Database Reference
In-Depth Information
Table 24-5. CLOSE Parameters
Parameter
Meaning
c
CPU time
e
Elapsed time
dep
Recursive call depth
type
Type of close operation:
0: hard close; the cursor is not put into the server-side cursor cache
1: the cursor is cached in a previously empty slot of the server-side
cursor cache, since it executed at least 3 times
2: the cursor is placed in a slot of the server-side cursor cache at the
expense of aging out another cursor, since it executed at least 3 times
3: the cursor remains in the server-side cursor cache
tim
Timestamp
The CLOSE entry is suitable for calculating the effectiveness of the server-side cursor cache.
Oracle11 g is the first release that enables the server-side cursor cache with a default size of 50 slots.
In all prior releases the server-side cursor cache was disabled by default. The paper Designing
applications for performance and scalability ([Engs 2005]) released by Oracle Corporation in 2005
states that the scalability of applications that repeatedly soft-parse the same SQL statements
does improve with a sufficiently large value of SESSION_CACHED_CURSORS . Applications that
avoid repeated soft-parses, e.g., by enabling a client-side cursor cache, are even more scalable.
The method for enabling a client-side cursor cache depends on the Oracle API used. The
Oracle JDBC drivers include support for client-side cursor caching through the methods
setImplicitCachingEnabled and setStatementCacheSize of the class OracleConnection .
COMMIT and ROLLBACK
The ORACLE DBMS does not require clients to explicitly start a transaction. The DBMS auto-
matically opens a transaction as soon as the first data item is modified or a distributed operation,
such as a SELECT from a table via a database link is performed. The latter operation takes a TX
and a DX enqueue, which are released when COMMIT is issued. Transaction boundaries in a trace
file are marked by XCTEND entries. The minimum SQL trace level for enabling XCTEND entries is 1.
Their format is as follows:
XCTEND rlbk=[0-1], rd_only=[0-1]
Parameters used in XCTEND entries are explained in Table 24-6.
Table 24-6. XCTEND Parameters
Parameter
Meaning
rlbk
Short for rollback, rlbk=0 : COMMIT , rlbk=1 : ROLLBACK
rd_only
Read only transaction, rd_only=0 : read/write operations have occurred, rd_only=1 :
read only—no data changed
 
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