![Below are some PSQL (Postgres’s SQL) commands for beginners to getting started with PostgreSQL. 1. Connecting to PostgreSQL database server. psql -U username -h hostname -d databasename. e.g. [postgres@demunix ~]$ psql -U huzefa -h localhost -d postgres Password for user huzefa: psql (10.11) Type "help" for help. postgres=>. Harvester fcu](/img/512x512/1160929635104.webp)
In this command, postgres is the default database of a PostgreSQL server. Connecting to the PostgreSQL server will grant you a session. A session is log-lived, allowing you to perform many requests such as executing commands, before eventually disconnecting. Third, execute the following command to retrieve the PostgreSQL version:In the world of database management, efficiency is key. As databases grow larger and more complex, finding ways to streamline operations becomes crucial. One powerful tool that can...The PostgreSQL query planner relies on statistical information about the contents of tables in order to generate good plans for queries. These statistics are gathered by the ANALYZE command, which can be invoked by itself or as an optional step in VACUUM.It is important to have reasonably accurate statistics, otherwise poor choices …The syntax for using the SELECT statement is as follows: Syntax: SELECT select_list FROM table_name; Now, let’s evaluate the SELECT statement in more detail, Firstly, we need to specify a particular column or a list of columns from where the data is to be retrieved. Commas are used to separate multiple columns, if a list of column is selected ...2. Step Wise below. Opening the Port - Make sure the PSQL Port is open to all remote connections or connections from a specific set of IPs as per your requirement. PSQL, in general, runs at port 5432, and it is configurable, so expose relevant Port accordingly. Update Remote Server PSQL Configuration - Set …SQL Commands This part contains reference information for the SQL commands supported by PostgreSQL . By “ SQL ” the language in general is meant; information about the standards conformance and compatibility of each command can be found on the respective reference page.Connecting to PostgreSQL using psql. To connect to PostgreSQL from the command line, follow these steps: Log in to your A2 Hosting account using SSH. At the command line, type the following command. Replace dbname with the name of the database, and username with the database username: At the Password prompt, type the database …236. You can use PostgreSQL's interactive terminal Psql to show tables in PostgreSQL. 1. Start Psql. Usually you can run the following command to enter into psql: psql DBNAME USERNAME. For example, psql template1 postgres. One situation you might have is: suppose you login as root, and you don't remember the database name.Feb 8, 2024 · This part contains reference information for PostgreSQL client applications and utilities. Not all of these commands are of general utility; some might require special privileges. The common feature of these applications is that they can be run on any host, independent of where the database server resides. When specified on the command line ... All the forms of ALTER TABLE that act on a single table, except RENAME, SET SCHEMA, ATTACH PARTITION, and DETACH PARTITION can be combined into a list of multiple alterations to be applied together. For example, it is possible to add several columns and/or alter the type of several columns in a single command.PostgreSQL Commands. Create User. Create a Database. Connect to a PostgreSQL Database. List Available PostgreSQL Databases. Switch the connection to a new …If you’re in the market for a Jeep Commander and prefer to buy directly from the owner, you’re in luck. In this ultimate guide, we’ll explore the best strategies for finding a Jeep...8th February 2024: PostgreSQL 16.2, 15.6, 14.11, 13.14, and 12.18 Released! Documentation → PostgreSQL 16. ... Executing a Command with a Single-Row Result 43.5.4. Executing Dynamic Commands 43.5.5. Obtaining the Result Status 43.5.6. Doing Nothing At All 43.6. Control Structures5.1. Table Basics #. A table in a relational database is much like a table on paper: It consists of rows and columns. The number and order of the columns is fixed, and each column has a name. The number of rows is variable — it reflects how much data is stored at a given moment. SQL does not make any guarantees about the order of the …You have a Postgres instance (A), and you use postgres_fdw to access data on the Postgres instance (B), which is a remote instance. You then run queries combining data from instances A and B at the database rather than the application level. Get postgres_fdw by running the below command from your …Essential Meta-commands. In my experience with PostgreSQL over the last few years, particularly coming from many years of SQL Server work, learning how to effectively use basic commands in psql has proven to be useful and time saving. Below are the initial set of commands that will help you navigate the PostgreSQL cluster and databases.Running the PostgreSQL interactive terminal program, called psql, which allows you to interactively enter, edit, and execute SQL commands.For