(" -P, --progress write progress messages\n")); + printf(_(" -R, --write-recovery-conf write configuration for replication\n" + " (requires --source-server)\n")); + printf(_(" --config-file=FILENAME use specified main server configuration\n" + " file when running target cluster\n")); + printf(_(" --debug write a lot of debug messages\n")); + printf(_(" --no-ensure-shutdown do not automatically fix unclean shutdown\n")); + printf(_(" --no-ensure-full-page-writes do not make sure that full_page_writes is on\n")); + printf(_(" -V, --version output version information, then exit\n")); + printf(_(" -?, --help show this help, then exit\n")); printf(_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT); printf(_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL); } @@ -118,7 +120,8 @@ main(int argc, char **argv) {"source-pgdata", required_argument, NULL, 1}, {"source-server", required_argument, NULL, 2}, {"no-ensure-shutdown", no_argument, NULL, 4}, - {"config-file", required_argument, NULL, 5}, + {"no-ensure-full-page-writes", no_argument, NULL, 5}, + {"config-file", required_argument, NULL, 6}, {"version", no_argument, NULL, 'V'}, {"restore-target-wal", no_argument, NULL, 'c'}, {"dry-run", no_argument, NULL, 'n'}, @@ -207,6 +210,10 @@ main(int argc, char **argv) break; case 5: + ensure_full_page_writes = false; + break; + + case 6: config_file = pg_strdup(optarg); break; diff --git a/src/bin/pg_rewind/pg_rewind.h b/src/bin/pg_rewind/pg_rewind.h index 80c276285a..f63426256a 100644 --- a/src/bin/pg_rewind/pg_rewind.h +++ b/src/bin/pg_rewind/pg_rewind.h @@ -23,6 +23,7 @@ extern char *datadir_target; extern bool showprogress; extern bool dry_run; extern bool do_sync; +extern bool ensure_full_page_writes; extern int WalSegSz; /* Target history */ -- 2.38.1