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The Answer to Free Memory, Swap, Oracle and everything

The Answer to Free Memory, Swap, Oracle and everything. A presentation about using memory where it’s needed most. Christo Kutrovsky The Pythian Group 2007 April. Agenda. What is memory How do we get more of it Virtual Memory areas How do we monitor memory usage And make sense of it

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The Answer to Free Memory, Swap, Oracle and everything

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  1. The Answer to Free Memory, Swap, Oracle and everything A presentation about using memory where it’s needed most Christo Kutrovsky The Pythian Group 2007 April

  2. Agenda • What is memory • How do we get more of it • Virtual Memory areas • How do we monitor memory usage • And make sense of it • Oracle examples

  3. 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

  4. Terminology • What is memory • The ability of a computer system to store data

  5. Types of Memory • Short term • RAM (memory) • Long term (“permament”) • Disk, tape (storage)

  6. Types of Memory - physical • CPU Registers • fastest, very limited • CPU Cache (L1/L2/L3) • some latency, LRU maintained • RAM • major latency (relativelly), partially LRU • Disk • do something else while you wait

  7. What is RAM • Faster, temporary storage • A work area • A place where you put your data while you process it

  8. The Many caches CPU Registers2 ns CPU Cache 8 ns 1:4 Main Memory (RAM) 100ns 1:12 CPU Disk – Long term memory 3’000’000 ns 1:30’000 TAPE – even longer

  9. 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

  10. 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

  11. Our office Your hands2 seconds CPU Cache “Desk”4 sec. Main Memory (RAM) “Your office” 12 seconds CPU Disk “Flying to Germany” 8 hours TAPE – use a cargo ship to go

  12. The bad news • You always need more • Running out of space in your office is not acceptable

  13. The Disk – extending the memory • The Solution? • Ship some of your least needed binders to Germany • Relatively complex process • need to find the least needed binders • need to know how to find them, if they are needed

  14. 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)

  15. Virtual memory mapping 32 bit addressing space 0 gb 1 gb 2 gb 3 gb 4 gb P1 P2 Reservedvirtualregion for the system(kernel) RAM RAM split into 4 kb chunks

  16. VM Management • Implemented via per process page table • Indicates: • page location (disk/memory) • page permissions (read/write/execute) • page attributes (ex. copy on write)

  17. Virtual memory PTE table PTE Table for P1 rw – in RAM – 0xFFA rw – in RAM – 0xFFB RAM in RAM – 0xFFC – copy on write w – unallocated rw – on disk - SWAP rx – on disk - FILE unallocated FILE SWAP P1

  18. 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

  19. Concept type of memory • Shared • initially exists on disk • file cache, buffers, system cache • initially does not exist on disk • anonymous, computed • Private • does not exist on disk • special case copy on write

  20. 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

  21. VM areas with Oracle System User SLAB Buffers Mapped Anonymous (PGA,PLSQL arrays) Pagetables Cached IPC Memory (SGA)

  22. Monitoring Monitoring Memory with Oracle in mind

  23. TOP • top • most commonly used tool • most confused interpretation

  24. top – sample output top - 22:03:11 up 3:19, 2 users, load average: 2.98, 1.22, 0.52 Tasks: 89 total, 1 running, 88 sleeping, 0 stopped, 0 zombie Cpu0 : 0.7% us, 0.8% sy, 0.0% ni, 0.3% id, 98.0% wa, 0.2% hi, 0.0% si Cpu1 : 0.0% us, 0.8% sy, 0.0% ni, 97.6% id, 1.4% wa, 0.2% hi, 0.0% si Cpu2 : 0.0% us, 0.2% sy, 0.0% ni, 99.7% id, 0.2% wa, 0.0% hi, 0.0% si Cpu3 : 0.2% us, 0.2% sy, 0.0% ni, 33.6% id, 66.1% wa, 0.0% hi, 0.0% si Mem: 8310308k total, 8049068k used, 261240k free, 36620k buffers Swap: 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]

  25. Top – data comes from /proc/<pid>/status cat /proc/10450/status Name: oracle State: S (sleeping) SleepAVG: 98% Tgid: 10450 Pid: 10450 PPid: 1 TracerPid: 0 Uid: 503 503 503 503 Gid: 503 503 503 503 FDSize: 256 Groups: 503 603 VmSize: 83424 kB VmLck: 0 kB VmRSS: 1484204 kB VmData: 1612 kB VmStk: 124 kB VmExe: 52720 kB VmLib: 8420 kB …