example, you’d enter the docker pull postgres:14.5 command if you prefer postgres v14.5. Generally, we recommend using a specific version of Postgres. The :latest version automatically changes with each new Postgres release — and it’s hard to know if those newer versions will introduce breaking changes or vulnerabilities.The command prompt, also known as the command line or CMD, is a powerful tool that allows users to interact with their computer’s operating system through text-based commands. One ...The start sub-command starts a new PostgreSQL server instance in the background. The command tries to find the data directory through the -D option or the PGDATA environment variable. Furthermore, we may set a log file using the -l option: $ sudo -u postgres pg_ctl start -D /var/lib/pgsql/ data -l postgresql.log. Documentation . View the manual. Manuals . You can view the manual for an older version or download a PDF of a manual from the below table. Documentation . View the manual. Manuals . You can view the manual for an older version or download a PDF of a manual from the below table.psql commands. Getting help. Run in PostgreSQL console. # PostgreSQL Working. Recon. Show version. SHOW SERVER_VERSION; Show system status. \conninfo. …Follow the steps below to run a PostgreSQL container: 1. Create a new directory and move to it: mkdir postgres && cd postgres. 2. Create a new docker-compose.yml file with a text editor of your choice (in this example, we used nano ): nano docker-compose.yml. 3. Add the following content to the docker …postgresql. Hi Guys, In this Blog, I'm going to share some basic commands that are useful for a developer in daily use. I give you a list of simple psql commands that supports you query data from PostgreSQL database. 1. Connect to the PostgreSQL database. This command helps you to connect with the …Notes. The utility command pg_ctl can be used to start and shut down the postgres server safely and comfortably.. If at all possible, do not use SIGKILL to kill the main postgres server. Doing so will prevent postgres from freeing the system resources (e.g., shared memory and semaphores) that it holds before terminating. This might …This command sets the current user identifier of the current SQL session to be role_name. The role name can be written as either an identifier or a string literal. After SET ROLE, permissions checking for SQL commands is carried out as though the named role were the one that had logged in originally. The …5.1. Table Basics #. A table in a relational database is much like a table on paper: It consists of rows and columns. The number and order of the columns is fixed, and each column has a name. The number of rows is variable — it reflects how much data is stored at a given moment. SQL does not make any guarantees about the order of the …The PostgreSQL query planner relies on statistical information about the contents of tables in order to generate good plans for queries. These statistics are gathered by the ANALYZE command, which can be invoked by itself or as an optional step in VACUUM.It is important to have reasonably accurate statistics, otherwise poor choices …The syntax for using the SELECT statement is as follows: Syntax: SELECT select_list FROM table_name; Now, let’s evaluate the SELECT statement in more detail, Firstly, we need to specify a particular column or a list of columns from where the data is to be retrieved. Commas are used to separate multiple columns, if a list of column is selected ...sudo service postgresql-9.3 start. Log on to the psql command-line tool by running the command: sudo -u postgres psql. Run a CREATE DATABASE command to create a ...This parameter can only be set in the postgresql.conf file or on the server command line. syslog_ident (string) # When logging to syslog is enabled, this parameter determines the program name used to identify PostgreSQL messages in syslog logs. The default is postgres. This parameter can only be set in the …In Postgres, the “\dn”, “\dn+” commands, and “information_schema” are used to get the list of available schemas. The “\dn” and “\dn+” commands must be executed from the SQL Shell; however, getting the list of available schemas using “information_schema” can be accomplished from any interface like pgAdmin or psql.Jun 10, 2023 · Enter the following command to access the PostgreSQL prompt: psql -U <username> -d <database_name>. Replace <username> with your PostgreSQL username and <database_name> with the name of the database you want to connect to. If you’re connecting to the default database, you can omit the -d <database_name> part. PostgreSQL instead requires each session to issue its own CREATE TEMPORARY TABLE command for each temporary table to be used. This allows different sessions to use the same temporary table name for different purposes, whereas the standard's approach constrains all instances of a given temporary table name to have the same table …The SQL Language. This part describes the use of the SQL language in PostgreSQL. We start with describing the general syntax of SQL, then explain how to create the structures to hold data, how to populate the database, and how to query it. The middle