The Answer to Free Memory, Swap, Oracle and everything

A presentation about using memory where it’s needed mostChristo Kutrovsky

The Pythian Group

2007 April

The Answer to Free Memory, Swap, Oracle and everything

A presentation about using memory where it’s needed mostChristo Kutrovsky

The Pythian Group

2007 April

The 45 minutes version

Who Am I?

Joined Pythian in 2003 Became team lead for one of Pythian's service

delivery teams in 2006 Notable clients: Palm Coast Data,

Freshdirect.com Presented at Collaborate '06, '07, RMOUG Special interest in 11g, RAC, Disk IO

performance, and memory Pythian's delegate to the 11g beta, participated at

the camp level (two visits)

Who is Pythian?

Provides turnkey global data architecture and operations teams on a linear-cost-to-effort basis

Founded in 1997, headquartered in Ottawa, Canada, with offices in India and Australia

Supporting almost 100 clients worldwide and more than 600 production databases

Almost 50 production engineers engaged in client service delivery

Broad data infrastructure expertise primarily focused on Oracle, Microsoft SQL Server, and MySQL on enterprise hardware

Agenda

Types of memory Virtual Memory areas How do we monitor memory usage

And make sense of it Oracle examples Case studies

Questions

How many developers How many managing linux How many managing unix (AIX, solaris) How many have root access How many have control of database

memory consumption

Terminology

What is memory The ability of a computer system to store data

Types of Memory

Short term RAM (memory)

Long term (“permament”) Disk, tape (storage)

Types of Memory - physical

CPU Registers fastest, very limited

CPU Cache (L1/L2/L3) some latency, LRU maintained

RAM major latency (relatively), partially LRU

Disk do something else while you wait

What is RAM

Faster, temporary storage A work area A place where you put your data while

you process it

The Many caches

CPU

CPU Registers2 ns CPU

Cache8 ns1:4

Main Memory (RAM)100ns1:12

Disk – Long term memory3’000’000 ns

1:30’000

TAPE – even longer

CPU Cache & CPU Registers

CPU Registers – your two hands (or more) You use them to hold the items while you

work on them CPU Cache – your desk

You use it as a quickly accessible location to store your most used items

Represents your current tasks

Main Memory - RAM

RAM – Random Access Memory It’s like your office

Need to get up from your desk to grab items to work on

You usually grab multiple at a time to save roundtrips

Our office

CPU

Your hands2 seconds CPU

Cache“Desk”4 sec.

Main Memory (RAM)“Your office”12 seconds

Disk“Flying to Australia”

8 hours

TAPE – use a cargo ship to go

Growing your office

You always need more Your “office” needs to handle all your

active clients, or they will be unhappy Running out of space in your office is not

acceptable

The Disk – extending the memory

The Solution? Ship some of your least needed binders to

Australia Relatively complex process

need to find the least needed binders need to know how to return them, when they

are needed

Introduction to virtual memory

Processes “see” memory independently, as if it was alone on the system

Each process has freedom to use addresses in the whole “user address space”

Typically – 3 Gb user space, 1 Gb system space (on 32 bit)

Virtual memory mapping

P1

P2

32 bit addressing space

0 gb 1 gb 2 gb 3 gb 4 gb

RAM

RAM split into 4 kb chunks

Reservedvirtualregion

for the system

(kernel)

VM Management

Implemented via per process page table Indicates:

page location (disk/memory) page permissions (read/write/execute) page attributes (ex. copy on write)

Virtual memory PTE table

P1

PTE Table for P1rw – in RAM – 0xFFArw – in RAM – 0xFFB

in RAM – 0xFFC – copy on write w – unallocated

rw – on disk - SWAPrx – on disk - FILE

unallocated

RAM

FILE SWAP

Additional benefits from VM

Protection Features

memory mapped files in memory file system shared memory shared memory – copy on write

Use more then what you have

Concept types of memory

Shared initially exists on disk

file cache(linux), buffers, system cache initially does not exist on disk

anonymous(linux), computed(aix)

Private does not exist on disk special case copy on write

Linux VM Components

direct “user” dependant types of memory Buffers (shared) Cached (shared) Anonymous (private or shared) Hugepages

indirect (system) managed areas Slab – kernel structures PageTables

VM areas with Oracle

Cached

SLAB

Pagetables

System User

Buffers

Mapped

IPC Memory (SGA)

Anonymous (PGA,PLSQL arrays)

