The PER_STMT_PREP memory duration
A PER_STMT_PREP memory pool is associated with each SQL prepared statement. A prepared statement is an SQL statement that is parsed and ready for execution.
| Method | To create a prepared statement | To drop a prepared statement |
|---|---|---|
| Client application (SQL) | PREPARE | FREE |
| C UDR (DataBlade API) | mi_prepare() | mi_drop_prepared_statement() |
When a C UDR allocates PER_STMT_PREP memory, this memory is available to all routine instances that execute before the current prepared statement is dropped. Unlike PER_STMT_EXEC memory, PER_STMT_PREP memory does not get freed upon re-execution of the prepared statement; that is, it remains allocated if the cursor is closed and reopened. For example, in the second code fragment in Examples of using PER_STMT_EXEC memory duration, any PER_STMT_PREP memory that a_func() allocated is not released when the cursor is reopened. Therefore, any code that needs to access this memory once the cursor is reopened can do so. The PER_STMT_PREP memory that a_func() allocates remains allocated until the mi_drop_prepared_statement() drops the stmt prepared statement.
When the prepared SQL statement is dropped, the database server reclaims any PER_STMT_PREP memory in the memory context. It does not reclaim any memory in the memory context with a duration higher than PER_STMT_PREP.
No DataBlade API constructor function allocates its data type structure with a memory duration of PER_STMT_PREP.