part lists the available data types and functions for use in SQL commands.Description. createdb creates a new PostgreSQL database.. Normally, the database user who executes this command becomes the owner of the new database. However, a different owner can be specified via the -O option, if the executing user has appropriate privileges.. createdb is a wrapper around the SQL command CREATE DATABASE.There is …This part contains reference information for PostgreSQL client applications and utilities. Not all of these commands are of general utility; some might require special privileges. The common feature of these applications is that they can be run on any host, independent of where the database server resides. When specified on the command line ...In Postgres, the “\dn”, “\dn+” commands, and “information_schema” are used to get the list of available schemas. The “\dn” and “\dn+” commands must be executed from the SQL Shell; however, getting the list of available schemas using “information_schema” can be accomplished from any interface like pgAdmin or psql.SELECT c1, c2 FROM t; Create a new view that consists of c1 and c2. CREATE VIEW v(c1,c2) AS.Unity of command is a military principle that has been applied to business. It follows the idea that a subordinate should have only one person to whom they are directly responsible...SQL Shell (psql) is a terminal based program where you can write and execute SQL syntax in the command-line terminal. Open SQL Shell (psql). You will find the ...Jun 10, 2023 · Enter the following command to access the PostgreSQL prompt: psql -U <username> -d <database_name>. Replace <username> with your PostgreSQL username and <database_name> with the name of the database you want to connect to. If you’re connecting to the default database, you can omit the -d <database_name> part. Sep 29, 2016 · postgres=# help You are using psql, the command-line interface to PostgreSQL. Type: \copyright for distribution terms \h for help with SQL commands \? for help with psql commands \g or terminate with semicolon to execute query \q to quit Create a schema called test in the default database called postgres Command and Conquer is a legendary real-time strategy game that has captured the hearts of gamers for decades. With its intricate gameplay mechanics and strategic depth, it offers ...We gathered a list of handy PostgreSQL commands and queries when working with PostgreSQL databases. Please ping us @ForestAdmin if you’d like to add something to the cheat sheet! Getting started with PostgreSQL Login and enter PostgreSQL command line utility psql $ sudo su - postgres psqlPostgreSQL Downloads. PostgreSQL is available for download as ready-to-use packages or installers for various platforms, as well as a source code archive if you want to build it yourself. Packages and Installers. Select your operating system family: Linux macOS Windows BSD SolarisFeb 8, 2024 · This part contains reference information for PostgreSQL client applications and utilities. Not all of these commands are of general utility; some might require special privileges. The common feature of these applications is that they can be run on any host, independent of where the database server resides. When specified on the command line ... Feb 8, 2024 · Specifies that VACUUM should attempt to process the corresponding TOAST table for each relation, if one exists. This is usually the desired behavior and is the default. Setting this option to false may be useful when it is only necessary to vacuum the main relation. This option is required when the FULL option is used. Jun 13, 2023 · 「PostgreSQLのpsqlコマンド」について学びたいですか？この記事では、psqlコマンドの基本的な使い方や実践的な例を詳細に解説しています。たくさんのコマンド例を用意しているので、内容は視覚的にも理解しやすいです。初めての方でも安心してご覧いただけます。 Feb 8, 2024 · Specifies that VACUUM should attempt to process the corresponding TOAST table for each relation, if one exists. This is usually the desired behavior and is the default. Setting this option to false may be useful when it is only necessary to vacuum the main relation. This option is required when the FULL option is used. SQL Commands. This part contains reference information for the SQL commands supported by PostgreSQL. By “SQL” the language in general is meant; information about …The Command Prompt is a powerful tool that comes built-in with every Windows operating system. While it may seem intimidating at first, mastering the Command Prompt can greatly enh...2. Step Wise below. Opening the Port - Make sure the PSQL Port is open to all remote connections or connections from a specific set of IPs as per your requirement. PSQL, in general, runs at port 5432, and it is configurable, so expose relevant Port accordingly. Update Remote Server PSQL Configuration - Set …What you want to do is preform the logon first ( psql -U postgres -d ticketon -c) and then pipe via STDIN the query you wish to preform ( "UPDATE "user" SET "password" = 'test'" ). In bash this will be the following: echo "UPDATE "user" SET "password" = 'test'" | psql -U postgres -d ticketon -c. The above could work …A CREATE FUNCTION command is defined in the SQL standard. The PostgreSQL implementation can be used in a compatible way but has many extensions. Conversely, the