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Restoring PostgreSQL Data on CVMs

Last updated: 2022-04-11 16:24:10

    When data is lost or corrupted, you can use the instance clone feature to restore data to a specific time point within the log retention period.

    Downloading Backup in Console for Restoration

    1. Install PostgreSQL

    In the CVM instance where data is to be restored to, install PostgreSQL on the same version as that of the backup data. If PostgreSQL has already been installed, skip this step.

    Note:

    This document shows you how to install PostgreSQL 10 and restore data in a CentOS 7 CVM instance.

    1. Log in to the Linux CVM instance. For more information, see Customizing Linux CVM Configurations.
    2. Install PostgreSQL. The yum repository method is used in this document. You can click here to find the needed yum repository.
      Note:

      To restore backup data of PostgreSQL v11.8 or 12.4, you need to modify the version number in the installation package name to install PostgreSQL on the same version as that of the backup data. For example, replace postgresql10-server with postgresql11-server or postgresql12-server.

      Run the following command to install PostgreSQL 10:
    yum install https://download.postgresql.org/pub/repos/yum/reporpms/EL-7-x86_64/pgdg-redhat-repo-latest.noarch.rpm
    yum install postgresql10-server postgresql10-contrib postgresql10 postgresql10.x86_64
    
    Note:

    The command for installing PostgreSQL 9.5 is as follows:

    >yum install https://yum.postgresql.org/9.5/redhat/rhel-7.6-x86_64/pgdg-centos95-9.5-3.noarch.rpm
    yum install postgresql95-server postgresql95-contrib postgresql95
    
    
    						

    1. Run the following command to check the installation result:
      rpm -aq| grep postgres
      

    A message similar to the following will be returned:

    [root@i-87-575-VM vmuser]# rpm -aq| grep postgres
    postgresql10-libs-10.11-2PGDG.rhel7.x86_64
    postgresql10-server-10.11-2PGDG.rhel7.x86_64
    postgresql10-contrib-10.11-2PGDG.rhel7.x86_64
    postgresql10-10.11-2PGDG.rhel7.x86_64
    

    2. Create a restoration directory as the postgres user

    Switch to the postgres user and create a restoration directory in the CVM instance.

    mkdir /var/lib/pgsql/10/recovery
    

    recovery is a sample directory name, which can be modified as needed. In the following examples, the directory names will be the same for one major version. For example, the directory will be /var/lib/pgsql/10 for PostgreSQL 10.x and /var/lib/pgsql/9.5 for PostgreSQL 9.5.x.

    Note:

    The command for PostgreSQL 9.5 is as follows:

    mkdir /var/lib/pgsql/9.5/recovery
    

    3. Download the full backup file

    1. Log in to the TencentDB for PostgreSQL console. In the instance list, click Manage in the Operation column to enter the management page.
    2. On the Backup Management tab, locate the backup to be restored based on backup time in the backup list and click Download in the Operation column.
    3. Download the backup file from the provided VPC address or public network address.
      Note:

      • If a VPC address is to be used, the TencentDB instance and CVM instance should be in the same VPC, and the backup needs to be downloaded to the /var/lib/pgsql/10/recovery directory.
      • If a public network address is to be used, the downloaded backup file needs to be uploaded to the /var/lib/pgsql/10/recovery directory in the CVM instance. For more information, see Copying Local Files to CVMs.
      After upload, the following information will be displayed:

    4. Decompress the full backup file

    Run the following command to decompress the full backup file:

    cd /var/lib/pgsql/10/recovery
    tar -xf 20191221010146.tar.gz
    

    After decompression, the following information will be displayed:

    5. Remove unnecessary temporary files

    Run the following command to remove unnecessary temporary files:

    rm -rf backup_label
    

    6. Modify the configuration file

    1. Use # at the beginning of a line to comment out the following options in the postgresql.conf configuration file.
      Comment all out if there is more than one such option.
    shared_preload_libraries
    local_preload_libraries
    pg_stat_statements.max
    pg_stat_statements.track
    archive_mode
    archive_command
    synchronous_commit
    synchronous_standby_names
    
    Note:

    To restore backup data of PostgreSQL v12.4, include = 'standby.conf' also needs to be commented out.
    2. Modify the postgresql.conf configuration file.

    port = '5432'    ## Change the value of the `port` parameter to 5432
    unix_socket_directories = '/var/run/postgresql/'  ## Change the value of `unix_socket_directories` to `/var/run/postgresql/`. This step can be skipped if the value is not set
    
    1. Append configurations to the postgresql.conf configuration file, indicating that the strong sync mode will no longer be used.
    synchronous_commit = local
    synchronous_standby_names = ''
    

    7. Modify folder permissions as the root user

    chmod 0700 /var/lib/pgsql/10/recovery
    chown postgres:postgres /var/lib/pgsql/10/recovery -R
    

    After modification, the following information will be displayed:

    8. Use the incremental backup file (optional)

    If this step is skipped, the content of the database will be that when the full backup was started.
    Put the xlog files in the /var/lib/pgsql/10/recovery/pg_wal folder. If the downloaded backup does not contain the pg_wal directory, modify pg_xlog to pg_wal, and PostgreSQL will automatically replay the xlog files.
    For example, if a full backup is started at 12:00 and all xlog files between 12:00 and 13:00 are put in the pg_wal folder, then data can be restored to 13:00.

    Note:

    For PostgreSQL 9.x, the folder is /var/lib/pgsql/9.x/recovery/pg_xlog.

    1. On the Backup Management page in the console, get the xlog download address and download the incremental backup file (xlog).
      After download, the following information will be displayed:
    2. Decompress the log to the pg_wal folder.
    tar -xf 20170904010214_20170905010205.tar.gz
    

    9. Start PostgreSQL as the postgres user

    /usr/pgsql-10/bin/pg_ctl start -D /var/lib/pgsql/10/recovery
    

    10. Log in to PostgreSQL

    1. Log in to PostgreSQL.
    export PGDATA=/var/lib/pgsql/10/recovery
    psql
    


    2. Check whether the database is running.

    /usr/pgsql-10/bin/pg_ctl status -D /var/lib/pgsql/10/recovery
    

    If the prompt is "server is running", the database is running.

    Manually Exporting Data for Restoration

    You can also manually export backup data and then restore it in the CVM instance. This scheme is applicable to both Windows and Linux regardless of the file system where physical files reside.

    1. Dump the data from the CVM instance as shown below:
    Command format: pg_dump -h <access IP> -U <accessing user> -f <full path of the backup file> -c -C <name of the exported database>
    Example:
    /usr/pgsql-10/bin/pg_dump -h 192.168.0.16 -U testroot -f backup.sql -c -C postgres
    
    • If no file format is specified, a text file will be exported by default as shown below:
    -- PostgreSQL database dump
    --
    -- Dumped from database version 9.5.4
    -- Dumped by pg_dump version 9.5.19
    SET statement_timeout = 0;
    SET lock_timeout = 0;
    SET client_encoding = 'UTF8';
    SET standard_conforming_strings = on;
    SELECT pg_catalog.set_config('search_path', '', false);
    SET check_function_bodies = false;
    SET xmloption = content;
    SET client_min_messages = warning;
    SET row_security = off;
    
    • If there is a massive amount of data, specify the file format as binary file by using -Fc.
    1. Restore the data in the CVM instance.
    • For text files, data can be restored by running the following SQL statement:
      psql -U postgres <./backup.sql
      
    Note:

    Because there are extensions like pg_stat_error, an error may occur, but that does not affect data import.

    • For binary files, data needs to be restored by using pg_restore.
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