Finding the Performance Bottlenecks in Your Application Ian Jones and Roger Schrag Database Specialists, Inc. IOUG-A Live! 1999 Paper #158

Finding the Bottleneck: Half the Battle in Tuning One bad SQL statement can spoil performance Too much code to take the “let’s tune every statement” approach DBA can’t be familiar with every line of code

Zero in on the Bottleneck Use the v$ views Use SQL Trace and timed statistics Use GUI tools

Today’s Presentation Half a dozen real-life examples –scenario –command-line efforts –resolution Demo of GUI tools –Enterprise Manager –freeware

The Terrifyingly Slow EDI Load A transportation company used EDI to exchange data with customers. They loaded EDI files into a temp table with SQL*Loader and then ran a 1500 line PL/SQL stored procedure to validate the data and update application tables. As more customers began sending EDI files, the PL/SQL stored procedure could no longer keep up. Data validation took as long as 24 hours for some EDI files. Where do we start tuning?

Start Load Process and Identify the Database Session SQL> SELECT sid, serial#, status, username, osuser, 2 module, action 3 FROM v$session; SID SERIAL# STATUS USERNAME OSUSER MODULE ACTION ACTIVE oracle 2 1 ACTIVE oracle 3 1 ACTIVE oracle 4 1 ACTIVE oracle 5 1 ACTIVE oracle 6 1 ACTIVE oracle ACTIVE BJENKINS bjenkins de INACTIVE RTHOMAS rthomas de INACTIVE EJOHNSON ejohnson de ACTIVE EDI_LOAD edi SQL*Plus validate

View the Statement Being Executed SQL> SELECT B.sql_text 2 FROM v$session A, v$sqlarea B 3 WHERE A.sid = 45 4 AND B.address = A.sql_address; SQL_TEXT SELECT ITEM_ID FROM ITEM_TRANSLATIONS WHERE SOURCE_ID = :b1 AND SUBSTR(SOURCE_SKU_CODE,1,6) = :b2 AND SYSDATE BETWEEN START_DATE_ACTIVE AND NVL (END_DATE_ACTIVE, SYSDATE)

We Found a Bottleneck! PROCEDURE edi_validate_and_load (p_cust_id IN NUMBER) IS CURSOR c_get_item_id (cp_cust_id IN NUMBER, cp_sku IN VARCHAR2) IS SELECT item_id FROM item_translations WHERE source_id = cp_cust_id AND source_sku_code LIKE cp_sku || '%' AND SYSDATE BETWEEN start_date_active AND NVL (end_date_active, SYSDATE);

Disk Array Far Too Busy One third of a financial institution’s loan processing department started using a new PowerBuilder application. Response time was acceptable, but disk utilization on the server was at 100%. What could be done to reduce I/O so that the response time will still be acceptable after the rest of the department starts using the new application?

Identify the SQL Statements Causing the Most Disk Reads SELECT sql_text, disk_reads, executions, disk_reads / DECODE (executions, 0, 1, executions) reads_per_exec FROM v$sqlarea ORDER BY reads_per_exec; SELECT sql_text, disk_reads, executions, disk_reads / DECODE (executions, 0, 1, executions) reads_per_exec FROM v$sqlarea ORDER BY disk_reads; SELECT sql_text, buffer_gets, executions, buffer_gets / DECODE (executions, 0, 1, executions) gets_per_exec FROM v$sqlarea ORDER BY buffer_gets;

Part of the Query Results… SQL_TEXT DISK_READS EXECUTIONS READS_PER_EXEC SELECT P.PRODUCT_DESC, CP.PRODUCT_ID, UPPER (:b1) CLIENT_ID FROM CLIENT_PRODUCT CP, PRODUCT P WHERE CP.PRODUCT_ID = P.PRODUCT_ID AND (UPPER (CP.CLIENT_ID), CP.VALID_CLIENT_LEVEL_ID) IN (SELECT UPPER (:b1), CA.VALID_CLIENT_LEVEL_ID FROM CLIENTS C, CLIENT_ADDRESS CA WHERE UPPER (C.CLIENT_ID) = UPPER(:b1) AND C.CLIENT_ID = CA.CLIENT_ID)

The Same Query Formatted for Readability SELECT P.product_desc, CP.product_id, UPPER (:b1) client_id FROM client_product CP, product P WHERE CP.product_id = P.product_id AND (UPPER (CP.client_id), CP.valid_client_level_id) IN (SELECT UPPER (:b1), CA.valid_client_level_id FROM clients C, client_address CA WHERE UPPER (C.client_id) = UPPER(:b1) AND C.client_id = CA.client_id) A case-insensitive query turns out to be very inefficient. Now we know what to tune.

