Explain PRAGMA SERIALLY_REUSABLE

Normally package state (spec variables, cursors, the initialization block's effects) lives for the whole session. PRAGMA SERIALLY_REUSABLE, placed in the spec (and body if it has one), makes the package state last only for one server call: it is reinitialised on the next call and the memory returns to the pool. It suits large work areas you do not want to hold per session, but breaks any design that deliberately caches across calls, and it cannot be used from a single SQL statement's context.

CREATE OR REPLACE PACKAGE scratch_pkg IS
  PRAGMA SERIALLY_REUSABLE;
  g_buffer  DBMS_SQL.VARCHAR2A;      -- large, rebuilt every call
  PROCEDURE load;
END scratch_pkg;
/
CREATE OR REPLACE PACKAGE BODY scratch_pkg IS
  PRAGMA SERIALLY_REUSABLE;
  PROCEDURE load IS
  BEGIN
    g_buffer.DELETE;                 -- always starts empty each server call
    -- ... fill g_buffer ...
  END;
END scratch_pkg;
/