Parsing in Oracle

Question

Hi,
I understand hard and soft parsing but what is no parsing in Oracle. When it happens.?
Thanks.

Answer 1

888098 wrote:
I understand hard and soft parsing but what is no parsing in Oracle. When it happens.?When a cursor handle is reused. Consider the following examples (could be clients written in anything from Java to Cobol):
while not EOF( fileHandle ) loop
  read fileRecord
  cursorHandle = ParseCursor( 'insert into footab values( :1, :2 )' )
  BindCursor( cursorHandle, 1, fileRecord.field1 )
  BindCursor( cursorHandle, 1, fileRecord.field2 )
  ExecCursor( cursorHandle )
  CloseCursor( cursorHandle )
loop endThe above example parses a cursor for each loop iteration. The cursor uses bind variables and this results in a shareable SQL - which is a "good thing". The 1st parse is likely to be a hard parse. Each subsequent loop iteration is a soft parse.
However, despite the soft parsing being better than hard parsing, not parsing at all is better. The client can simply parse the SQL once and then reuse its cursor handle. E.g.
cursorHandle = ParseCursor( 'insert into footab values( :1, :2 )' )
while not EOF( fileHandle ) loop
  read fileRecord
  BindCursor( cursorHandle, 1, fileRecord.field1 )
  BindCursor( cursorHandle, 1, fileRecord.field2 )
  ExecCursor( cursorHandle )
loop end
CloseCursor( cursorHandle )In this sample code the cursor is parsed (hard or soft), once. The client then simply reuses the cursor handle in the loop. And closes the cursor handle when done. This approach is faster and results in less work for the database.
PL/SQL's optimiser also supports the above approach of reusing a cursor handle as far as I know (optimising PL/SQL code to reuse cursor handles).
The bottom line is that parsing a cursor is unavoidable. You need a hard or soft parse to create a cursor handle. However, you should not parse unnecessarily. Reuse cursor handles where possible.