Help Center> GaussDB(DWS)> Best Practices> Database Management> Viewing Table and Database Information
Updated on 2024-06-07 GMT+08:00

Viewing Table and Database Information

Querying Table Information

  • Querying information about all tables in a database using the pg_tables system catalog
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    SELECT * FROM pg_tables;
    
  • Querying the table structure using \d+ command of the gsql tool.
    Example: Create a table customer_t1 and insert data into the table.
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    CREATE TABLE customer_t1
    (
        c_customer_sk             integer,
        c_customer_id             char(5),
        c_first_name              char(6),
        c_last_name               char(8)
    )
    with (orientation = column,compression=middle)
    distribute by hash (c_last_name);
    
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    INSERT INTO customer_t1 (c_customer_sk, c_customer_id, c_first_name) VALUES
        (6885, 'map', 'Peter'),
        (4321, 'river', 'Lily'),
        (9527, 'world', 'James');
    

    Query the table structure. If no schema is specified when you create a table, the schema of the table defaults to public.

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    \d+ customer_t1;
                              Table "public.customer_t1"
        Column     |     Type     | Modifiers | Storage  | Stats target | Description
    ---------------+--------------+-----------+----------+--------------+-------------
     c_customer_sk | integer      |           | plain    |              |
     c_customer_id | character(5) |           | extended |              |
     c_first_name  | character(6) |           | extended |              |
     c_last_name   | character(8) |           | extended |              |
    Has OIDs: no
    Distribute By: HASH(c_last_name)
    Location Nodes: ALL DATANODES
    Options: orientation=column, compression=middle, colversion=2.0, enable_delta=false
    

    The options may vary in different versions but the difference does not affect services. The options here are for reference only. The actual options are subject to the version.

  • Use pg_get_tabledef to query the table definition.
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    SELECT * FROM PG_GET_TABLEDEF('customer_t1');
                                      pg_get_tabledef                                  
    -----------------------------------------------------------------------------------
     SET search_path = tpchobs;                                                       +
     CREATE  TABLE customer_t1 (                                                      +
             c_customer_sk integer,                                                   +
             c_customer_id character(5),                                              +
             c_first_name character(6),                                               +
             c_last_name character(8)                                                 +
     )                                                                                +
     WITH (orientation=column, compression=middle, colversion=2.0, enable_delta=false)+
     DISTRIBUTE BY HASH(c_last_name)                                                  +
     TO GROUP group_version1;
    (1 row)
    
  • Querying all data in customer_t1
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    SELECT * FROM customer_t1;
     c_customer_sk | c_customer_id | c_first_name | c_last_name
    ---------------+---------------+--------------+-------------
              6885 | map           | Peter        |
              4321 | river         | Lily         |
              9527 | world         | James        |
    (3 rows)
    
  • Querying all data of a column in customer_t1 using SELECT
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    SELECT c_customer_sk FROM customer_t1;
     c_customer_sk
    ---------------
              6885
              4321
              9527
    (3 rows)
    
  • Check whether a table has been analyzed. The time when the table was analyzed will be returned. If nothing is returned, it indicates that the table has not been analyzed.
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    SELECT pg_stat_get_last_analyze_time(oid),relname FROM pg_class where relkind='r'; 
    

    Query the time when the public table was analyzed.

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    SELECT pg_stat_get_last_analyze_time(c.oid),c.relname FROM pg_class c LEFT JOIN pg_namespace n ON c.relnamespace = n.oid WHERE c.relkind='r' AND n.nspname='public';
     pg_stat_get_last_analyze_time |       relname
    -------------------------------+----------------------
     2022-05-17 07:48:26.923782+00 | warehouse_t19
     2022-05-17 07:48:26.964512+00 | emp
     2022-05-17 07:48:27.016709+00 | test_trigger_src_tbl
     2022-05-17 07:48:27.045385+00 | customer
     2022-05-17 07:48:27.062486+00 | warehouse_t1
     2022-05-17 07:48:27.114884+00 | customer_t1
     2022-05-17 07:48:27.172256+00 | product_info_input
     2022-05-17 07:48:27.197014+00 | tt1
     2022-05-17 07:48:27.212906+00 | timezone_test
    (9 rows)
    
