gsql

gsql is a database connection tool provided by MogDB and runs in the command-line interface (CLI). Users can use gsql to connect to a server and perform operations and maintenance on the server. In addition to basic functions for performing operations on a database, gsql provides several advanced features for users.

Overview

Basic Features

• Connect to the database: For details, see "Using the gsql Client for Connection" in the Administrator Guide.

  NOTE: If the gsql client is used to connect to a database, the connection timeout period will be 5 minutes by default. If the database has not correctly set up a connection and authenticated the identity of the client within this period, gsql will time out and exit. To resolve this problem, see FAQs.

• Run SQL statements: Interactively entered SQL statements and specified SQL statements in a file can be run.

• Run meta-commands: Meta-commands help the administrator view database object information, query cache information, format SQL output, and connect to a new database. For details about meta-commands, see [Meta-Command Reference](#Meta-Command Reference).

Advanced Features

Table 1 lists the advanced features of gsql.

Table 1 Advanced features of gsql

• Environment variables

  To set a variable, run the \set meta-command of gsql. For example, to set variable foo to bar, run the following command:

  mogdb=# \set foo bar

  To reference the value of a variable, add a colon (:) before the variable. For example, to view the value of variable foo, run the following command:

  mogdb=# \echo :foo
  bar

  The variable reference method is suitable for regular SQL statements and meta-commands.

  gsql pre-defines some special variables and plans the values of these variables. To ensure compatibility with later versions, do not use these variables for other purposes. For details about special variables, see Table 2.

  NOTE:

  • All the special variables consist of upper-case letters, digits, and underscores(_).
  • To view the default value of a special variable, run the \echo : varname meta-command, for example, \echo : DBNAME.

  Table 2 Settings of special variables

  Environment Variable	Setting Method	Description
  DBNAME	\set DBNAME dbname	Name of the connected database. This variable is set again when a database is connected.
  ECHO	`\set ECHO all	queries`
  ECHO_HIDDEN	`\set ECHO_HIDDEN on	off
  ENCODING	\set ENCODING encoding	Character set encoding of the current client.
  FETCH_COUNT	\set FETCH_COUNT *variable*	- If the value is an integer greater than 0, for example, n, n lines will be selected from the result set to the cache and displayed on the screen when the SELECT statement is run. - If this variable is not set or set to a value less than or equal to 0, all results are selected at a time to the cache when the SELECT statement is run. NOTE: A proper variable value helps reduce the memory usage. The recommended value range is from 100 to 1000.
  HOST	\set HOST hostname	Specifies the name of a connected host.
  IGNOREEOF	\set IGNOREEOF variable	- If this variable is set to a number, for example, 10, the first nine EOF characters entered (generally by pressing Ctrl+D) in gsql are ignored and the gsql program exits when Ctrl+D is pressed tenth times. - If this variable is set to a non-numeric value, the default value is 10. - If this variable is deleted, gsql exits when an EOF is entered.
  LASTOID	\set LASTOID oid	Specifies the last OID, which is the value returned by an INSERT or lo_import command. This variable is valid only before the output of the next SQL statement is displayed.
  ON_ERROR_ROLLBACK	`\set ON_ERROR_ROLLBACK on	interactive
  ON_ERROR_STOP	`\set ON_ERROR_STOP on	off`
  PORT	\set PORT port	Specifies the port number of a connected database.
  USER	\set USER username	Specifies the database user you are currently connected as.
  VERBOSITY	`\set VERBOSITY terse	default

• SQL substitution

  gsql, like a parameter of a meta-command, provides a key feature that enables you to substitute a standard SQL statement for a gsql variable. gsql also provides a new alias or identifier for the variable. To replace the value of a variable using the SQL substitution method, add a colon (:) before the variable. For example:

  mogdb=# \set foo 'HR.areaS'
  mogdb=# select * from :foo;
   area_id |       area_name
  ---------+------------------------
         4 | Middle East and Africa
         3 | Asia
         1 | Europe
         2 | Americas
  (4 rows)

  The above command queries the HR.areaS table.