Monitoring

Monitoring Memory

with Oracle in mind

TOP

top most commonly used tool most confused interpretation

top – sample outputtop - 22:03:11 up 3:19, 2 users, load average: 2.98, 1.22, 0.52Tasks: 89 total, 1 running, 88 sleeping, 0 stopped, 0 zombieCpu0 : 0.7% us, 0.8% sy, 0.0% ni, 0.3% id, 98.0% wa, 0.2% hi, 0.0% siCpu1 : 0.0% us, 0.8% sy, 0.0% ni, 97.6% id, 1.4% wa, 0.2% hi, 0.0% siCpu2 : 0.0% us, 0.2% sy, 0.0% ni, 99.7% id, 0.2% wa, 0.0% hi, 0.0% siCpu3 : 0.2% us, 0.2% sy, 0.0% ni, 33.6% id, 66.1% wa, 0.0% hi, 0.0% siMem: 8310308k total, 8049068k used, 261240k free, 36620k buffersSwap: 7823644k total, 572k used, 7823072k free, 3395900k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND

8494 oracle 16 0 1662m 1.6g 1.5g D 2.0 19.8 0:03.15 oracletest (LOCAL=YES) 4796 oracle 16 0 1626m 1.5g 1.5g S 1.0 19.5 0:03.91 ora_dbw1_test

4794 oracle 15 0 1626m 1.5g 1.5g S 0.7 19.5 0:12.23 ora_dbw0_test

4798 oracle 16 0 1626m 1.5g 1.5g S 0.7 19.5 0:03.97 ora_dbw2_test

4800 oracle 16 0 1626m 1.5g 1.5g S 0.7 19.5 0:04.09 ora_dbw3_test

1 root 16 0 2384 600 512 S 0.0 0.0 0:00.86 init [3]

2 root RT 0 0 0 0 S 0.0 0.0 0:00.00 [migration/0]

3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 [ksoftirqd/0]

Top – data comes from

/proc/<pid>/statuscat /proc/10450/statusName: oracleState: S (sleeping)SleepAVG: 98%Tgid: 10450Pid: 10450PPid: 1TracerPid: 0Uid: 503 503 503 503Gid: 503 503 503 503FDSize: 256Groups: 503 603

VmSize: 83424 kBVmLck: 0 kBVmRSS: 1484204 kBVmData: 1612 kBVmStk: 124 kBVmExe: 52720 kBVmLib: 8420 kB…

top – additional columns

top can have additional columns swap file usage

computed code data

THEY ARE ALL WRONG

vmstatvmstat 2procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 3631424 11096 120204 0 0 35 31 255 20 0 0 99 0 0 0 0 3631488 11096 120204 0 0 0 0 1014 18 0 0 100 0 0 0 0 3631488 11096 120204 0 0 0 0 1012 16 0 0 100 0

r – run queue – how many processes currently waiting for or running on the CPU

b – how many processes waiting, usually waiting on IO swpd – swap memory usage free – free memory cache – file system cache

vmstat contvmstat 2procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 3631424 11096 120204 0 0 35 31 255 20 0 0 99 0 0 0 0 3631488 11096 120204 0 0 0 0 1014 18 0 0 100 0 0 0 0 3631488 11096 120204 0 0 0 0 1012 16 0 0 100 0

si/so – swap in / out – in Kb/sec bi/bo – bytes in / out – in Kb/sec cs – context switches us/sy/id/wa – user/system/idle/wait time for CPUs

/proc/meminfo

cat /proc/meminfoMemTotal: 8310308 kBMemFree: 93448 kBBuffers: 132036 kBCached: 3413324 kBSwapCached: 0 kBActive: 1658252 kBInactive: 1942032 kBHighTotal: 7470528 kBHighFree: 8768 kBLowTotal: 839780 kBLowFree: 84680 kB

SwapTotal: 7823644 kBSwapFree: 7823072 kBDirty: 100 kBWriteback: 0 kBMapped: 82500 kBSlab: 92028 kBCommitted_AS: 490700 kBPageTables: 3952 kBVmallocTotal: 106488 kBVmallocUsed: 5964 kBVmallocChunk: 99900 kBHugePages_Total: 2200HugePages_Free: 1088Hugepagesize: 2048 kB

/proc/meminfo – 64 bit

cat /proc/meminfoMemTotal: 8165032 kBMemFree: 106428 kBBuffers: 219484 kBCached: 2864760 kBSwapCached: 69256 kBActive: 1508428 kBInactive: 1915392 kBHighTotal: 0 kBHighFree: 0 kBLowTotal: 8165032 kBLowFree: 106428 kB