SQL standard specifies a number of optional features that are not implemented in PostgreSQL. The following are important …Connect to a PostgreSQL server using the PostgreSQL command-line client (psql) and a username. It will prompt you for the password: psql -U username To connect to a specific dat abase on a PostgreSQL server with a username: psql-U username -h host_name -d d atabase_name To exit the client: \q For a full list of comma nds: \h For a list of psql ...1. You can use psql on CMD on Windows 11. First, search and click Edit the system environment variables as shown below: Then, click Environment Variables as shown below: Lastly, set C:\Program Files\PostgreSQL\<version>\bin to Path either in User variables or System variables or both as shown below.Golang library: Postgres commands (pg_restore, pg_dumpg) Topics. golang postgresql Resources. Readme License. MIT license Activity. Custom properties. Stars. 45 stars Watchers. 3 watching Forks. 15 forks Report repository Releases 9. v0.6.1 Latest Mar 3, 2023 + 8 releases Packages 0. No packages published . Contributors 8.8th February 2024: PostgreSQL 16.2, 15.6, 14.11, 13.14, and 12.18 Released! Documentation → PostgreSQL 16. ... Executing a Command with a Single-Row Result 43.5.4. Executing Dynamic Commands 43.5.5. Obtaining the Result Status 43.5.6. Doing Nothing At All 43.6. Control StructuresI have postgres installed on an ubuntu machine, and I am able to enter into the command line via something along the lines of: $ sudo -u postgres psql psql (10.15 (Ubuntu 10.15-0ubuntu0.18.04.1)) T...9. It doesn't look like psql supports traditional end-of-line -- comments in its psql -specific "slash commands." -- these are called meta-commands in the PostgreSQL psql documentation. However, if you're okay with the end-of-line comments being displayed on execution, using \echo seems to be a valid work-around.Specifies that VACUUM should attempt to process the corresponding TOAST table for each relation, if one exists. This is usually the desired behavior and is the default. Setting this option to false may be useful when it is only necessary to vacuum the main relation. This option is required when the FULL option is used.The -C, or --create, command will try to create a postgrelearning database. If one exists, you’ll get an error, so, you can again modify the pg_restore command: 1. pg_restore -d postgres -U postgres -C -c bucustom.dmp. Running both --clean and --create will result in pg_restore dropping and recreating your database.May 15, 2023 ... Introduction to Postgres Command-Line · Options: When connecting to the psql database, you can use various options such as -a, -b, -c, -d, etc. The full set of command-line arguments and meta-commands are described in a subsequent section. There are some environment variables which can be used in liu of command line arguments. Additionally, the Postgres frontend library used by the psql application looks for other optional environment variables to configure, for example, the style of ... COPY moves data between PostgreSQL tables and standard file-system files. COPY TO copies the contents of a table to a file, while COPY FROM copies data from a file to a table (appending the data to whatever is in the table already). COPY TO can also copy the results of a SELECT query. If a column list is specified, COPY TO copies only the data ...Heroku Postgres is integrated directly into the Heroku CLI and offers many helpful commands that simplify common database tasks. pg:info. To see all PostgreSQL databases provisioned by your application and the identifying characteristics of each (such as database size, status, number of tables, and PG version), use the heroku pg:info …Section 6. PostgreSQL Tips. Reset Password – show you how to reset the forgotten password of the postgres user. psql Commands – give you the most common psql command to help you query data from PostgreSQL faster and more effectively. Describe Table – get information on a particular table.Summary: in this tutorial, you are going to learn how to use the basic PostgreSQL SELECT statement to query data from a table.. Note that if you don’t know how to execute a query against the PostgreSQL database using the psql command-line tool or pgAdmin GUI tool, you can check the connection to the PostgreSQL database tutorial.. One of the most …The command prompt, also known as the command line or CMD, is a powerful tool that allows users to interact with their computer’s operating system through text-based commands. One ...Google Home is a voice-activated assistant that can help you control your home. Google Home is a voice-activated assistant that can help you control your home. Using it is simple —...postgres= #. A good first command to test and get your bearings is \l. This lists the databases available on the PostgreSQL server you’re connected to: \l. The command produces output in a tabular format, showing the name of each database along with its owner and other attributes. You can connect to a different database using the \c command ...SQL Commands. This part contains reference information for the SQL commands supported by PostgreSQL. By “SQL” the language in general