Open and closed cursor

Question

I have some doubts/questions .
What is the difference between open and closed cursor?
Are library cache locks same as parse locks?
What is the difference between latch and mutex?
I would be grateful if experts could answer these questions.
Regards

Answer 1

Almost correct. The terminology is however nor correct.
Simplistically:
The SQL engine receives a SQL. It attempts a soft parse first. This means looking for an existing cursor in the Shared Pool with the same SQL. This existing cursor can be in use by other sessions. It does not matter - if that cursor is in used (opend by other sessions), or not. It may not be in use at all and simply sitting there in the cache. If such a cursor is found, it is used for that session's SQL - and that session gets a cursor handle (reference/pointer) to that existing cursor.
If the SQL engine does not find an existing cursor to use, it needs to create a brand new cursor in the Shared Pool. This is a hard parse. Again, the session receives a cursor handle for that new cursor created.
And that is it.
You now need to decide how to use that cursor handle. The cursor itself is a program. You have a handle to execute that cursor program. Via its bind interface you can input data to this cursor program. Then execute it and receive (fetch) output of that cursor program.
So the ideal is to re-use the cursor handle again and again.
Basic example: the following is not optimal as the same cursor is opened and closed, opened and closed, for each read from the file. A lot of soft parsing results.
while not-eof( filehandle )   // read data from a file
  read file data into var1, var2
  open cursor for 'insert into testtab values( :1, :2)'   // create a cursor
  bind cursor :1 = var, :2 = var2  // bind values to cursor (for insert)
  exec cursor // do SQL insert
  close cursor 
end whileThis is a lot better. A single cursor is used and executed again and again:
open cursor for 'insert into testtab values( :1, :2)'   // create a cursor
while not-eof( filehandle )   // read data from a file
  read file data into var1, var2
  bind cursor :1 = var, :2 = var2  // bind values to cursor (for insert)
  exec cursor // do SQL insert
end while
close cursor  In this case a single soft/hard parse - and the client uses that cursor handle to execute that cursor (insert data) program again and again.