The So-Called “Locking Problem” A developer coded a PL/SQL function called compute_irr for computing internal rate of return. Response times varied widely. The developer claimed there was a locking problem on the database. What caused the slow performance in compute_irr?

SQL> SELECT sid, serial#, status, username, osuser, 2 module, action 3 FROM v$session; SID SERIAL# STATUS USERNAME OSUSER MODULE ACTION ACTIVE oracle 2 1 ACTIVE oracle 3 1 ACTIVE oracle 4 1 ACTIVE oracle 5 1 ACTIVE oracle 6 1 ACTIVE oracle INACTIVE GL swatkins INACTIVE APPLSYS applmgr ACTIVE RSCHRAG rschrag SQL*Plus INACTIVE FA rschrag SQL*Plus Start SQL*Plus and Identify the Database Session

Check Session Statistics Before Calling compute_irr SQL> SELECT A.name, B.value 2 FROM v$statname A, v$sesstat B 3 WHERE B.statistic# IN (12, 37, 38, 39, 119, 123, 4 139, 140, 141) 5 AND B.sid = 63 6 AND A.statistic# = B.statistic#; NAME VALUE CPU used by this session 1292 db block gets consistent gets physical reads 346 table scans (long tables) 0 table scan rows gotten 1054 sorts (memory) 826 sorts (disk) 0 sorts (rows) 4693

Check Session Statistics Again While compute_irr Is Running SQL> SELECT A.name, B.value 2 FROM v$statname A, v$sesstat B 3 WHERE B.statistic# IN (12, 37, 38, 39, 119, 123, 4 139, 140, 141) 5 AND B.sid = 63 6 AND A.statistic# = B.statistic#; NAME VALUE CPU used by this session 7274 db block gets consistent gets physical reads 346 table scans (long tables) 0 table scan rows gotten 1054 sorts (memory) 826 sorts (disk) 0 sorts (rows) 4693

Compute the Deltas Look for an infinite loop that involves no SQL statements.

Where Is the I/O Coming From? An application that performed well in a demo database quickly became I/O-bound when a significant amount of data was loaded into the database. It seemed as if there was a huge amount of I/O even with no users logged on to the application. What could be causing so much I/O activity?

Look at Physical Reads Instance-Wide and Per Session SQL> SELECT name || ' (instance-wide)', value 2 FROM v$sysstat 3 WHERE statistic# = 39 4 UNION ALL 5 SELECT 'sid = ' || TO_CHAR (sid), value 6 FROM v$sesstat 7 WHERE statistic# = 39;

And the Results Are... NAME VALUE physical reads (instance-wide) sid = 1 0 sid = 2 0 sid = 3 0 sid = 4 0 sid = 5 0 sid = sid = sid = 8 0 sid = sid = sid = sid =

Investigate Suspicious Session 13 SQL> SELECT sid, serial#, status, username, osuser, 2 module, action 3 FROM v$session 4 WHERE sid = 13; SID SERIAL# STATUS USERNAME OSUSER MODULE ACTION ACTIVE APPSCHEMA daemon EXTRACT GET SQL> SELECT A.name, B.value 2 FROM v$statname A, v$sesstat B 3 WHERE B.statistic# IN (12, 37, 38, 39, 119, 123, 4 139, 140, 141) 5 AND B.sid = 13 6 AND A.statistic# = B.statistic#;

Suspicious Session 13 (continued) NAME VALUE CPU used by this session 0 db block gets consistent gets 293 physical reads table scans (long tables) 575 table scan rows gotten sorts (memory) 3 sorts (disk) 0 sorts (rows) 4210

What SQL Is Session 13 Executing? SQL> SELECT B.sql_text 2 FROM v$session A, v$sqlarea B 3 WHERE B.address = A.sql_address 4 AND A.sid = 13; SQL_TEXT SELECT * FROM TRANSACTIONS WHERE EXTRACTED = 'N’ Let me guess! The transactions table is about 10,000 blocks in size and the extracted column is not indexed.