  NOTICE: The value of the variable is copied literally, so it can even contain unbalanced quotation marks or backslash commands. Therefore, the input content must be meaningful.

• Prompt

  The gsql prompt can be set using the three variables in Table 3. These variables consist of characters and special escape characters.

  Table 3 Prompt variables

  Variable	Description	Example
  PROMPT1	Specifies the normal prompt used when gsql requests a new command. The default value of PROMPT1 is: %/%R%#	PROMPT1 can be used to change the prompt. - Change the prompt to [local]: mogdb=> \set PROMPT1 %M [local:/tmp/gaussdba_mppdb] - Change the prompt to name: mogdb=> \set PROMPT1 name name - Change the prompt to =: mogdb=> \set PROMPT1 %R =
  PROMPT2	Specifies the prompt displayed when more input is expected because the command that is not terminated with a semicolon (;) or a quote (") is not closed.	PROMPT2 can be used to display the prompt. mogdb=# \set PROMPT2 TEST mogdb=# select * from HR.areaS TEST; `area_id
  PROMPT3	Specifies the prompt displayed when the COPY statement (such as COPY FROM STDIN) is run and data input is expected.	PROMPT3 can be used to display the COPY prompt. mogdb=# \set PROMPT3 '>>>>' mogdb=# copy HR.areaS from STDIN; Enter data to be copied followed by a newline. End with a backslash and a period on a line by itself. >>>>1 aa >>>>2 bb >>>>.

  The value of the selected prompt variable is printed literally. However, a value containing a percent sign (%) is replaced by the predefined contents depending on the character following the percent sign (%). For details about the defined substitutions, see Table 4.

  Table 4 Defined substitutions

  Symbol	Description
  %M	Specifies the full host name (with domain name). The full name is [local] if the connection is over a Unix domain socket, or [local:/dir/name] if the Unix domain socket is not at the compiled default location.
  %m	Specifies the host name truncated at the first dot. It is [local] if the connection is over a Unix domain socket.
  %>	Specifies the number of the port that the host is listening on.
  %n	Replaced with the database session username.
  %/	Replaced with the name of the current database.
  %~	Similar to %/. However, the output is tilde (~) if the database is your default database.
  %#	Uses # if the session user is the database administrator. Otherwise, uses >.
  %R	- In PROMPT1 normally =, but ^ if in single-line mode, or ! if the session is disconnected from the database (which can happen if \connect fails). - In PROMPT2 %R is replaced with a hyphen (-), an asterisk (*), a single or double quotation mark, or a dollar sign ($), depending on whether gsql expects more input because the query is inside a /…/ comment or inside a quoted or dollar-escaped string.*
  %x	Replaced with the transaction status. - An empty string when it is not in a transaction block - An asterisk () when it is in a transaction block - An exclamation mark (!) when it is in a failed transaction block - A question mark (?) when the transaction status is indefinite (for example, because there is no connection).
  %digits	Replaced with the character with the specified byte.
  %:name	Specifies the value of the name variable of gsql.
  %command	Specifies command output, similar to substitution with the "^" symbol.
  %[ … %]	Prompts may contain terminal control characters which, for example, change the color, background, or style of the prompt text, or change the title of the terminal window. For example: mogdb=> \set PROMPT1 '%[%033[1;33;40m%]%n@%/%R%[%033[0m%]%#' The output is a boldfaced (1;) yellow-on-black (33;40) prompt on VT100-compatible, color-capable terminals.

