It is impossible to read the value from the SEARCH_PATH context variable if it exceeds 255 characters.

[AlexBekhtin]

SET SEARCH_PATH TO TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA, TEST_SCHEMA;

SELECT RDB$GET_CONTEXT('SYSTEM', 'SEARCH_PATH') FROM RDB$DATABASE;

Statement failed, SQLSTATE = 22001
arithmetic exception, numeric overflow, or string truncation
-string right truncation
-expected length 255, actual 293

[asfernandes]

SQL> SELECT cast(RDB$GET_CONTEXT('SYSTEM', 'SEARCH_PATH') as varchar(293)) FROM RDB$DATABASE;

CAST                                                                                                                                                                                                                                                                                                  
===================================================================================================================================================================================================================================================================================================== 
"TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "TEST_SCHEMA", "SYSTEM"