Oracle Performance Tuning Fundamentals

transcript

Carlos Sierra

Carlos Sierra •  SQLTXPLAIN + SQL Health-‐Check SQLHC + •  Consultant/Developer/DBA/Design/+ •  Oracle Performance + SQL Tuning •  Oracle Database Health-‐Check •  Tools + Scripts •  Speaker

Oracle Performance Tuning Fundamentals

•  Concepts •  Time •  Waits •  StaLsLcs •  Dynamic Views

What is Performance Tuning? •  Provide correct mix and amount of Resources •  Reduce User’s Wait Times •  Changing System components to achieve Goals

•  Increase Throughput •  Improve Response Time

Why Performance Tuning is hard? •  Concurrency •  Dynamism •  Complexity – Too many knobs to our disposal – Too many soXware layers

Performance Tuning Approaches •  “Top-‐down” •  “Bo\om-‐up” •  “HolisLc” •  “Random” a.k.a. “Trial and Error” •  “Silver Bullets” a.k.a. “One Size Fits All”

Back to Basics •  Understand your OperaLng System •  Understand your Database •  Understand your Business •  Understand your Users •  Understand your OpLons

OS Components •  CPU •  Memory •  I/O Subsystem – Disk •  Capacity and Throughput

•  Network

OS Performance Monitoring Tools •  sar •  top and htop •  mpstat and vmstat •  iotop and iostat •  dtrace and strace

OS Tools Strategy •  Define your own subset of Tools to use •  Learn them well •  Create some Scripts or use a GUI •  Correlate DB Performance to OS Monitoring •  Work with your System Administrator

OS StaLsLcs within Oracle •  Provides a high-‐level view of OS •  CumulaLve Metrics •  Views – V$OSSTAT – DBA_HIST_OSSTAT

Oracle Architecture •  Database – Data Files + Temp Files + Redo Log + Control Files

•  Instance – SGA + PGA + Processes

•  RAC

Performance is about Time •  Performance is be\er understood as Time •  Which Time? – User? – Clock? – Elapsed? – CPU?

Service Time •  Service Time = CPU Time •  User Time = CPU Time + Wait Time •  User Time = Service Time + Wait Time •  Time = Service + Wait

Wait Time •  Overhead •  Two flavors – Non-‐Idle •  Inside the database

–  Idle •  Outside the database

Non-‐idle Waits •  Overhead •  AcLvely WaiLng inside the database •  Examples – Reading a Block from Disk –  Index Rebuild – ApplicaLon Row level Lock

Idle Waits •  Overhead •  InacLve •  WaiLng for work •  Outside the database

What is a Wait Event? •  V$EVENT_NAME •  1,152 on 11.2.0.3 •  P1, P2, P3 Parameters – Oracle Database Reference •  C Oracle Wait Events

•  Categorized into 12 Wait Classes

Wait Class (1) •  AdministraLve •  ApplicaLon •  Cluster •  Commit

Wait Class (2) •  Concurrency •  ConfiguraLon •  Network •  Other

Wait Class (3) •  Queue •  Scheduler •  System I/O •  User I/O

Timed Event •  CPU + •  Non-‐idle Wait Events

Performance StaLsLcs •  If Wait Events refer to Time and Times •  Then StaLsLcs refer to Counters – How many of “X” so far (from Instance startup) – Examples •  Sorts •  Consistent Gets

StaLsLcs a.k.a. Counters •  V$STATNAME •  638 Counters on 11.2.0.3 •  DescripLon – Oracle Database Reference •  E StaLsLcs DescripLons

•  Categorized into 8 StaLsLcs Classes

StaLsLcs Classes (1) •  1, User •  2, Redo •  4, Enqueue •  8, Cache

StaLsLcs Classes (2) •  16, OS •  32, Real ApplicaLon Clusters •  64, SQL •  128, Debug

StaLsLcs Classes (3) •  A Counter belongs to 1 or more Class

Session Type and State •  Foreground Type – User Session

•  Background Type – Database Programs

•  On CPU State •  WaiLng State

Database Time •  Includes all Foreground Sessions – Currently “On CPU” or on a “Non-‐idle Wait Event”

•  Be aware – Database Time in 1hr interval can add to > 1hr –  It can also add to > (Lme interval x CPU count)

Database Time Example •  Wall Clock Time: 60 minutes •  CPU_COUNT: 12 •  CPU Time: 300 minutes (< 12 x 60 = 720) ~42% •  30 users waiLng on a Lock for 50 minutes each •  Thus: DB Time of 1,800 minutes (> 720) –  300 + (30 x 50)

Background Time •  Includes all Background Sessions – Currently “On CPU” or on a “Non-‐idle Wait Event”

System Time Model (1) •  V$SYS_TIME_MODEL •  V$SESS_TIME_MODEL •  CumulaLve Time with no wrapping •  Tree with 19 nodes – Two root nodes

