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| Monitor Oracle Resource Consumption in UNIX |
| 摘自oracle官方网站 |
PURPOSE ======= This article is intended to provide DBAs an overview of the resources consumed by Oracle, and the tools commonly used to monitor the resource consumption. SCOPE & APPLICATION =================== Database performance is bounded by the system resources. Sometimes, poor database performance can be caused by faulty configuration of the instance and database. Sometimes, it can be caused by abnormal resource consumption by an Oracle transaction, user, or process. It is essential for DBAs to proactively monitor the resource consumption, and take any corrective actions before potential serious impacts. Memory, CPU, and I/O are the three most common resources consumed by Oracle. We will discuss these resources, and list some of the commonly used tools that monitor them. These resources can be monitored at both Oracle Server and Operating System levels. DBAs should acquire any detailed information about the OS tools from the System Administrators or OS vendors. OVERVIEW ======== Oracle Instance --------------- An Oracle Instance is a set of System Global Area and background processes. It is started during �startup nomount�. The characteristics of an instance are: - Its name is defined by environmental variable ORACLE_SID. - It is started based on the configurations defined in init<SID>.ora file. - It has its own set of SGA and background processes. - It can only belong to one database at one time. - Multiple instances can access the same database in OPS configuration. There can be multiple oracle instances from the same $ORACLE_HOME. They are only limited by the OS resources, such as disk, memory, kernel parameters, etc. Each time an instance is started, the OS is being asked to give some key resources according to the parameters specified in init<SID>.ora for that instance. Each Oracle instance has two main areas of memory structures, System Global Area (SGA) and Program Global Area (PGA) for background processes. SYSTEM RESOURCES ================ Memory ------ There are several memory structures used by Oracle, SGA, PGA, UGA, and sort area. 1) Shared Memory & Semaphores Oracle uses shared memory for efficiency. The OS does not have to load up the same address page(s) into the memory each time a process needs to reference it. Instead the process can just reference the one memory location, read/write to it, and then leave. Therefore, the data is not moved from one process's memory address space to another. In order to control memory integrity so that only one process is accessing that memory address, semaphores are used. Semaphores have only two values, set or unset. When a process goes to reference a memory location, it first checks to see if the semaphore allocated for that memory location is set. If so, it waits until that semaphore location is free. Once available, it will first 'set' the semaphore so to not allow other processes to interrupt or corrupt the current processes read/write. The size of the SGA is made up by shared pool, database buffer cache, redo log buffer, large pool, and java pool. A commonly used formula to calculate the size of the SGA is: ((db_block_buffers * block size) + (shared_pool_size + large_pool_size + java_pool_size + log_buffers) + 1MB See more detailed information in <Note:1008866.6> How to determine SGA Size (7.x, 8.0, 8i, 9i). For optimal database performance, SGA should fit into real memory, and avoid swapping. The size of the SGA is also bounded by OS kernel parameters, such as SHMMAX in Unix. To learn more about shared memory, see <Note:1011658.6> Shared memory requirement on Unix. Since the SGA can be accessed by all processes that have been allocated, this is used to allow multiprocessing and access between processes within the SGA. A few of the common semaphores and shared memory segments that Oracle uses are: - SEMMNI => Max number of semaphores sets/identifiers - SEMMNS => Max number of semaphores in system - SHMMNI => Number of shared segments identifiers to be pre-allocated - SHMMAX => Max shared segment size For more information, see <Note:15566.1> Unix Semaphores and Shared Memory Explained. Also see the corresponding Oracle Installation Guide for your release of Oracle, that indicate minimum values for semaphore and shared memory. 