Description

lt_verifybackup is used to check the integrity of a database cluster backup taken using lt_basebackup against a backup_manifest generated by the server at the time of the backup. The backup must be stored in the "plain" format; a "tar" format backup can be checked after extracting it.

It is important to note that the validation which is performed by lt_verifybackup does not and cannot include every check which will be performed by a running server when attempting to make use of the backup. Even if you use this tool, you should still perform test restores and verify that the resulting databases work as expected and that they appear to contain the correct data. However, lt_verifybackup can detect many problems that commonly occur due to storage problems or user error.

Backup verification proceeds in four stages. First, lt_verifybackup reads the backup_manifest file. If that file does not exist, cannot be read, is malformed, or fails verification against its own internal checksum, lt_verifybackup will terminate with a fatal error.

Second, lt_verifybackup will attempt to verify that the data files currently stored on disk are exactly the same as the data files which the server intended to send, with some exceptions that are described below. Extra and missing files will be detected, with a few exceptions. This step will ignore the presence or absence of, or any modifications to, lightdb.auto.conf, standby.signal, and recovery.signal, because it is expected that these files may have been created or modified as part of the process of taking the backup. It also won't complain about a backup_manifest file in the target directory or about anything inside lt_wal, even though these files won't be listed in the backup manifest. Only files are checked; the presence or absence of directories is not verified, except indirectly: if a directory is missing, any files it should have contained will necessarily also be missing.

Next, lt_verifybackup will checksum all the files, compare the checksums against the values in the manifest, and emit errors for any files for which the computed checksum does not match the checksum stored in the manifest. This step is not performed for any files which produced errors in the previous step, since they are already known to have problems. Files which were ignored in the previous step are also ignored in this step.

Finally, lt_verifybackup will use the manifest to verify that the write-ahead log records which will be needed to recover the backup are present and that they can be read and parsed. The backup_manifest contains information about which write-ahead log records will be needed, and lt_verifybackup will use that information to invoke lt_waldump to parse those write-ahead log records. The --quiet flag will be used, so that lt_waldump will only report errors, without producing any other output. While this level of verification is sufficient to detect obvious problems such as a missing file or one whose internal checksums do not match, they aren't extensive enough to detect every possible problem that might occur when attempting to recover. For instance, a server bug that produces write-ahead log records that have the correct checksums but specify nonsensical actions can't be detected by this method.

Note that if extra WAL files which are not required to recover the backup are present, they will not be checked by this tool, although a separate invocation of lt_waldump could be used for that purpose. Also note that WAL verification is version-specific: you must use the version of lt_verifybackup, and thus of lt_waldump, which pertains to the backup being checked. In contrast, the data file integrity checks should work with any version of the server that generates a backup_manifest file.

Options

lt_verifybackup accepts the following command-line arguments:

Other options are also available:

Examples

To create a base backup of the server at mydbserver and verify the integrity of the backup:

$ lt_basebackup -h mydbserver -D /usr/local/lightdb-x/data
$ lt_verifybackup /usr/local/lightdb-x/data

To create a base backup of the server at mydbserver, move the manifest somewhere outside the backup directory, and verify the backup:

$ lt_basebackup -h mydbserver -D /usr/local/lightdb-x/backup1234
$ mv /usr/local/lightdb-x/backup1234/backup_manifest /my/secure/location/backup_manifest.1234
$ lt_verifybackup -m /my/secure/location/backup_manifest.1234 /usr/local/lightdb-x/backup1234

To verify a backup while ignoring a file that was added manually to the backup directory, and also skipping checksum verification:

$ lt_basebackup -h mydbserver -D /usr/local/lightdb-x/data
$ edit /usr/local/lightdb-x/data/note.to.self
$ lt_verifybackup --ignore=note.to.self --skip-checksums /usr/local/lightdb-x/data

See Also