System Time Model (2) •  Two root nodes – DB (Elapsed) Time – Background Elapsed Time – Notes: •  Children do not necessarily add up to the parent •  Children are not necessarily exclusive •  The union of children does not cover the whole of the parent

System Time Model (3)

1) background elapsed time 2) background cpu time 3) RMAN cpu time (backup/restore) 1) DB time 2) DB CPU 2) connection management call elapsed time 2) sequence load elapsed time 2) sql execute elapsed time 2) parse time elapsed 3) hard parse elapsed time 4) hard parse (sharing criteria) elapsed time 5) hard parse (bind mismatch) elapsed time 3) failed parse elapsed time 4) failed parse (out of shared memory) elapsed time 2) PL/SQL execution elapsed time 2) inbound PL/SQL rpc elapsed time 2) PL/SQL compilation elapsed time 2) Java execution elapsed time 2) repeated bind elapsed time

Response Time •  Time a Query takes to return First Row(s) •  Important for Online oriented processing – OLTP behavior

Throughput •  Amount of Work performed in a given Time – How many Rows this Query returns per Second? – Time a Query takes to return All Rows

•  Important for Batch oriented processing – Data warehouse behavior

User Time •  A measure of User Experience – Time it takes for a User to get some Result

•  Includes – Database Time – Scheduling Time – Network Time

Which Time is more important? •  Database? •  Background? •  Service? •  Wait? •  Response? •  User?

Processes and Sessions •  ConnecLon is a pathway to the Database •  A ConnecLon can have 0, 1 or more Sessions •  A Process may serve 1 or more Sessions •  Default Sessions –  (1.5 x Processes) + 22

How many Processes to have? •  Ideally between 2 and 5 Lmes the number of CPUs – Example: 16 CPUs •  Ideally: between 32 and 80 •  Common: ~1000

•  Advice: – Keep “processes” parameter as small as possible

Average AcLve Session (AAS) •  Common unit to compare Performance •  What is an “AcLve Session”? – One “On CPU” or on a “Non-‐idle Wait Event”

•  Two ways to compute AAS 1.  Using count of AcLve Sessions on a Snapshot 2.  Database Time divided over Wall Clock Time

WORKLOAD REPOSITORY report for DB Name DB Id Instance Inst Num Startup Time Release RAC -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐ XXX 1319103893 XXX 1 10-‐Apr-‐14 14:55 11.2.0.3.0 NO Host Name Platform CPUs Cores Sockets Memory(GB) -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐ -‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ xxxxxxxx AIX-‐Based Systems (64-‐bit) 16 4 72.00 Snap Id Snap Time Sessions Curs/Sess -‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐ Begin Snap: 139 11-‐Apr-‐14 15:00:58 217 144.9 End Snap: 140 11-‐Apr-‐14 15:15:58 218 145.7 Elapsed: 15.01 (mins) DB Time: 83.46 (mins) Cache Sizes Begin End ~~~~~~~~~~~ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ Buffer Cache: 23,360M 23,360M Std Block Size: 8K Shared Pool Size: 1,664M 1,664M Log Buffer: 11,848K Load Profile Per Second Per Transaction Per Exec Per Call ~~~~~~~~~~~~ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ DB Time(s): 5.6 1.7 0.02 0.11 DB CPU(s): 0.2 0.1 0.00 0.00 Redo size: 238,783.6 72,491.8 Logical reads: 2,300.9 698.5 Block changes: 626.3 190.2 Physical reads: 3.9 1.2 Physical writes: 28.8 8.7 User calls: 48.4 14.7 Parses: 14.3 4.3 Hard parses: 0.0 0.0 W/A MB processed: 0.1 0.0 Logons: 0.1 0.0 Executes: 317.3 96.3 Rollbacks: 1.1 0.3 Transactions: 3.3

Performance Tuning Goals •  Minimize amount of Business required work •  OpLmize CPU Time – Avoid wasLng cycles

•  OpLmize Wait Time – Minimize Wait Time

•  Judged by Business and by User community

Basic DB Performance CollecLon •  System-‐wide Waits – CumulaLve

•  Session Waits – CumulaLve and Current

•  Session and System-‐wide StaLsLcs Counters – CumulaLve

Dynamic Performance Views (1) •  V$SESSION_WAIT – Current or last Wait •  Only one row per Session •  P1, P2 and P3 provide details of Wait

– Available also on V$SESSION

Dynamic Performance Views (2) •  V$SESSION_EVENT – Total Waits and Time Waited per Event – Only those Events the Session has waited on

Dynamic Performance Views (3) •  V$SESSION_WAIT_CLASS – Total Waits and Time Waited per Wait Class – Aggregate of V$SESSION_EVENT on Wait Class

Dynamic Performance Views (4) •  V$SESSTAT – StaLsLcs a.k.a. Counters (not Waits) – SID, staLsLcs# and value –  Join to V$STATNAME