2) Private Memory PGA is a memory region containing data and control information for a single server or background process. The size of PGA depends on the database configuration, and what the process does. In a dedicated server configuration, where one server process interacts with one user process, PGA contains stack space and UGA. UGA is made up by user session data, cursor state, and sort area. In a multithreaded server configuration, where one shared server is shared by multiple user processes, UGA is part of the shared pool. The PGA exists as: - Nonshared memory area to which a process can write - One PGA is allocated for each server or background process - Once the user has connected, a user can never run out of PGA space. Otherwise the connection will not happen and may result in an ora-4030 error. Oracle parameters that affect the sizes of PGA are: - open_links - db_files - sort_area_retained_size - sort_area_size To calculate the current PGA size: SESSION PGA MEMORY => Statistic containing the current PGA size for a session SESSION PGA MEMORY MAX => Statistic containing the peak PGA size for a session PGA = dedicated server processes - UGA = Client machine process To view a listing of the UGA and PGA memory for every session, see <Note:1070975.6> TFTS: LISTING MEMORY USED BY ALL SESSIONS Note: On the RS/6000, each shadow process stores its PGA in a shared memory segment. The size of the stack space in each PGA created on behalf of Oracle background processes (such as DBWR and LGWR), is affected by some additional parameters. CPU --- CPU consumption varies with the activities of the processes. During the peak workload, the DBAs and the SAs may see CPU utilization go up to 90%. In general the DBAs should balance the workload to avoid overloading the system. I/O --- The amount of I/O occurrence also depends on the activities of the processes. While memory I/O may be necessary, disk I/O should be minimized. To avoid disk I/O contention, files should be distributed across devices. Some of the background processes can be I/O intensive, such as DBWn, LGWn, ARCn, and CKPT. In some situations, DBAs may find multiple DBWn/ARCn, or DBWR/ARC0/LWGR I/O slaves beneficial. MONITORING AT THE SERVER LEVEL ============================== V$ dynamic performance views capture the cumulative statistics of resource consumptions, at both system or session levels. STATSPACK and Utlbstat/utlestat reports summarize the statistics from these v$ views for a defined period of time for the database and tkprof utility reports statistics at query level. Init<SID>.ora parameter TIMED_STATISTICS should set to be true. The descriptions of v$ views are in Oracle 7/8/8i/9i Server Reference manual. To learn more about analyzing STATSPACK or utlbstat/utlestat reports, see <Note:94224.1> StatsPack FAQ and <Note:62161.1> Systemwide Tuning using UTLESTAT Reports in Oracle7/8 To learn more about interpreting tkprof output, see Note <Note:32951.1> :Tkprof Interpretation. Examples -------- The following examples shows the output from all different tools available in Oracle to get this information: - STATSPACK and bstat/estat reports Statistic Total Per Transact Per Logon Per Second ---------------------------- ------------- ---------------------- ----------------- ------------------ CPU used by this session 2278466 222.59 1974.41 203.6 CPU used when call started 2239857 218.82 1940.95 200.15 CR blocks created 2938 .29 2.55 .26 session pga memory 7138227 34521 991 191 session pga memory max 40327524 745091 98305 756 session uga memory 326143 96312 57843 654 session uga memory max 2483564 185735 12386 700 - tkprof .prf output file OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS call count cpu elapsed disk query current rows ------------ --------- --------- ------------ ---------- ----------- ------------ ---------- Parse 3 0.04 0.05 0 0 0 0 Execute 4 0.00 0.05 0 0 0 0 Fetch 2 0.00 0.06 2 17 68 1 ------------ --------- --------- ------------ ---------- ----------- ------------ ---------- total 9 0.04 0.16 2 17 68 1 - Scripts output REM Monitor memory usage SQL> select sid, name, value 2 from v$statname n, v$sesstat s 3 where n.statistic# = s.statistic# 4 and n.name like '%memory%' 5 order by