SwapTotal: 4816888 kBSwapFree: 4192148 kBDirty: 252 kBWriteback: 0 kBMapped: 1350480 kBSlab: 461584 kBCommitLimit: 6851404 kBCommitted_AS: 4959776 kBPageTables: 46668 kBVmallocTotal: 536870911 kBVmallocUsed: 2992 kBVmallocChunk: 536867847 kBHugePages_Total: 2000HugePages_Free: 128Hugepagesize: 2048 kB

MemTotal

Total memory visible by the OS If it’s not what you’ve put in the machine,

probably you have a bad SIM/DIMM

MemFree

Memory that is currently un-occupied and available to use immediately

Not the maximum amount of memory available at the moment

Controlled by (Linux RH4) /proc/sys/vm/min_free_kbytes

MemFree – example

grep MemFree /proc/meminfoMemFree: 26568 kBecho 900000 > /proc/sys/vm/min_free_kbytesgrep MemFree /proc/meminfo MemFree: 210056 kB

Buffers

Cache of raw disk blocks Usually occupied with ext3 metadata

Mostly ext3 pointers (extent management) Not the cache of actual user data

In older kernels, was controllable

Cached

File system cache If direct IO is not used for datafiles – will have your

datafiles cached Binary (for execution) memory

includes the “oracle” binary caching all the libraries caching

Does not mean “occupied” – usually can be released immediately

The Oracle SGA – when not using hugepages

Cached – example part 1

[root@ ~]# cat /proc/meminfo …MemFree: 8232512 kBBuffers: 9328 kBCached: 28372 kB…du -smc indx01_*1714 indx01_01.dbf1761 indx01_02.dbf1722 indx01_03.dbf5197 total…cat indx01_* > /dev/null

Cached – example part 2

[root@ ~]# vmstat 2procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 8093888 10808 163392 0 0 0 0 1012 17 0 0 100 0 0 0 0 8093952 10808 163392 0 0 0 0 1012 16 0 0 100 0 0 1 0 7956736 10948 300272 0 0 68602 0 1567 1126 0 2 76 22 0 1 0 7808576 11092 448068 0 0 73992 80 1623 1210 0 2 75 23… 0 1 0 2847616 16104 5397616 0 0 65792 0 1542 1076 0 2 75 23 0 0 0 2766272 16180 5479180 0 0 40698 0 1341 675 0 1 85 14 0 0 0 2766208 16192 5479168 0 0 0 114 1033 22 0 0 100 0cat /proc/meminfo …MemFree: 2766464 kBBuffers: 16192 kBCached: 5479168 kB…

Cached – example #2 part 1cat indx01_* >newfilevmstat 2procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 2765312 17044 5479356 0 0 0 0 1012 17 0 0 100 0 0 3 0 2405376 17428 5833612 0 0 16 36866 1324 144 1 18 76 6 0 2 0 2143616 17688 6091532 0 0 4 111748 2000 213 0 16 50 34… 0 1 0 16832 6784 8198556 0 0 8556 26684 1942 1267 0 2 74 24 1 1 0 16832 6856 8198744 0 0 12518 20720 2130 1767 0 3 74 23…cat /proc/meminfo …MemFree: 16768 kBBuffers: 2192 kBCached: 8196908 kB…Dirty: 277468 kBWriteback: 0 kB…

Cached – example #2 part 2cat /proc/meminfo …MemFree: 20672 kBBuffers: 3300 kBCached: 8191900 kB…Dirty: 0 kBWriteback: 0 kB…rm newfileprocs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 23296 3380 8189480 0 0 0 28 1015 18 0 0 100 0 0 1 0 3257472 3948 4996372 0 0 284 0 1084 160 0 14 78 8 0 1 0 3255552 5828 4996572 0 0 940 0 1247 485 0 1 75 24 0 1 0 3253696 7616 4996344 0 0 884 96 1237 470 0 2 75 23 0 0 0 3253440 7988 4996492 0 0 186 0 1061 112 0 0 95 4 0 0 0 3253440 7988 4996492 0 0 0 0 1012 14 0 0 100 0

Swap

SwapTotal SwapFree SwapCached

written to swap, but still in memory applies only to anonymous memory OS will anticipate memory needs, and pre-swap

inactive data, but keep it in memory Actual swapping (memory that will need to be

read from disk) = SwapTotal - SwapFree - SwapCached

Active/Inactive

Active – recently used memory Includes all types of memory

(cached, buffers, anonymous) OS will try to keep it in RAM

Inactive – memory that will be first reused “free” memory

Can be used to gauge the “working set”

High/Low Total/Free

32 bit limitations, no high memory on 64 bit

Some kernel structures cannot be allocated in “high memory”

Used to be a problem in older kernels, newer kernels protect low memory

Dirty & Writeback

Dirty – cache/buffers memory that requires to be written to disk thresholds can be adjusted