  Environment Variables

  Table 5 Environment variables related to gsql

  Name	Description
  COLUMNS	If \set columns is set to 0, this parameter controls the width of the wrapped format. This width determines whether to change the wide output mode into the vertical output mode if automatic expansion is enabled.
  PAGER	If the query results do not fit on the screen, they are redirected through this command. You can use the \pset command to disable the pager. Typically, the more or less command is used for viewing the query result page by page. The default is platform-dependent. NOTE: Display of the less command is affected by the LC_CTYPE environment variable.
  PSQL_EDITOR	The \e and \ef commands use the editor specified by the environment variables. The variables are examined in the order listed. The default editor on Unix is vi.
  EDITOR
  VISUAL
  PSQL_EDITOR_LINENUMBER_ARG	When the \e or \ef command is used with a line number parameter, this variable specifies the command-line parameter used to pass the starting line number to the editor. For editors, such as Emacs or vi, this is a plus sign. Include a space in the value of the variable if space is needed between the option name and the line number. For example: PSQL_EDITOR_LINENUMBER_ARG = '+' PSQL_EDITOR_LINENUMBER_ARG='-line ' A plus sign (+) is used by default on Unix.
  PSQLRC	Specifies the location of the user's .gsqlrc file.
  SHELL	Has the same effect as the ! command.
  TMPDIR	Specifies the directory for storing temporary files. The default value is /tmp.

Usage Guidelines

Prerequisites

The user has the permission to access the database.

Background

Use the gsql command to connect to the remote database service. When connecting to the remote database service, enable remote connection on the server. For details, see "Database Usage > Connecting to a Database > Using gsql to Connect to a Database > Remotely Connecting to a Database" in the Developer Guide.

Procedure

1. Connect to the MogDB server using the gsql tool.

   The gsql tool uses the -d parameter to specify the target database name, the -U parameter to specify the database username, the -h parameter to specify the host name, and the -p parameter to specify the port number.

   NOTE: If the database name is not specified, the default database name generated during initialization will be used. If the database username is not specified, the current OS username will be used by default. If a variable does not belong to any parameter (such as -d and -U), and -d is not specified, the variable will be used as the database name. If -d is specified but -U is not specified, the variable will be used as the database username.

   Example 1: Connect to port 15400 of the mogdb database on the local PC as user omm:

   gsql -d mogdb -p 15400

   Example 2: Connect to the port 15400 of the remote mogdb database as user jack.

   gsql -h 10.180.123.163 -d mogdb -U jack -p 15400

   Example 3: mogdb and omm do not belong to any parameter, and they are used as the database name and the username, respectively.

   gsql mogdb omm -p 15400

   Equals

   gsql -d mogdb -U omm -p 15400

   For details about the gsql parameters, see Command Reference.

2. Run a SQL statement.

   The following takes creating database human_staff as an example:

   CREATE DATABASE human_staff;

Ordinarily, input lines end when a command-terminating semicolon is reached. If the command is sent and executed without any error, the command output is displayed on the screen.

1. Execute gsql meta-commands.

   The following takes the listing of all MogDB databases and description information as an example.

   mogdb=#  \l
                                   List of databases
         Name      |  Owner   | Encoding  | Collate | Ctype |   Access privileges
   ----------------+----------+-----------+---------+-------+-----------------------
    human_resource | omm | SQL_ASCII | C       | C     |
    mogdb       | omm | SQL_ASCII | C       | C     |
    template0      | omm | SQL_ASCII | C       | C     | =c/omm         +
                   |          |           |         |       | omm=CTc/omm
    template1      | omm | SQL_ASCII | C       | C     | =c/omm          +
                   |          |           |         |       | omm=CTc/omm
    human_staff    | omm | SQL_ASCII | C       | C     |
   (5 rows)

   For details about gsql meta-commands, see Meta-Command Reference .

Example

Run the following command to create a tablespace EXAMPLE:

mogdb=# CREATE TABLESPACE EXAMPLE RELATIVE LOCATION 'tablespace1/tablespace_1';
CREATE TABLESPACE

After the tablespace is created, run the following command to create a schema HR:

mogdb=# CREATE schema HR;
CREATE SCHEMA

The example shows how to spread a command over several lines of input. Note the prompt change:

mogdb=# CREATE TABLE HR.areaS(
mogdb(# area_ID   NUMBER,
mogdb(# area_NAME VARCHAR2(25)
mogdb(# )tablespace EXAMPLE;
CREATE TABLE