sid; SID NAME VALUE --------- --------------------------------- ---------- 1 session uga memory 18252 1 session uga memory max 18252 1 session pga memory max 59568 1 sorts (memory) 0 1 session pga memory 59568 . . REM monitor CPU usage SQL> select sid, name, value 2 from v$statname n, v$sesstat s 3 where n.statistic# = s.statistic# 4 and n.name like '%cpu%' 5 order by sid; SID NAME VALUE --------- ------------------------------ ---------- 1 recursive cpu usage 0 1 parse time cpu 0 1 OS Wait-cpu (latency) time 0 . . REM monitor I/O SQL> select file#, phyrds, phywrts 2 from v$filestat; FILE# PHYRDS PHYWRTS ------------ -------------- ---------------- 1 3239 141 2 80 246 3 9 163 4 6 3 5 5 3 . . MONITORING AT THE OPERATING SYSTEM LEVEL ========================================= OS Semaphores ------------- Each Oracle instance needs to have a set amount of semaphores. The total amount of semaphores required is derived from the 'processes' parameter inside that Oracle instance init.ora file. As more instances and/or databases are added the OS kernel parameter SEMMNS will need to be adjusted accordingly. For more information, see <Note:145179.1>Semaphore Calculations - Estimating semaphore sets/semaphores for an Instance. Ulimits -------- Refer to the install guide for the basic kernel parameters that need to be set. When increasing the amount of instances & databases on this Unix server, one will need to increase the kernel parameters accordingly. To check the Unix oracle user id limits: % ulimit -Sa (This is the output you may expect to see) time(seconds) unlimited file(blocks) unlimited data(kbytes) unlimited stack(kbytes) unlimited memory(kbytes) unlimited coredump(blocks) 2097151 nofiles(descriptors) unlimited Monitoring Tools --------------------- Commonly used tools are vmstat, iostat, pstat, size, ipcs, ps, sar, and other OS specific tools. View the manual page to obtain the usage and column descriptions. Here are a few specific Unix supplied tools to help monitor different OS activities: 1) Memory: To see how much memory is currently being used, vmstat (virtual memory statistics) focuses mainly on CPU and memory. OS Command ~~~~~~~~~~ ~~~~~~~~~ Sun Solaris: vmstat HP: vmstat -n IBM: /bin/vmstat Compaq: /sbin/hwmgr Linux: xosview For specific examples of diagnosing memory on various platforms: HPUX --> see <Note:166490.1> Diagnosing Oracle memory on HP using GLANCE AIX --> see <Note:166491.1> Diagnosing Oracle Memory on AIX using SVMON SUN -->see <Note:163763.1>Diagnosing Oracle memory on Sun Solaris using PMAP 2) I/O: You should regulary monitor disk I?O statistics by using utilities such as "sar -d" or "iostat". Average service times of 50ms or lessare reason for concern if it continues over a long time. One of the goals should be minimizing disk I/O by balancing the load on the disks. To watch over disk space usage, at the Unix prompt issue the command: df -k Look at where the datafiles and ORACLE_HOME are mounted. Pay attention to how much space is available. General rule of thumb is to never allow these mount points get to 90% full (i.e. 10% available). 3) CPU utilization: OS Command ~~~~~~~~~~ ~~~~~~~~~ Sun Solaris: sar -u IBM: ps av (or) iostat 3 20 Digital: /usr/sbin/pset_info Linux: xosview In addition of monitoring the CPU usage you should monitor the runqueue to determine if processes are waiting for an available processor. You can use "sar -q" to monitor the runqueue. 4) To see how much CPU time is being used by each processor on a multiprocessor machine: OS Command ~~~~~~~~~~ ~~~~~~~~~ Sun Solaris: /usr/bin/mpstat HP: /usr/sbin/sar -M 5 5 IBM: vmstat -> Under cpu, if "us" is a very high number you have a cpu intensive process 5) To see the number of CPUs there are in the machine, and their status: OS Command ~~~~~~~~~~ ~~~~~~~~~ Sun Solaris: /usr/sbin/mpstat HP: /usr/sbin/sar -M 2 2 IBM: /usr/sbin/bindprocessor -q Digital: /usr/sbin/psrinfo -v Linux: xosview 6) To see the amount of swap space is on the machine and the usage: OS Command ~~~~~~~~~~ ~~~~~~~~~ Sun Solaris: /etc/swap -l and /etc/swap -s HP: /etc/swapinfo -m ( must be root Unix id) IBM: lsps -a Digital: /usr/sbin/swapon -s Linux: free -t 7) To see the current usage of shared memory & semephores: "ipcs -b" |
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