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.
1 2 3 4 5 | gaussdb=# 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:
1 2 3 4 5 | gaussdb=# SELECT pg_database_size('testdb'); pg_database_size ------------------ 51590112 (1 row) |
The query time of the pg_database_size(oid/name) function is linearly related to the number of object files in the database corresponding to the OID/name. To evaluate the time required, perform the following steps:
- Since the time required is related to the software and hardware environments, the test result of a certain database (the number of object files in the selected database should not be too large) is used as the benchmark. Calculate the time consumed by a single object file (database_size_t) based on the query time and the number of object files in the database.
- Obtain the OID of the database to be queried using the command SELECT oid, * FROM pg_database WHERE datname = 'database';. In the base and pg_tblspc tablespace directories, count the total number of files (database_obj_num) in the directory corresponding to the OID. If the directory contains subdirectories, you need to enter it to view the number of object files. You can run ls | wc -l to query the number of files in the directory.
- Calculate the estimated total time consumption based on database_size_t (time consumption of a single file) and database_obj_num (number of all object files in the database) in the benchmark test result. The total time consumption is equal to database_size_t multiplied by database_obj_num. If the estimated latency is too long, consider adjusting the execution timeout threshold to avoid unnecessary alarms.
- The preceding steps assess the time needed to obtain the database size on a DN. In a distributed environment, the overall time required depends on the DN with the most object files or the DN with the longest processing time.
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: ANALYZE must be performed before this function is called.
Example:
1 2 3 4 5 6 7 | gaussdb=# analyze; ANALYZE gaussdb=# 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, an index, or a 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, and 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:
gaussdb=# 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 | ||
| Arbitrary 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. | ||
| Serial integers | 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 | ||
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