Dynamic Performance Views (5) •  V$SYSTEM_EVENT – Total Waits and Time Waited per Event – Aggregate of V$SESSION_EVENT –  Instance-‐wide

Dynamic Performance Views (6) •  V$SYSTEM_WAIT_CLASS – Total Waits and Time Waited per Wait Class – Aggregate of V$SYSTEM_EVENT on Wait Class; or – Aggregate of V$SESSION_WAIT_CLASS

Dynamic Performance Views (7) •  V$SYSSTAT – staLsLcs#, name, class and value – No need to join to V$STATNAME – Aggregate of V$SESSTAT

Dynamic Performance Views (8) •  V$SESS_TIME_MODEL •  V$SESSMETRIC •  V$SESS_IO •  V$SESSION_LONGOPS

Dynamic Performance Views (9) •  V$SYS_TIME_MODEL •  V$SYSMETRIC •  V$SYSMETRIC_SUMMARY •  V$SYSMETRIC_HISTORY

Dynamic Performance Views (10) •  V$EVENT_HISTOGRAM •  V$EVENTMETRIC •  V$WAITCLASSMETRIC •  V$WAITCLASSMETRIC_HISTORY

Dynamic Performance Views (11) •  V$FILEIO •  V$FILE_HISTOGRAM •  V$FILE_METRIC •  V$FILEMETRIC_HISTORY

Dynamic Performance Views (12) •  V$OSSTAT •  V$PGASTAT •  V$SGASTAT

•  And many more…

Dynamic Views Summary •  V$SYSTEM_EVENT – Total Waits for Events (system-‐wide)

•  V$SESSION_EVENT – Total Waits for Events (session specific)

•  V$SESSION_WAIT – Current or Last Wait (session specific)

Real-‐life use of Dynamic Views •  SQL*Plus Scripts – Your own or Tanel Poder’s “snapper.sql”

•  Current and legacy Tools – OEM, AWR, ADDR, ASH, Statspack, bstat/estat

•  Other Scripts and Tools

AutomaLc Workload Repository (AWR)

•  Requires Oracle DiagnosLcs Pack License •  112 DBA_HIST Views on 11.2.0.3 •  Snapshots – One hour interval (default) – One week retenLon (default)

AcLve Session History (ASH) •  Requires Oracle DiagnosLcs Pack License •  MulL-‐dimension •  V$ACTIVE_SESSION_HISTORY – One snapshot (sample_id) every second

•  DBA_HIST_ACTIVE_SESS_HISTORY – One sample_id out of every 10

Methodology in a Nut Shell •  Listen to the voice of the Business •  Collect DiagnosLcs and compare to Baselines •  IdenLfy Pain and Bo\lenecks •  MiLgate Pain by addressing Bo\lenecks – Reach out when needed – Learn and document

Database Temperature Rule of Thumb

•  If (Database + Background) Time < Interval è ice cold < Interval x CPU count è cold < 5 x Interval x CPU count è warm < 10 x Interval x CPU count è hot > 10 x Interval x CPU count è melLng

Warning •  Take “Rules of Thumb” with a pinch of salt and do not confuse them with “Myths”

•  Rule of Thumb “a principle with broad applica7on that is not intended to be strictly accurate or reliable for every situa7on”

•  Myth “a widely held but false belief or idea”

Some Myths (1) •  Change nothing and Performance will remain the same (i.e. Freeze CBO StaLsLcs)

•  Parallelize as much as possible and everything will run faster

•  Improve Buffer Hit RaLo and Performance will improve

Some Myths (2) •  An Index Access operaLon is be\er than a Full Table Scan

•  Placing Tables and Indexes on separate Tablespaces provides be\er performance

•  Reorganize all Indexes periodically for be\er performance

Some Myths (3) •  Upgrading to faster CPUs results on be\er performance

•  Allocate to Oracle more Memory and Processes run faster

•  Segments (Tables or Indexes) with one Extent perform be\er

Some Myths (4) •  SQL cannot be modified (canned applicaLon) •  A truncated SQL Trace cannot be used for DiagnosLcs

•  Top-‐5 Wait Events show the root cause of the poor Performance

•  Silver Bullets are sound and reliable

Conclusions •  User Experience should be the driver – AuthenLc Business Requirements

•  QuesLon Everything – Apply ScienLfic Method: Test, Prove or Debunk

•  Balance between broad with deep analysis •  Diagnose with sound Scripts and Tools

References •  Oracle Database Reference 11g Release 2 •  Oracle Database Concepts 12c Release 1 •  Snapper -‐ Tanel Poder – h\p://blog.tanelpoder.com/files/scripts/snapper4.sql

Contact InformaLon •  carlos.sierra@enkitec.com •  carlos-‐sierra.net •  @csierra_usa

Oracle Performance Tuning Fundamentals

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