Query the table definition:

mogdb=# \d HR.areaS
               Table "hr.areas"
  Column   |         Type          | Modifiers
-----------+-----------------------+-----------
 area_id   | numeric               |
 area_name | character varying(25) |
Tablespace: "example"

Insert four lines of data into HR.areaS.

mogdb=# INSERT INTO HR.areaS (area_ID, area_NAME) VALUES (1, 'Europe');
INSERT 0 1
mogdb=# INSERT INTO HR.areaS (area_ID, area_NAME) VALUES (2, 'Americas');
INSERT 0 1
mogdb=# INSERT INTO HR.areaS (area_ID, area_NAME) VALUES (3, 'Asia');
INSERT 0 1
mogdb=# INSERT INTO HR.areaS (area_ID, area_NAME) VALUES (4, 'Middle East and Africa');
INSERT 0 1

Change the prompt.

mogdb=# \set PROMPT1 '%n@%m %~%R%#'
omm@[local] mogdb=#

Query the table:

omm@[local] mogdb=#SELECT * FROM HR.areaS;
 area_id |       area_name
---------+------------------------
       1 | Europe
       4 | Middle East and Africa
       2 | Americas
       3 | Asia
(4 rows)

Use the \pset command to display the table in different ways:

omm@[local] mogdb=#\pset border 2
Border style is 2.
omm@[local] mogdb=#SELECT * FROM HR.areaS;
+---------+------------------------+
| area_id |       area_name        |
+---------+------------------------+
|       1 | Europe                 |
|       2 | Americas               |
|       3 | Asia                   |
|       4 | Middle East and Africa |
+---------+------------------------+
(4 rows)
omm@[local] mogdb=#\pset border 0
Border style is 0.
omm@[local] mogdb=#SELECT * FROM HR.areaS;
area_id       area_name
------- ----------------------
      1 Europe
      2 Americas
      3 Asia
      4 Middle East and Africa
(4 rows)

Use the meta-command:

omm@[local] mogdb=#\a \t \x
Output format is unaligned.
Showing only tuples.
Expanded display is on.
omm@[local] mogdb=#SELECT * FROM HR.areaS;
area_id|2
area_name|Americas

area_id|1
area_name|Europe

area_id|4
area_name|Middle East and Africa

area_id|3
area_name|Asia
omm@[local] mogdb=#

Obtaining Help Information

Procedure

• After connecting to the database, run the following command to obtain the help information:

  gsql --help

  The following help information is displayed:

  ......
  Usage:
    gsql [OPTION]... [DBNAME [USERNAME]]
  
  General options:
    -c, --command=COMMAND    run only single command (SQL or internal) and exit
    -d, --dbname=DBNAME      database name to connect to (default: "omm")
    -f, --file=FILENAME      execute commands from file, then exit
  ......

• After connecting to the database, run the following command to obtain the help information:

  help

  The following help information is displayed:

  You are using gsql, the command-line interface to gaussdb.
  Type:  \copyright for distribution terms
         \h for help with SQL commands
         \? for help with gsql commands
         \g or terminate with semicolon to execute query
         \q to quit

Examples

1. Run the following command to connect to the database:

   gsql -d mogdb -p 15400

   mogdb is the name of the database to be connected, and 15400 is the port number of the primary database node.

   If information similar to the following is displayed, the connection succeeds:

   gsql ((MogDB x.x.x build 56189e20) compiled at 2022-01-07 18:47:53 commit 0 last mr  )
   Non-SSL connection (SSL connection is recommended when requiring high-security)
   Type "help" for help.
   
   mogdb=#

2. View the gsql help information. For details, see Table gsql online help.

   Table 6 gsql online help

   Description	Example
   Query the copyright.	\copyright
   View SQL statements supported by MogDB.	View SQL statements supported by MogDB. To query all SQL statements supported by MogDB, run the following command: mogdb=# \h Available help: ABORT ALTER APP WORKLOAD GROUP … … For example, view parameters of the CREATE DATABASE command: mogdb=# \help CREATE DATABASE Command: CREATE DATABASE Description: create a new database Syntax: CREATE DATABASE database_name `[ [ WITH ] {[ OWNER [=] user_name ]
   View the help information about gsql commands.	For example, view commands supported by gsql. mogdb=# \? General \copyright show FusionInsight LibrA usage and distribution terms `\g [FILE] or ; execute query (and send results to file or

Command Reference

For details about gsql parameters, see Table Common parameters, Table Input and output parameters, Table Output format parameters, and Table Connection parameters.

