Database Object Functions

Database Object Size Functions

Database object size functions calculate the actual disk space used by database objects.

• pg_column_size(any)

  Description: Specifies the number of bytes used to store a particular value (possibly compressed)

  Return type: int

  Note:pg_column_size displays the space for storing an independent data value.

  mogdb=# SELECT pg_column_size(1);
   pg_column_size
  ----------------
                4
  (1 row)

• pg_database_size(oid)

  Description: Specifies the disk space used by the database with the specified OID.

  Return type: bigint

• pg_database_size(name)

  Description: Specifies the disk space used by the database with the specified name.

  Return type: bigint

  Note:pg_database_size receives the OID or name of a database and returns the disk space used by the corresponding object.

  Example:

  mogdb=# SELECT pg_database_size('mogdb');
   pg_database_size
  ------------------
           51590112
  (1 row)

• pg_relation_size(oid)

  Description: Specifies the disk space used by the table with a specified OID or index.

  Return type: bigint

• get_db_source_datasize()

  Description: Estimates the total size of non-compressed data in the current database.

  Return type: bigint

  Note: (1) ANALYZE must be performed before this function is called. (2) Calculate the total size of non-compressed data by estimating the compression rate of column-store tables.

  Example:

  mogdb=# analyze;
  ANALYZE
  mogdb=# select get_db_source_datasize();
   get_db_source_datasize
  ------------------------
              35384925667
  (1 row)

• pg_relation_size(text)

  Description: Specifies the disk space used by the table with a specified name or index. The table name can be schema-qualified.

  Return type: bigint

• pg_relation_size(relation regclass, fork text)

  Description: Specifies the disk space used by the specified bifurcating tree ('main', 'fsm', or 'vm') of a certain table or index.

  Return type: bigint

• pg_relation_size(relation regclass)

  Description: Is an abbreviation of pg_relation_size(…, 'main').

  Return type: bigint

  Note:pg_relation_size receives the OID or name of a table, index, or compressed table, and returns the size.

• pg_partition_size(oid,oid)

  Description: Specifies the disk space used by the partition with a specified OID. The first oid is the OID of the table and the second oid is the OID of the partition.

  Return type: bigint

• pg_partition_size(text, text)

  Description: Specifies the disk space used by the partition with a specified name. The first text is the table name and the second text is the partition name.

  Return type: bigint

• pg_partition_indexes_size(oid,oid)

  Description: Specifies the disk space used by the index of the partition with a specified OID. The first oid is the OID of the table and the second oid is the OID of the partition.

  Return type: bigint

• pg_partition_indexes_size(text,text)

  Description: Specifies the disk space used by the index of the partition with a specified name. The first text is the table name and the second text is the partition name.

  Return type: bigint

• pg_indexes_size(regclass)

  Description: Specifies the total disk space used by the index appended to the specified table.

  Return type: bigint

• pg_size_pretty(bigint)

  Description: Converts a size in bytes expressed as a 64-bit integer into a human-readable format with size units.

  Return type: text

• pg_size_pretty(numeric)

  Description: Converts a size in bytes expressed as a numeric value into a human-readable format with size units.

  Return type: text

  Note:pg_size_pretty formats the results of other functions into a human-readable format. KB/MB/GB/TB can be used.

• pg_table_size(regclass)

  Description: Specifies the disk space used by the specified table, excluding indexes (but including TOAST, free space mapping, and visibility mapping).

  Return type: bigint

• pg_tablespace_size(oid)

  Description: Specifies the disk space used by the tablespace with a specified OID.

  Return type: bigint

• pg_tablespace_size(name)

  Description: Specifies the disk space used by the tablespace with a specified name.

  Return type: bigint

  Note:

  pg_tablespace_size receives the OID or name of a database and returns the disk space used by the corresponding object.

• pg_total_relation_size(oid)

  Description: Specifies the disk space used by the table with a specified OID, including the index and the compressed data.

  Return type: bigint

• pg_total_relation_size(regclass)

  Description: Specifies the total disk space used by the specified table, including all indexes and TOAST data.