  • Quickly query the column information of a table. If a view in information_schema has a large number of objects in the database, it takes a long time to return the result. You can run the following SQL statement to quickly query the column information of one or more tables:
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    SELECT /*+ nestloop(a c)*/ c.column_name, c.data_type, c.ordinal_position, pgd.description, pp.partkey, c.is_nullable, c.column_default, c.character_maximum_length, c.numeric_precision,  c.numeric_scale, c.datetime_precision, c.interval_type, c.udt_name from information_schema.columns as c left join pg_namespace sp on sp.nspname = c.table_schema left join pg_class cla on cla.relname = c.table_name and cla.relnamespace = sp.oid left join pg_catalog.pg_partition pp on (pp.parentid = cla.oid and pp.parttype = 'r') left join pg_catalog.pg_description pgd on (pgd.objoid=cla.oid and pgd.objsubid = c.ordinal_position)where c.table_name in ('tablename') and c.table_schema = 'public';
    

    For example, to quickly query the column information of the customer_t1 table, run the following command:

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    SELECT /*+ nestloop(a c)*/ c.column_name, c.data_type, c.ordinal_position, pgd.description, pp.partkey, c.is_nullable, c.column_default, c.character_maximum_length, c.numeric_precision, c.numeric_scale, c.datetime_precision, c.interval_type, c.udt_name from information_schema.columns as c left join pg_namespace sp on sp.nspname = c.table_schema left join pg_class cla on cla.relname = c.table_name and cla.relnamespace = sp.oid left join pg_catalog.pg_partition pp on (pp.parentid = cla.oid and pp.parttype = 'r') left join pg_catalog.pg_description pgd on (pgd.objoid=cla.oid and pgd.objsubid = c.ordinal_position) where c.table_name in ('customer_t1') and c.table_schema = 'public';
      column_name  | data_type | ordinal_position | description | partkey | is_nullable | column_default | character_maximum_length | numeric_precision | numeric_scale | datetime_precision | interval_type | udt_name
    ---------------+-----------+------------------+-------------+---------+-------------+----------------+--------------------------+-------------------+-------------
    --+--------------------+---------------+----------
     c_last_name   | character |                4 |             |         | YES         |                |                        8 |                   |
      |                    |               | bpchar
     c_first_name  | character |                3 |             |         | YES         |                |                        6 |                   |
      |                    |               | bpchar
     c_customer_id | character |                2 |             |         | YES         |                |                        5 |                   |
      |                    |               | bpchar
     c_customer_sk | integer   |                1 |             |         | YES         |                |                          |                32 |
    0 |                    |               | int4
    (4 rows)
    
  • Obtain the table definition by querying audit logs.

    Use the pgxc_query_audit function to query audit logs of all CNs. The syntax is as follows:

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    pgxc_query_audit(timestamptz startime,timestamptz endtime)
    

    Query the audit records of multiple objects.

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    SET audit_object_name_format TO 'all';
    SELECT object_name,result,operation_type,command_text FROM pgxc_query_audit('2022-08-26 8:00:00','2022-08-26 22:55:00') where command_text like '%student%';
    

Querying the Table Size

  • Querying the total size of a table (indexes and data included)
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    SELECT pg_size_pretty(pg_total_relation_size('<schemaname>.<tablename>'));
    

    Example:

    First, create an index on customer_t1.

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    CREATE INDEX index1 ON customer_t1 USING btree(c_customer_sk);
    

    Then, query the size of table customer_t1 of public.