Table 7 Common parameters

Table 8 Input and output parameters

Table 9 Output format parameters

Table 10 Connection parameters

Meta-Command Reference

This section describes meta-commands provided by gsql after the MogDB database CLI tool is used to connect to a database. A gsql meta-command can be anything that you enter in gsql and begins with an unquoted backslash.

Precautions

• The format of the gsql meta-command is a backslash () followed by a command verb, and then a parameter. The parameters are separated from the command verb and from each other by any number of whitespace characters.
• To include whitespace in a parameter, you can quote it with single quotation marks ("). To include single quotation marks in a parameter, add a backslash in front of it. Anything contained in single quotation marks is furthermore subject to C-like substitutions for \n (new line), \t (tab), \b (backspace), \r (carriage return), \f (form feed), \digits (octal), and \xdigits (hexadecimal).
• Within a parameter, text enclosed in double quotation marks ("") is taken as a command line input to the shell. The command output (with any trailing newline removed) is taken as a parameter.
• If an unquoted parameter begins with a colon (:), the parameter is taken as a gsql variable and the value of the variable is used as the parameter value instead.
• Some commands take an SQL identifier (such as a table name) as a parameter. These parameters follow the SQL syntax rules: Unquoted letters are forced to lowercase, while double quotation marks ("") protect letters from case conversion and allow incorporation of whitespace into the identifier. Within double quotation marks, paired double quotation marks reduce to a single double quotation mark in the result name. For example, FOO"BAR"BAZ is interpreted as fooBARbaz, and "Aweird""name" becomes A weird"name.
• Parameter parsing stops when another unquoted backslash appears. An unquoted backslash is taken as the beginning of a new meta-command. The special sequence \ (two backslashes) marks the end of parameters and continues parsing SQL statements if any. In this way, SQL statements and gsql commands can be freely mixed in a line. However, the parameters of a meta-command cannot continue beyond the end of a line in any situations.

Meta-Commands

For details about meta-commands, see Table Common meta-commands, Table Query buffer meta-commands, Table Input and output meta-commands, Table Information display meta-commands, Table Formatting meta-commands,Table Connection meta-commands , Table OS meta-commands, Table Variable meta-commands, and Table Large object meta-commands.

NOTICE: FILE mentioned in the following commands indicates a file path. This path can be an absolute path such as /home/gauss/file.txt or a relative path, such as file.txt. By default, a file.txt is created in the path where the user runs gsql commands.

Table 11 Common meta-commands

Table 12 Query buffer meta-commands

Table 13 Input and output meta-commands

NOTE: In Table 14, option S indicates displaying the system object and PATTERN indicates displaying the additional description information and the name of the object to be displayed.

Table 14 Information display meta-commands

Table 15 Description of permissions

Table 16 Formatting meta-commands

Table 17 Adjustable printing options

Table 18 Connection meta-commands

Table 19 OS meta-commands

Table 20 Variable meta-commands

Table 21 Common \set commands

Table 22 Large object meta-commands

PATTERN

The various \d commands accept a PATTERN parameter to specify the object name to be displayed. In the simplest case, a pattern is just the exact name of the object. The characters within a pattern are normally folded to lower case, similar to those in SQL names. For example, \dt FOO will display the table named foo. As in SQL names, placing double quotation marks (") around a pattern prevents them being folded to lower case. If you need to include a double quotation mark (") in a pattern, write it as a pair of double quotation marks ("") within a double-quote sequence, which is in accordance with the rules for SQL quoted identifiers. For example, \dt "FOO""BAR" will be displayed as a table named FOO"BAR instead of foo"bar. You cannot put double quotation marks around just part of a pattern, which is different from the normal rules for SQL names. For example, \dt FOO"FOO"BAR will be displayed as a table named fooFOObar if just part of a pattern is quoted.

