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Calculating the size of a column type in Postgresql

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sql

postgresql

I am trying to figure out how to determine the size of a specific column in database for instance I have two columns called sourceip, destinationip that are both 16 byte fields.

I thought this would be somewhere in the information_schema or \d+ but I cannot find a specific command to isolate the size of each column type.

Can you calculate column type size in database or do you just have to reference the byte size for each type in the Postgresql documentation?

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user7980 Avatar asked Sep 12 '12 18:09

user7980


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1 Answers

only few types in pg has fixed length - almost all types are varlena type - it has dynamic length. You can check queries like

 postgres=# select typlen from pg_type where oid = 'int'::regtype::oid;
  typlen 
 --------
       4
 (1 row)


 postgres=# select attlen from pg_attribute where attrelid = 'x'::regclass and attname = 'a';
  attlen 
 --------
       4
 (1 row)

When result is not -1, then type has not fixed length

for varlena types use pg_column_size function:

postgres=# \df *size*
                                   List of functions
   Schema   |          Name          | Result data type | Argument data types |  Type  
------------+------------------------+------------------+---------------------+--------
 pg_catalog | pg_column_size         | integer          | "any"               | normal
 pg_catalog | pg_database_size       | bigint           | name                | normal
 pg_catalog | pg_database_size       | bigint           | oid                 | normal
 pg_catalog | pg_indexes_size        | bigint           | regclass            | normal
 pg_catalog | pg_relation_size       | bigint           | regclass            | normal
 pg_catalog | pg_relation_size       | bigint           | regclass, text      | normal
 pg_catalog | pg_size_pretty         | text             | bigint              | normal
 pg_catalog | pg_size_pretty         | text             | numeric             | normal
 pg_catalog | pg_table_size          | bigint           | regclass            | normal
 pg_catalog | pg_tablespace_size     | bigint           | name                | normal
 pg_catalog | pg_tablespace_size     | bigint           | oid                 | normal
 pg_catalog | pg_total_relation_size | bigint           | regclass            | normal
(12 rows)



 postgres=# select pg_column_size('Hello');
  pg_column_size 
 ----------------
          6
 (1 row)

 postgres=# select pg_column_size(10);
  pg_column_size 
 ----------------
               4
 (1 row)

 postgres=# select pg_column_size(now());
  pg_column_size 
 ----------------
               8
like image 164
Pavel Stehule Avatar answered Oct 14 '22 06:10

Pavel Stehule