“Fast” Reports That Were Too Slow A software vendor built an application using Oracle, Developer/2000, and a third-party reporting tool. A key report took about six seconds to complete, but consider that users will run the report in batches of several thousand. The report has thousands of lines of spaghetti code. How do you figure out what's slowing it down?

Build a Version of the Report That Enables SQL Trace DECLARE c INTEGER; i INTEGER; BEGIN c := dbms_sql.open_cursor; dbms_sql.parse (c, 'ALTER SESSION SET TIMED_STATISTICS=TRUE', dbms_sql.native); i := dbms_sql.execute (c); dbms_sql.close_cursor (c); dbms_session.set_sql_trace (TRUE); END; Trace only what you need to trace!

Run the Report, Fetch the Trace File, Run TKPROF On It OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS call count cpu elapsed disk query Parse Execute Fetch total Misses in library cache during parse: 30 Look into using bind variables to reduce parsing.

The Chameleon Application An application ran well on a test database loaded with a full set of production data. But when the application was deployed in production, queries took over a minute to complete. In the test environment these same queries completed in under ten seconds. Policies forbid modifying code in production. What could be causing the application to run slower in production?

Find a Power User to Reproduce the Slow Behavior Identify the database session: SQL> SELECT sid, serial#, status, username, osuser, 2 module, action 3 FROM v$session 4 WHERE username = 'MARYD'; SID SERIAL# STATUS USERNAME OSUSER MODULE ACTION INACTIVE MARYD mbd frontend query

Enable Timed Statistics Temporarily SQL> ALTER SYSTEM SET TIMED_STATISTICS = TRUE; System altered. SQL>

Enable SQl Trace Just Before the Query Is Launched SQL> BEGIN 2 dbms_system.set_sql_trace_in_session (17, 9172, TRUE); 3 END; 4 / PL/SQL procedure successfully completed. SQL>

Disable SQL Trace When the Query Is Finished SQL> BEGIN 2 dbms_system.set_sql_trace_in_session (17, 9172, FALSE); 3 END; 4 / PL/SQL procedure successfully completed. SQL> SQL> ALTER SYSTEM SET TIMED_STATISTICS = FALSE; System altered. SQL>

Fetch the Trace File and Run TKPROF call count cpu elapsed disk query current rows Parse Execute Fetch total Misses in library cache during parse: 1 Optimizer goal: RULE Parsing user id: 142 (BUILD4P2) Rows Execution Plan SELECT STATEMENT GOAL: RULE 0 MERGE JOIN (OUTER) 254 SORT (JOIN) 115 NESTED LOOPS (OUTER) 253 NESTED LOOPS (OUTER) 254 TABLE ACCESS GOAL: ANALYZED (BY ROWID) OF 'MNME' INDEX GOAL: ANALYZED (FULL SCAN) OF 'MNME_I1' (UNIQUE) 253 TABLE ACCESS GOAL: ANALYZED (BY ROWID) OF 'LCONTYPE' 254 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF 'LCONTYPE_PK' (UNIQUE) 115 TABLE ACCESS GOAL: ANALYZED (BY ROWID) OF 'MTAX' 254 INDEX GOAL: ANALYZED (UNIQUE SCAN) OF 'MTAX_I1' (UNIQUE) 129 SORT (JOIN) 129 TABLE ACCESS GOAL: ANALYZED (FULL) OF 'LPOST’ The optimizer can behave differently from one Oracle version to the next.

GUI Tools Demo

To Find the Bottlenecks in Your Applications: Monitor v$sqlarea Monitor v$sysstat and v$sesstat Use SQL Trace judiciously Consider using GUI tools

Resources Oracle Server Tuning - Overview of the tuning process - How to use SQL Trace and TKPROF Oracle Server Reference - Descriptions of all v$ views High Performance SQL Tuning by Guy Harrison - Lots of tuning tips - Discussion of GUI tools available on the Internet Download this presentation - Download a companion white paper

Contact Information Ian Jones: Roger Schrag: Database Specialists, Inc. 388 Market Street, Suite 400 San Francisco, CA /