Whenever the PATTERN parameter is omitted completely, the \d commands display all objects that are visible in the current schema search path, which is equivalent to using an asterisk (*) as the pattern. An object is regarded to be visible if it can be referenced by name without explicit schema qualification. To see all objects in the database regardless of their visibility, use a dot within double asterisks (.) as the pattern.

Within a pattern, the asterisk (*) matches any sequence of characters (including no characters) and a question mark (?) matches any single character. This notation is comparable to Unix shell file name patterns. For example, \\dt displays tables whose names begin with int. But within double quotation marks, the asterisk (*) and the question mark (?) lose these special meanings and are just matched literally.

A pattern that contains a dot (.)s interpreted as a schema name pattern followed by an object name pattern. For example, \dt foo.bar displays all tables (whose names include bar) in schemas starting with foo. If no dot appears, then the pattern matches only visible objects in the current schema search path. Again, a dot within double quotation marks loses its special meaning and is matched literally.

Advanced users can use regular-expression notations, such as character classes. For example [0-9] can be used to match any digit. All regular expression special characters, except the following, work as specified in POSIX regular expressions:

• A dot (.) is used as a separator.
• An asterisk (*) is translated into an asterisk prefixed with a dot (.*), which is a regular-expression marking.
• A question mark (?) is translated into a dot (.).
• A dollar sign ($) is matched literally.

You can, as required, write ?, (R+|), (R|), and R to the following PATTERN characters: ., R*, and R?. The dollar sign ($) does not need to work as a regular-expression character since the pattern must match the whole name, which is different from the usual interpretation of regular expressions. In other words, the dollar sign ($) is automatically appended to your pattern. If you do not expect a pattern to be anchored, write an asterisk (*) at its beginning or end. All regular-expression special characters within double quotation marks lose their special meanings and are matched literally. Regular-expression special characters in operator name patterns (such as the \do parameter) are also matched literally.

FAQs

Low Connection Performance

• log_hostname is enabled, but DNS is incorrect.

  Connect to the database, and run show log_hostname to check whether log_hostname is enabled in the database.

  If it is enabled, the database kernel will use DNS to check the name of the host where the client is deployed. If the primary database node is configured with an incorrect or unreachable DNS server, the database connection will take a long time to set up. For details about this parameter, see the description of log_hostname in section "GUC Parameter Description > Error Reports and Logs > Log Content" in the Developer Guide.

• The database kernel slowly runs the initialization statement.

  Problems are difficult to locate in this scenario. Try using the strace Linux trace command.

  strace gsql -U MyUserName -W MyPassWord -d mogdb -h 127.0.0.1 -p 23508 -r -c '\q'

  The database connection process will be printed on the screen. If the following statement takes a long time to run:

  sendto(3, "Q\0\0\0\25SELECT VERSION()\0", 22, MSG_NOSIGNAL, NULL, 0) = 22
  poll([{fd=3, events=POLLIN|POLLERR}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])

  It indicates that the SELECT VERSION() statement was run slowly.

  After the database is connected, you can run the explain performance select version() statement to find the reason why the initialization statement was run slowly. For more information, see "Performance Tuning > SQL Tuning Guide > SQL Execution Plan" in the Developer Guide.

  An uncommon scenario is that the disk of the machine where the primary database node resides is full or faulty, affecting queries and leading to user authentication failures. As a result, the connection process is suspended. To solve this problem, simply clear the data disk space of the primary database node.

• TCP connection is set up slowly.

