PostgreSQL 9.5alpha1 Documentation | |||
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The catalog pg_tablesample_method stores information about table sampling methods which can be used in TABLESAMPLE clause of a SELECT statement.
Table 49-48. pg_tablesample_method Columns
Name | Type | References | Description |
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oid | oid | Row identifier (hidden attribute; must be explicitly selected) | |
tsmname | name | Name of the sampling method | |
tsmseqscan | bool | If true, the sampling method scans the whole table sequentially. | |
tsmpagemode | bool | If true, the sampling method always reads the pages completely. | |
tsminit | regproc | pg_proc.oid | "Initialize the sampling scan" function |
tsmnextblock | regproc | pg_proc.oid | "Get next block number" function |
tsmnexttuple | regproc | pg_proc.oid | "Get next tuple offset" function |
tsmexaminetuple | regproc | pg_proc.oid | Function which examines the tuple contents and decides if to return it, or zero if none |
tsmend | regproc | pg_proc.oid | "End the sampling scan" function |
tsmreset | regproc | pg_proc.oid | "Restart the state of sampling scan" function |
tsmcost | regproc | pg_proc.oid | Costing function |