Writeback – memory actively been written to disk Can reach high values with async writes with

large queue

Committed_AS & Mapped Committed_AS

Total memory requested on the system Not used, just requested If every process in the system is to touch and use

the memory it has requested, this is how much would be used

Mapped memory used for in-memory mapped files all anonymous memory includes committed & touched memory

Committed_AS - example

cat grab.c main() {void *p;p=malloc(1073741824);sleep(60);}

cat /proc/meminfo ...MemFree: 3230592 kB...Committed_AS: 49972 kB

./grabcat /proc/meminfo ...MemFree: 3230464 kB...Committed_AS: 1098808 kB

Slab

Slab – “in-kernel data structures cache” similar to Oracle’s “shared_pool” designed to prevent memory fragmentation detailed monitoring:

/proc/slabinfoslabtop

Basically “system space”

slabtop – ordered by cache size

Active / Total Objects (% used) : 88874 / 139343 (63.8%) Active / Total Slabs (% used) : 5839 / 5846 (99.9%) Active / Total Caches (% used) : 90 / 132 (68.2%) Active / Total Size (% used) : 17286.03K / 23311.27K (74.2%) Minimum / Average / Maximum Object : 0.01K / 0.17K / 128.00K

OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 32382 24900 76% 0.27K 2313 14 9252K radix_tree_node 56925 40013 70% 0.05K 759 75 3036K buffer_head 364 363 99% 4.00K 364 1 1456K size-4096 2485 2471 99% 0.54K 355 7 1420K ext3_inode_cache 2376 413 17% 0.50K 297 8 1188K size-512 256 256 100% 3.00K 128 2 1024K biovec-(256) 4576 4481 97% 0.15K 176 26 704K dentry_cache 10248 4548 44% 0.06K 168 61 672K size-64 4340 1215 27% 0.12K 140 31 560K size-128 1980 316 15% 0.25K 132 15 528K size-256…

HugePages

2Mb pages organized in a separate memory pool locked in memory available only to shared memory requests pre-allocated via kernel parameter

Shared memory mapping

P1

P2

32 bit addressing space

0 gb 1 gb 2 gb 3 gb 4 gb

RAM Reservedvirtualregion

for the system

(kernel)

Shared memory mapping (huge)

P1

P2

32 bit addressing space

0 gb 1 gb 2 gb 3 gb 4 gb

RAM

HugePagesPre-AllocatedMemory pool

Locked in RAM

VLM – 32 bit workarround

32 bit adress space is 4 Gb 32 bit systems with PAE (Intel)

up to 64 Gb of ram Memory filesystem

opens a file in /dev/shm for buffer cache shared pool still in Shared Memory

Beware of small Oracle block size

VLM – using 3gb+ on 32 bit

P1

P2

32 bit addressing space

0 gb 1 gb 2 gb 3 gb 4 gb

RAM

/dev/shm/ora_

ramfsmmap region

USE_INDIRECT_BUFFERS

RedHat/SUSE shmfs – needs size tmpfs – does not need size ramfs – does not need size + Locked

none can use HugePages shared pool can still use HugePages double-memory access due to mapping

DirectIO

Direct IO (O_DIRECT) – bypasses file system cache and access the files directly

DB activity does not pollute OS cache DB activity does not compete with

PGA/PLSQL memory

PageTables Memory for per-process page tables

B-Tree like structure – this number shows leaf blocks space

Memory to manage memory One entry of ~4 bytes per process, per used 4kb of

memory In Oracle’s case, assuming an SGA of 2gb

524’288 pages * 8 bytes = 4 Mb per process 1000 sessions = 4 Gb of memory, to manage

2gb of SGA

Case studies

PageTables using a lot of ram

PageTables – bad example

Config: 1.7 Gb sga (max on 32 bit without VLM) 1400 Mb in db_cache_size table sized to fit exactly in cache

Start 100 sessions, that full scan the table (cached) in order to touch the memory and allocate the PTEs Sessions will wait via dbms_lock.allocate to be released

Show before and after PageTables usage

PageTables – bad example cont. Before starting the sessions (db is UP)cat /proc/meminfo…MemFree: 1070472 kB…Committed_AS: 1881544 kBPageTables: 4932 kB…

After sessions have finished touching the memorycat /proc/meminfo…MemFree: 473496 kB…Committed_AS: 4708552 kBPageTables: 295068 kB