  Adapt the steps of troubleshooting slow initialization statement execution. Use strace. If the following statement is run slowly:

  connect(3, {sa_family=AF_FILE, path="/home/test/tmp/gaussdb_llt1/.s.PGSQL.61052"}, 110) = 0

  Or,

  connect(3, {sa_family=AF_INET, sin_port=htons(61052), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EINPROGRESS (Operation now in progress)

  It indicates that the physical connection between the client and the database is set up slowly. In this case, check whether the network is unstable or has high throughput.

Problems in Setting Up Connections

• gsql: could not connect to server: No route to host

  This problem occurs generally because an unreachable IP address or port number was specified. Check whether the values of -h and -p parameters are correct.

• gsql: FATAL: Invalid username/password,login denied.

  This problem occurs generally because an incorrect username or password was entered. Contact the database administrator to check whether the username and password are correct.

• gsql: FATAL: Forbid remote connection with trust method!

  For security purposes, remote login in trust mode is forbidden. In this case, you need to modify the connection authentication information in the pg_hba.conf file. For details, see "Database Security Management > Client Access Authentication > Configuration File Reference" in the Developer Guide.

  NOTE: Do not modify the configurations of the MogDB host in the pg_hba. conf file. Otherwise, the database may become faulty. It is recommended that service applications be deployed outside the MogDB.

• If -h 127.0.0.1 is specified, the database connection is successful. If -h 127.0.0.1 is removed, the connection fails.

  Run the show unix_socket_directory SQL statement to check whether the Unix socket directory used by the primary database node is the same as that specified by $PGHOST in the shell directory.

  If they are different, set $PGHOST to the directory specified by unix_socket_directory.

  For more information about unix_socket_directory, see "GUC Parameter Description > Connection and Authentication > Connection Settings" in the Developer Guide.

• The "libpq.so" loaded mismatch the version of gsql, please check it.

  This problem occurs because the version of libpq.so used in the environment does not match that of gsql. Run the ldd gsql command to check the version of the loaded libpq.so, and then load correct libpq.so by modifying the environment variable LD_LIBRARY_PATH.

• gsql: symbol lookup error: xxx/gsql: undefined symbol: libpqVersionString

  This problem occurs because the version of libpq.so used in the environment does not match that of gsql (or the PostgreSQL libpq.so exists in the environment). Run the ldd gsql command to check the version of the loaded libpq.so, and then load correct libpq.so by modifying the environment variable LD_LIBRARY_PATH.

• gsql: connect to server failed: Connection timed out

  Is the server running on host "xx.xxx.xxx.xxx" and accepting TCP/IP connections on port xxxx?

  This problem is caused by network connection faults. Check the network connection between the client and the database server. If you cannot ping from the client to the database server, the network connection is abnormal. Contact network management personnel for troubleshooting.

  ping -c 4 10.10.10.1
  PING 10.10.10.1 (10.10.10.1) 56(84) bytes of data.
  From 10.10.10.1: icmp_seq=2 Destination Host Unreachable
  From 10.10.10.1 icmp_seq=2 Destination Host Unreachable
  From 10.10.10.1 icmp_seq=3 Destination Host Unreachable
  From 10.10.10.1 icmp_seq=4 Destination Host Unreachable
  --- 10.10.10.1 ping statistics ---
  4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 2999ms

• gsql: FATAL: permission denied for database "mogdb"

  DETAIL: User does not have CONNECT privilege.

  This problem occurs because the user does not have the permission to access the database. To solve this problem, perform the following steps:

  1. Connect to the database as the system administrator dbadmin.

     gsql -d mogdb -U dbadmin -p 15400

  2. Grant the user with the permission to access the database.

     GRANT CONNECT ON DATABASE mogdb TO user1;

  NOTE: Actually, some common misoperations may also cause a database connection failure, for example, entering an incorrect database name, username, or password. Misoperations are accompanied with an error information on the client tool.

  gsql -d mogdb -p 15400
  gsql: FATAL:  database "mogdb" does not exist
  gsql -d mogdb -U user1 -W Enmo@789 -p 15400
  gsql: FATAL:  Invalid username/password,login denied.

• gsql: FATAL: sorry, too many clients already, active/non-active: 2/10/3.