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    SELECT pg_size_pretty(pg_total_relation_size('public.customer_t1'));
     pg_size_pretty
    ----------------
     264 kB
    (1 row)
    
  • Querying the size of a table (indexes excluded)
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    SELECT pg_size_pretty(pg_relation_size('<schemaname>.<tablename>'));
    
    Example: Query the size of table customer_t1 of public.
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    SELECT pg_size_pretty(pg_relation_size('public.customer_t1'));
     pg_size_pretty
    ----------------
     208 kB
    (1 row)
    
  • Query all the tables, ranked by their occupied space.
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    SELECT table_schema || '.' || table_name AS table_full_name, pg_size_pretty(pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')) AS size FROM information_schema.tables
    ORDER BY
    pg_total_relation_size('"' || table_schema || '"."' || table_name || '"') DESC limit xx;
    
    Example 1: Query the 15 tables that occupy the most space.
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    SELECT table_schema || '.' || table_name AS table_full_name, pg_size_pretty(pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')) AS size FROM information_schema.tables
    ORDER BY
    pg_total_relation_size('"' || table_schema || '"."' || table_name || '"') DESC limit 15;
          table_full_name      |  size
    ---------------------------+---------
     pg_catalog.pg_attribute   | 2048 KB
     pg_catalog.pg_rewrite     | 1888 KB
     pg_catalog.pg_depend      | 1464 KB
     pg_catalog.pg_proc        | 1464 KB
     pg_catalog.pg_class       | 512 KB
     pg_catalog.pg_description | 504 KB
     pg_catalog.pg_collation   | 360 KB
     pg_catalog.pg_statistic   | 352 KB
     pg_catalog.pg_type        | 344 KB
     pg_catalog.pg_operator    | 224 KB
     pg_catalog.pg_amop        | 208 KB
     public.tt1                | 160 KB
     pg_catalog.pg_amproc      | 120 KB
     pg_catalog.pg_index       | 120 KB
     pg_catalog.pg_constraint  | 112 KB
    (15 rows)
    
    Example 2: Query the top 20 tables with the largest space usage in the public schema.
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    SELECT table_schema || '.' || table_name AS table_full_name, pg_size_pretty(pg_total_relation_size('"' || table_schema || '"."' || table_name || '"')) AS size FROM information_schema.tables where table_schema='public'
    ORDER BY
    pg_total_relation_size('"' || table_schema || '"."' || table_name || '"') DESC limit 20;
           table_full_name       |  size
    -----------------------------+---------
     public.tt1                  | 160 KB
     public.product_info_input   | 112 KB
     public.customer_t1          | 96 KB
     public.warehouse_t19        | 48 KB
     public.emp                  | 32 KB
     public.customer             | 0 bytes
     public.test_trigger_src_tbl | 0 bytes
     public.warehouse_t1         | 0 bytes
    (8 rows)
    

Quickly Querying the Space Occupied by All Tables in the Database

In a large cluster (8.1.3 or later) with a large amount of data (more than 1000 tables), you are advised to use the pgxc_wlm_table_distribution_skewness view to query all tables in the database. This view can be used to query the tablespace usage and data skew in the database. The unit of total_size and avg_size is byte.

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SELECT *, pg_size_pretty(total_size) as tableSize FROM pgxc_wlm_table_distribution_skewness ORDER BY total_size desc;
    schema_name     |                    table_name                     | total_size | avg_size  | max_percent | min_percent | skew_percent | tablesize 
--------------------+---------------------------------------------------+------------+-----------+-------------+-------------+--------------+-----------
 public             | history_tbs_test_row_1                            |  804347904 | 134057984 |       18.02 |       15.63 |         7.53 | 767 MB
 public             | history_tbs_test_row_3                            |  402096128 |  67016021 |       18.30 |       15.60 |         8.90 | 383 MB
 public             | history_tbs_test_row_2                            |  401743872 |  66957312 |       18.01 |       15.01 |         7.47 | 383 MB
 public             | i_history_tbs_test_1                              |  325263360 |  54210560 |       17.90 |       15.50 |         6.90 | 310 MB

The query result shows that the history_tbs_test_row_1 table occupies the largest space and data skew occurs.