  Return type: bigint

• pg_total_relation_size(text)

  Description: Specifies the disk space used by the table with a specified name, including the index and the compressed data. The table name can be schema-qualified.

  Return type: bigint

  Note:pg_total_relation_size receives the OID or name of a table or a compressed table, and returns the sizes of the data, related indexes, and the compressed table in bytes.

• datalength(any)

  Description: Specifies the number of bytes used by an expression of a specified data type (data management space, data compression, or data type conversion is not considered).

  Return type: int

  Note:datalength is used to calculate the space of an independent data value.

  Example:

  mogdb=# SELECT datalength(1);
  datalength
  ------------
  4
  (1 row)

  The following table lists the supported data types and calculation methods.

  Data Type	Storage Space
  Numeric data types	Integer types	TINYINT	1
  SMALLINT	2
  INTEGER	4
  BINARY_INTEGER	4
  BIGINT	8
  Any-precision types	DECIMAL	Every four decimal digits occupy two bytes. The digits before and after the decimal point are calculated separately.
  NUMERIC	Every four decimal digits occupy two bytes. The digits before and after the decimal point are calculated separately.
  NUMBER	Every four decimal digits occupy two bytes. The digits before and after the decimal point are calculated separately.
  Sequence integer	SMALLSERIAL	2
  SERIAL	4
  BIGSERIAL	8
  Floating point types	FLOAT4	4
  DOUBLE PRECISION	8
  FLOAT8	8
  BINARY_DOUBLE	8
  FLOAT[(p)]	Every four decimal digits occupy two bytes. The digits before and after the decimal point are calculated separately.
  DEC[(p[,s])]	Every four decimal digits occupy two bytes. The digits before and after the decimal point are calculated separately.
  INTEGER[(p[,s])]	Every four decimal digits occupy two bytes. The digits before and after the decimal point are calculated separately.
  Boolean data types	Boolean type	BOOLEAN	1
  Character data types	Character types	CHAR	n
  CHAR(n)	n
  CHARACTER(n)	n
  NCHAR(n)	n
  VARCHAR(n)	n
  CHARACTER	Actual number of bytes of a character
  VARYING(n)	Actual number of bytes of a character
  VARCHAR2(n)	Actual number of bytes of a character
  NVARCHAR2(n)	Actual number of bytes of a character
  TEXT	Actual number of bytes of a character
  CLOB	Actual number of bytes of a character
  Time data types	Time types	DATE	8
  TIME	8
  TIMEZ	12
  TIMESTAMP	8
  TIMESTAMPZ	8
  SMALLDATETIME	8
  INTERVAL DAY TO SECOND	16
  INTERVAL	16
  RELTIME	4
  ABSTIME	4
  TINTERVAL	12

Database Object Position Functions

• pg_relation_filenode(relation regclass)

  Description: Specifies the ID of a filenode with the specified relationship.

  Return type: oid

  Description:pg_relation_filenode receives the OID or name of a table, index, sequence, or compressed table, and returns the filenode number allocated to it. The filenode is the basic component of the file name used by the relationship. For most tables, the result is the same as that of pg_class.relfilenode. For the specified system directory, relfilenode is 0 and this function must be used to obtain the correct value. If a relationship that is not stored is transmitted, such as a view, this function returns NULL.

• pg_relation_filepath(relation regclass)

  Description: Specifies the name of a file path with the specified relationship.

  Return type: text

  Description:pg_relation_filepath is similar to pg_relation_filenode, except that pg_relation_filepath returns the whole file path name for the relationship (relative to the data directory PGDATA of MogDB).

• pg_filenode_relation(tablespace oid, filenode oid)

  Description: Obtains the table names corresponding to the tablespace and relfilenode.

  Return type: regclass

• pg_partition_filenode(partition_oid)

  Description: Obtains the filenode corresponding to the OID lock of a specified partitioned table.

  Return type: oid

• pg_partition_filepath(partition_oid)

  Description: Specifies the file path name of a partition.

  Return type: text