  This problem occurs because the number of system connections exceeds the upper limit. Contact the database administrator to release unnecessary sessions.

  For details about how to view the number of user session connections.

  You can view the session status in the PG_STAT_ACTIVITY view. To release unnecessary sessions, use the pg_terminate_backend function.

  select datid,pid,state from pg_stat_activity;
   datid |       pid       | state
  -------+-----------------+--------
  13205 | 139834762094352 | active
  13205 | 139834759993104 | idle
  (2 rows)

  The value of pid is the thread ID of the session. Terminate the session using its thread ID.

  SELECT PG_TERMINATE_BACKEND(139834759993104);
  PG_TERMINATE_BACKEND
  ----------------------
   t
  (1 row)

  • View the maximum number of sessions connected to a specific user

    Run the following command to view the upper limit of the number of USER1's session connections. -1 indicates that no upper limit is set for the number of user1's session connections

    SELECT ROLNAME,ROLCONNLIMIT FROM PG_ROLES WHERE ROLNAME='user1';
    rolname | rolconnlimit
    --------+-----
    user1    |           -1
    (1 row)
    ``

  • View the maximum number of sessions connected to a specific database

    Run the following command to view the upper limit of the number of mogdb's session connections. -1 indicates that no upper limit is set for the number of mogdb's session connections

    SELECT DATNAME,DATCONNLIMIT FROM PG_DATABASE WHERE DATNAME='mogdb';
    datname  | datconnlimit
    ------+-----
    mogdb |           -1 (1 row)
    (1 row)

  • View the number of session connections that have been used by a specific database

    Run the following command to view the number of session connections that have been used by mogdb. 1 indicates the number of session connections that have been used by mogdb.

    SELECT COUNT(*) FROM PG_STAT_ACTIVITY WHERE DATNAME='mogdb';
    count
    ------
    1
    (1 row)

• gsql: wait xxx.xxx.xxx.xxx:xxxx timeout expired

  When gsql initiates a connection request to the database, a 5-minute timeout period is used. If the database cannot correctly authenticate the client request and client identity within this period, gsql will exit the connection process for the current session, and will report the above error.

  Generally, this problem is caused by the incorrect host and port (that is, the xxx part in the error information) specified by the -h and -p parameters. As a result, the communication fails. Occasionally, this problem is caused by network faults. To resolve this problem, check whether the host name and port number of the database are correct.

• gsql: could not receive data from server: Connection reset by peer.

  Check whether primary database node logs contain information similar to "FATAL: cipher file "/data/dbnode/server.key.cipher" has group or world access". This error is usually caused by tampering with the permissions for data directories or some key files by mistake. For details about how to correct the permissions, see related permissions for files on other normal instances.

• gsql: FATAL: GSS authentication method is not allowed because XXXX user password is not disabled.

  In pg_hba.conf of the target primary database node, the authentication mode is set to gss for authenticating the IP address of the current client. However, this authentication algorithm cannot authenticate clients. Change the authentication algorithm to sha256 and try again. For details, see "Database Security Management > Client Access Authentication > Configuration File Reference" in the Developer Guide.

  NOTE:

  • Do not modify the configurations of the MogDB host in the pg_hba. conf file. Otherwise, the database may become faulty.
  • It is recommended that service applications be deployed outside the MogDB.

Other Faults

• There is a core dump or abnormal exit due to the bus error.

  Generally, this problem is caused by changes in loading the shared dynamic library (.so file in Linux) during process running. Alternatively, if the process binary file changes, the execution code for the OS to load machines or the entry for loading a dependent library will change accordingly. In this case, the OS kills the process for protection purposes, generating a core dump file.

  To resolve this problem, try again. In addition, do not run service programs in MogDB during O&M operations, such as an upgrade, preventing such a problem caused by file replacement during the upgrade.

  NOTE: A possible stack of the core dump file contains dl_main and its function calling. The file is used by the OS to initialize a process and load the shared dynamic library. If the process has been initialized but the shared dynamic library has not been loaded, the process cannot be considered completely started.