is meant; information about the standards conformance and compatibility of each command can be found on the respective reference page.Learn how to use psql, a tool that lets you interact with PostgreSQL databases through a terminal interface. Find out how to create, list, switch, and delete databases, and how to get help and quit …Feb 8, 2024 · Description. pg_restore is a utility for restoring a PostgreSQL database from an archive created by pg_dump in one of the non-plain-text formats. It will issue the commands necessary to reconstruct the database to the state it was in at the time it was saved. The archive files also allow pg_restore to be selective about what is restored, or ... The following command-line options control the content and format of the output. dbname. ... $ pg_restore -d postgres --clean --create db.dump. To dump a single table named mytab: $ pg_dump -t mytab mydb > db.sql. To dump all tables whose names start with emp in the detroit schema, ...Specifies that VACUUM should attempt to process the corresponding TOAST table for each relation, if one exists. This is usually the desired behavior and is the default. Setting this option to false may be useful when it is only necessary to vacuum the main relation. This option is required when the FULL option is used.5.1. Table Basics #. A table in a relational database is much like a table on paper: It consists of rows and columns. The number and order of the columns is fixed, and each column has a name. The number of rows is variable — it reflects how much data is stored at a given moment. SQL does not make any guarantees about the order of the …26.3.7. Caveats. As with everything that contains valuable data, PostgreSQL databases should be backed up regularly. While the procedure is essentially simple, it is important to have a clear understanding of the underlying techniques and assumptions. There are three fundamentally different approaches to backing up PostgreSQL data:Below are some PSQL (Postgres’s SQL) commands for beginners to getting started with PostgreSQL. 1. Connecting to PostgreSQL database server. psql -U username -h hostname -d databasename. e.g. [postgres@demunix ~]$ psql -U huzefa -h localhost -d postgres Password for user huzefa: psql (10.11) Type "help" for help. postgres=>Jul 31, 2018 · Open "SQL Shell (psql)" from your Applications (Mac). Click enter for the default settings. Enter the password when prompted. *) Type \conninfo to see which user you are connected as. *) Type \l to see the list of Databases. *) Connect to a database by \c <Name of DB>, for example \c GeneDB1. Sep 28, 2021 · In this article, we will look into some of the most frequently used Psql commands. The below table provides with the frequently used Psql commands: Command. Description. Additional Information. psql -d database -U user -W. Connects to a database under a specific user. -d: used to state the database name. -U:used to state the database user. This part contains reference information for PostgreSQL client applications and utilities. Not all of these commands are of general utility; some might require special privileges. The common feature of these applications is that they can be run on any host, independent of where the database server resides. When specified on the command line ...PostgreSQL’s ‘psql’ offers even more advanced options for command history management: > SELECT. < \g. If you hit Enter after ‘<‘ or ‘>’, ‘psql’ will display the previous or next command containing ‘SELECT’. \s filename. Save your history to a specific file for later review or sharing. \i filename. You can run all commands ...This command sets the current user identifier of the current SQL session to be role_name. The role name can be written as either an identifier or a string literal. After SET ROLE, permissions checking for SQL commands is carried out as though the named role were the one that had logged in originally. The …Description. psql is a terminal-based front-end to PostgreSQL. It enables you to type in queries interactively, issue them to PostgreSQL, and see the query results. Alternatively, input can be from a file or from command line arguments. Golang library: Postgres commands (pg_restore, pg_dumpg) Topics. golang postgresql Resources. Readme License. MIT license Activity. Custom properties. Stars. Like other terminal client applications, psql offers a wide range of commands to interact with PostgreSQL databases. However, below I tried to present the 10 commands that by far I use the most on a daily basis. # 1 Connect To PostgreSQL Database. The first step to interact with a PG database is connecting to it.The Ten Commandments are a set of laws given to the Jewish people in the Old Testament. In Exodus 20, the Bible says that God himself spoke the Ten Commandments to Moses on Mount S...PostgreSQL Commands. Connecting to PostgreSQL. When we install Postgres on our servers, a new user by the name ‘postgres’ is also created along with the installation. So when we are to connect to the PostgreSQL server, we will switch to this user & than connect the database,
1. Command to list all commands available in PostgreSQL. The ‘\?’ command returns all of the commands available in PostgreSQL. Illustrate the result of …. Principal com welcome