  1. The pgxc_wlm_table_distribution_skewness view can be queried only when the GUC parameter use_workload_manager and enable_perm_space is enabled. In earlier versions, you are advised to use the table_distribution() function to query the entire database. If only the size of a table is queried, the table_distribution(schemaname text, tablename text) function is recommended.
  2. In 8.2.1 and later cluster versions, GaussDB(DWS) supports the pgxc_wlm_table_distribution_skewness view, which can be directly used for query.
  3. In the 8.1.3 cluster version, you can use the following definition to create a view and then perform query:
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CREATE OR REPLACE VIEW
pgxc_wlm_table_distribution_skewness AS
WITH skew AS
(
SELECT
schemaname,
tablename,
pg_catalog.sum(dnsize)
AS totalsize,
pg_catalog.avg(dnsize)
AS avgsize,
pg_catalog.max(dnsize)
AS maxsize,
pg_catalog.min(dnsize)
AS minsize,
(maxsize
- avgsize) * 100 AS skewsize
FROM
pg_catalog.gs_table_distribution()
GROUP
BY schemaname, tablename
)
SELECT
    schemaname AS schema_name,
    tablename AS table_name,
    totalsize AS total_size,
    avgsize::numeric(1000) AS avg_size,
    (
        CASE
            WHEN totalsize = 0 THEN 0.00
            ELSE (maxsize * 100 /
totalsize)::numeric(5, 2)
        END
    ) AS max_percent,
    (
        CASE
            WHEN totalsize = 0 THEN 0.00
            ELSE (minsize * 100 /
totalsize)::numeric(5, 2)
        END
    ) AS min_percent,
    (
        CASE
            WHEN totalsize = 0 THEN 0.00
            ELSE (skewsize /
maxsize)::numeric(5, 2)
        END
    ) AS skew_percent
FROM skew;

Querying Database Information

  • Querying the database list using the \l meta-command of the gsql tool.
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    \l
                              List of databases
       Name    | Owner | Encoding  | Collate | Ctype | Access privileges
    -----------+-------+-----------+---------+-------+-------------------
     gaussdb   | Ruby  | SQL_ASCII | C       | C     |
     template0 | Ruby  | SQL_ASCII | C       | C     | =c/Ruby           +
               |       |           |         |       | Ruby=CTc/Ruby
     template1 | Ruby  | SQL_ASCII | C       | C     | =c/Ruby           +
               |       |           |         |       | Ruby=CTc/Ruby
    (3 rows)
    
    • If the parameters LC_COLLATE and LC_CTYPE are not specified during database installation, the default values of them are C.
    • If LC_COLLATE and LC_CTYPE are not specified during database creation, the sorting order and character classification of the template database are used by default.

      For details, see CREATE DATABASE.

  • Querying the database list using the pg_database system catalog
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    SELECT datname FROM pg_database;
      datname
    -----------
     template1
     template0
     gaussdb
    (3 rows)
    

Querying the Database Size

Querying the size of databases
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select datname,pg_size_pretty(pg_database_size(datname)) from pg_database;

Example:

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select datname,pg_size_pretty(pg_database_size(datname)) from pg_database;
  datname  | pg_size_pretty
-----------+----------------
 template1 | 61 MB
 template0 | 61 MB
 postgres  | 320 MB
(3 rows)

Querying the Size of a Table and the Size of the Corresponding Index in a Specified Schema

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SELECT
    t.tablename,
    indexname,
    c.reltuples AS num_rows,
    pg_size_pretty(pg_relation_size(quote_ident(t.tablename)::text)) AS table_size,
    pg_size_pretty(pg_relation_size(quote_ident(indexrelname)::text)) AS index_size,
    CASE WHEN indisunique THEN 'Y'
       ELSE 'N'
    END AS UNIQUE,
    idx_scan AS number_of_scans,
    idx_tup_read AS tuples_read,
    idx_tup_fetch AS tuples_fetched
FROM pg_tables t
LEFT OUTER JOIN pg_class c ON t.tablename=c.relname
LEFT OUTER JOIN
    ( SELECT c.relname AS ctablename, ipg.relname AS indexname, x.indnatts AS number_of_columns, idx_scan, idx_tup_read, idx_tup_fetch, indexrelname, indisunique FROM pg_index x
           JOIN pg_class c ON c.oid = x.indrelid
           JOIN pg_class ipg ON ipg.oid = x.indexrelid
           JOIN pg_stat_all_indexes psai ON x.indexrelid = psai.indexrelid )
    AS foo
    ON t.tablename = foo.ctablename
WHERE t.schemaname='public'
ORDER BY 1,2;