HugePages & Oracle

Locks SGA in memory no part of the SGA will ever be swapped out,

or even considered for swapping Reduces the number of PTE entries

Assuming 2 Gb SGA 1’000 PTEs * 8 bytes = 8 Kb per process

1000 sessions = 4 Mb of memory, a 512 fold reduction

HugePages & Performance Releases more memory for PGA or more

db_cache Guarantees that SGA will always be in

memory Improves TLB hit ratio

TLB is a CPU level cache of virtual to physical memory mappings, improving performance

8% improvement in a memory only TPC test not including the fact there is more memory

available

HugePages & 100 sessions The test from a few slides before Before starting 100 sessions (db up)cat /proc/meminfo …Committed_AS: 332264 kBPageTables: 3056 kB…

After…Committed_AS: 3124640 kBPageTables: 23100 kB…

No hugepages

Cached

SLAB

Pagetables

System User

Buffers

Mapped

IPC Memory (SGA)

Anonymous (PGA,PLSQL arrays)

With HugePages

Cached

SLAB

Pagetables

System User

Buffers

Mapped

IPC Memory (SGA)

Hugepages

Anonymous (PGA,PLSQL arrays)

HugePages – on Red Hat

what you need to setup RH4 /proc/sys/vm/nr_hugepages /proc/sys/vm/hugetlb_shm_group /etc/security/limits.conf

Case studies

Where is my free memory going?

Freshly bootedvmstat 2 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 7725800 13036 497864 0 0 0 16 1013 25 0 0 100 0 0 1 0 7663272 13144 556516 0 0 14806 70 1164 393 2 2 80 16 0 1 0 7513128 13252 706168 0 0 37494 0 1318 631 2 3 75 20 0 1 0 7310824 13408 908032 0 0 50502 64 1429 862 3 4 75 18... 0 1 0 5503208 14724 2709556 0 0 59144 16 1493 987 3 4 75 18 1 0 0 5263080 14856 2948884 0 0 59838 128 1518 995 3 5 75 18 0 0 0 5111272 14944 3106096 0 0 39344 6 1332 663 2 5 82 11 0 0 0 5111272 14944 3106096 0 0 0 16 1013 26 0 0 100 0 0 0 0 5111144 14960 3106080 0 0 0 30 1016 36 0 0 100 0

Reading ~1.2 Gb of data, free memory drops twice as much file system cache oracle SGA been touched

Freshly booted – hugepagesvmstat 2 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 3436280 14236 286324 0 0 0 56 1027 54 0 0 100 0 0 1 0 3395192 14336 323924 0 0 18902 24 1193 447 2 1 81 16 0 1 0 3303928 14480 415040 0 0 45572 48 1387 775 3 1 75 21… 0 1 0 2566776 15560 1150020 0 0 49228 6 1416 828 3 1 75 20 0 1 0 2452152 15720 1264260 0 0 57230 18 1492 977 3 1 75 20

Reading 1.2 Gb of data, free memory drops with same amount file system cache consuming memory

Freshly booted – with directIOvmstat 2 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 0 0 0 3436280 14236 286324 0 0 0 56 1027 54 0 0 100 0 0 1 0 3395192 14336 323924 0 0 18902 24 1193 447 2 1 81 16 0 1 0 3303928 14480 415040 0 0 45572 48 1387 775 3 1 75 21… 0 1 0 2566776 15560 1150020 0 0 49228 6 1416 828 3 1 75 20 0 1 0 2452152 15720 1264260 0 0 57230 18 1492 977 3 1 75 20

1.2 Gb of data – 1.2 Gb drop in free memory NO CHANGE

DIRECT_IO Bugs

bug 3186847 filesystemio_options=directio is ignored on linux fixed in 9.2.0.6

Note: 297521.1 bug 2448994 introduced - O_DIRECT flag was not

passed to the open() system call fixed in 9.2.0.7

Basically you need 9.2.0.7

Shared memory monitoring

How to see shared memory? ipcs – shows the “IPC” shared memory

If you kill Oracle without freeing up shared memory ipcrm – to remove

ipcs

ipcs------ Shared Memory Segments --------key shmid owner perms bytes nattch status

0x00000000 4915200 oracle 600 2097152 14

0x00000000 4947969 oracle 600 1342177280 14

0x7157be04 4980738 oracle 600 278921216 14

------ Semaphore Arrays --------key semid owner perms nsems 0xb1adfd8c 622592 oracle 640 354

------ Message Queues --------key msqid owner perms used-bytes messages

To remove orphan segments

Identified via “sysresv” or number attached from ipcs or pmap of an oracle pid

Use ipcrm to remove

The End

Thank you,

Questions?

kutrovsky@pythian.comVisit my blog at

http://www.pythian.com/blogs/kutrovsky/

Christo Kutrovsky

The Pythian Group

2007 Aprilhttp://www.pythian.com/