In Postgres, an SQL command: “\dt”, and built-in schemas: pg_catalog and information_schema, are used to list all the tables of a database. The “\dt” or “\dt+” commands will be executed from the SQL Shell psql, however, you can run the pg_catalog or information_schema from any interface of your choice, such …Learn how to use psql, the terminal-based interface of PostgreSQL, to interact with databases efficiently. Discover 10 useful psql commands for listing, switching, …The command prompt, also known as the command line or CMD, is a powerful tool that allows users to interact with their computer’s operating system through text-based commands. One ...SQL Commands. This part contains reference information for the SQL commands supported by PostgreSQL. By “SQL” the language in general is meant; information about the standards conformance and compatibility of each command can be found on the respective reference page.Golang library: Postgres commands (pg_restore, pg_dumpg) Topics. golang postgresql Resources. Readme License. MIT license Activity. Custom properties. Stars. 45 stars Watchers. 3 watching Forks. 15 forks Report repository Releases 9. v0.6.1 Latest Mar 3, 2023 + 8 releases Packages 0. No packages published . Contributors 8.CLUSTER instructs PostgreSQL to cluster the table specified by table_name based on the index specified by index_name. The index must already have been defined on table_name. When a table is clustered, it is physically reordered based on the index information. Clustering is a one-time operation: when the table is subsequently …9. It doesn't look like psql supports traditional end-of-line -- comments in its psql -specific "slash commands." -- these are called meta-commands in the PostgreSQL psql documentation. However, if you're okay with the end-of-line comments being displayed on execution, using \echo seems to be a valid work-around. What is psql Psql is the interactive terminal for working with Postgres. Theres an abundance of flags available for use when working with psql, but lets focus on some of the most important ones, then how to connect: -h the host to connect to -U the user to connect with -p the port to connect to (default is 5432) psql -h localhost -U username databasename PostgreSQL’s ‘psql’ offers even more advanced options for command history management: > SELECT. < \g. If you hit Enter after ‘<‘ or ‘>’, ‘psql’ will display the previous or next command containing ‘SELECT’. \s filename. Save your history to a specific file for later review or sharing. \i filename. You can run all commands ...Feb 8, 2024 · To start a single-user mode server, use a command like. postgres --single -D /usr/local/pgsql/data other-options my_database. Provide the correct path to the database directory with -D, or make sure that the environment variable PGDATA is set. Also specify the name of the particular database you want to work in. Commands like dropdb should be entered OUTSIDE psql. What i had been doing was: $ psql postgres. postgres=# dropdb databasename. Notice the first command is in Bash and fires psql, and the second is sent within psql. The correct way is to send the command directly in bash (the console): $ dropdb …Based on PostgreSQL 11 Beta 1 Released!: User Experience Enhancements. Another feature that fell into this category was the inability to intuitively quit from the PostgreSQL command-line (psql). There has been numerous recorded complaints of users trying to quit with the quit and exit commands, only to learn that the …Feb 8, 2024 · Description. psql is a terminal-based front-end to PostgreSQL. It enables you to type in queries interactively, issue them to PostgreSQL, and see the query results. Alternatively, input can be from a file or from command line arguments. sudo apt update. Then, install the Postgres package along with a -contrib package that adds some additional utilities and functionality: sudo apt install postgresql postgresql-contrib. Ensure that the server is running using the systemctl start command: sudo systemctl start postgresql.service.1. Creating a User in PostgreSQL. To create a database named "db_user", connect to the PostgreSQL database server using a user with sufficient privileges (such as the "postgres" user or a superuser) and run the following command: postgres=# CREATE USER db_user; CREATE ROLE. -- Set a password for the user.Meta-Commands. Anything you enter in psql that begins with an unquoted backslash is a psql meta-command that is processed by psql itself. These commands make psql more useful for administration or scripting. Meta-commands are often called slash or backslash commands. The format of a psql command …Apr 29, 2023 ... sudo su - postgres is a command used to run a specific command as the postgres user. After entering this command, type 'psql' to enter the ...26.3.7. Caveats. At all times, PostgreSQL maintains a write ahead log (WAL) in the pg_wal/ subdirectory of the cluster's data directory. The log records every change made to the database's data files. This log exists primarily for crash-safety purposes: if the system crashes, the database can be restored to ….