From c8c5d5809b8f75217af84bfc6902a8d8ec066841 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Mon, 22 Apr 2024 14:52:02 -0400 Subject: [PATCH v1] pg_combinebackup: Detect checksum mismatches and document limitation. If not all backups have the same checksum status, but the final backup has checksums enabled, then the output directory may include pages with invalid checksums. Document this limitation and explain how to work around it. In a future release, we may want to teach pg_combinebackup to recompute page checksums when required, but as feature freeze has come and gone, it seems a bit too late to do that for this release. --- doc/src/sgml/backup.sgml | 6 +++++- doc/src/sgml/ref/pg_combinebackup.sgml | 20 +++++++++++++++++++ src/bin/pg_combinebackup/pg_combinebackup.c | 22 +++++++++++++++++++++ 3 files changed, 47 insertions(+), 1 deletion(-) diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml index b3468eea3c..91da3c26ba 100644 --- a/doc/src/sgml/backup.sgml +++ b/doc/src/sgml/backup.sgml @@ -892,7 +892,11 @@ test ! -f /mnt/server/archivedir/00000001000000A900000065 && cp pg_wal/0 only the incremental backup itself but also all earlier backups that are required to supply the blocks omitted from the incremental backup. See for further information about - this requirement. + this requirement. Note that there are restrictions on the use of + pg_combinebackup when the checksum status of the + cluster has been changed; see + pg_combinebackup + limitations. diff --git a/doc/src/sgml/ref/pg_combinebackup.sgml b/doc/src/sgml/ref/pg_combinebackup.sgml index def1e38ae6..fcf3e25460 100644 --- a/doc/src/sgml/ref/pg_combinebackup.sgml +++ b/doc/src/sgml/ref/pg_combinebackup.sgml @@ -261,6 +261,26 @@ PostgreSQL documentation + + Limitations + + + pg_combinebackup does not recompute page checksums when + writing the output directory. Therefore, if any of the backups used for + reconstruction were taken with checksums disabled, but the final backup was + taken with checksums enabled, the resulting directory may contain pages + with invalid checksums. + + + + To avoid this problem, taking a new full backup after changing the checksum + state of the cluster using is + recommended. Otherwise, you can disable and then optionally reenable + checksums on the directory produced by pg_combinebackup + in order to correct the problem. + + + Environment diff --git a/src/bin/pg_combinebackup/pg_combinebackup.c b/src/bin/pg_combinebackup/pg_combinebackup.c index 95da1b01bc..232e16036f 100644 --- a/src/bin/pg_combinebackup/pg_combinebackup.c +++ b/src/bin/pg_combinebackup/pg_combinebackup.c @@ -583,6 +583,8 @@ check_control_files(int n_backups, char **backup_dirs) { int i; uint64 system_identifier = 0; /* placate compiler */ + uint32 data_checksum_version = 0; /* placate compiler */ + bool data_checksum_mismatch = false; /* Try to read each control file in turn, last to first. */ for (i = n_backups - 1; i >= 0; --i) @@ -612,6 +614,16 @@ check_control_files(int n_backups, char **backup_dirs) controlpath, (unsigned long long) system_identifier, (unsigned long long) control_file->system_identifier); + /* + * Detect checksum mismatches, but only if the last backup in the + * chain has checksums enabled. + */ + if (i == n_backups - 1) + data_checksum_version = control_file->data_checksum_version; + else if (data_checksum_version != 0 && + data_checksum_version != control_file->data_checksum_version) + data_checksum_mismatch = true; + /* Release memory. */ pfree(control_file); pfree(controlpath); @@ -624,6 +636,16 @@ check_control_files(int n_backups, char **backup_dirs) pg_log_debug("system identifier is %llu", (unsigned long long) system_identifier); + /* + * Warn the user if not all backups are in the same state with regards to + * checksums. + */ + if (data_checksum_mismatch) + { + pg_log_warning("only some backups have checksums enabled"); + pg_log_warning_hint("disable, and optionally reenable, checksums on the output directory to avoid failures"); + } + return system_identifier; } -- 2.39.3 (Apple Git-145)