  26. top – additional columns • top can have additional columns • swap file usage • computed • code • data • THEY ARE ALL WRONG

  27. vmstat vmstat 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 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

  28. vmstat cont vmstat 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 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

  29. /proc/meminfo • cat /proc/meminfo MemTotal: 8310308 kB MemFree: 93448 kB Buffers: 132036 kB Cached: 3413324 kB SwapCached: 0 kB Active: 1658252 kB Inactive: 1942032 kB HighTotal: 7470528 kB HighFree: 8768 kB LowTotal: 839780 kB LowFree: 84680 kB SwapTotal: 7823644 kB SwapFree: 7823072 kB Dirty: 100 kB Writeback: 0 kB Mapped: 82500 kB Slab: 92028 kB Committed_AS: 490700 kB PageTables: 3952 kB VmallocTotal: 106488 kB VmallocUsed: 5964 kB VmallocChunk: 99900 kB HugePages_Total: 2200 HugePages_Free: 1088 Hugepagesize: 2048 kB

  30. /proc/meminfo – 64 bit SwapTotal: 4816888 kB SwapFree: 4192148 kB Dirty: 252 kB Writeback: 0 kB Mapped: 1350480 kB Slab: 461584 kB CommitLimit: 6851404 kB Committed_AS: 4959776 kB PageTables: 46668 kB VmallocTotal: 536870911 kB VmallocUsed: 2992 kB VmallocChunk: 536867847 kB HugePages_Total: 2000 HugePages_Free: 128 Hugepagesize: 2048 kB • cat /proc/meminfo MemTotal: 8165032 kB MemFree: 106428 kB Buffers: 219484 kB Cached: 2864760 kB SwapCached: 69256 kB Active: 1508428 kB Inactive: 1915392 kB HighTotal: 0 kB HighFree: 0 kB LowTotal: 8165032 kB LowFree: 106428 kB

  31. 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

  32. 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

  33. MemFree – example grep MemFree /proc/meminfo MemFree: 26568 kB echo 900000 > /proc/sys/vm/min_free_kbytes grep MemFree /proc/meminfo MemFree: 210056 kB

  34. Buffers • Cache of raw disk blocks • Usually occupied with ext3 data pointers (extent management data) • Not the cache of actual user data • In older kernels, was controllable

  35. Cached • File system cache • If direct IO is not used for datafiles – will have your datafiles cached as much as possible • 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

  36. Cached – example part 1 [root@~]# cat /proc/meminfo … MemFree: 8232512 kB Buffers: 9328 kB Cached: 28372 kB … du -smc indx01_* 1714 indx01_01.dbf 1761 indx01_02.dbf 1722 indx01_03.dbf 5197 total … cat indx01_* > /dev/null

  37. Cached – example part 2 [root@~]#vmstat 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 8093888 10808 163392 0 0 0 0 1012 17 0 0 100 0 0 0 0 809395210808163392 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 780857611092448068 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 0 cat /proc/meminfo … MemFree: 2766464 kB Buffers: 16192 kB Cached: 5479168 kB …

  38. Cached – example #2 part 1 cat indx01_* >newfile vmstat 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 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 kB Buffers: 2192 kB Cached: 8196908 kB … Dirty: 277468 kB Writeback: 0 kB …

  39. Cached – example #2 part 2 cat /proc/meminfo … MemFree: 20672 kB Buffers: 3300 kB Cached: 8191900 kB … Dirty: 0 kB Writeback: 0 kB … rm newfile 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 2329633808189480 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

  40. 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

  41. Active/Inactive • Active – recently used memory • Includes all types of memory (cached, buffers, anonymous) • OS will try to keep it in memory • Inactive – memory that will be first reused • “free” memory • Can be used to gauge overall memory usage

  42. 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

  43. Dirty & Writeback • Dirty – cache/buffers memory that requires to be written to disk • cannot be anonymous memory • Writeback – memory actively been written to disk • Can reach high values with async writes with large queue

  44. 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

  45. Committed_AS - example cat grab.c main() {void *p; p=malloc(1073741824); sleep(60);} cat /proc/meminfo ... MemFree: 3230592 kB ... Committed_AS: 49972 kB ./grab cat /proc/meminfo ... MemFree: 3230464 kB ... Committed_AS: 1098808 kB

  46. 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”

  47. 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 …

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

  49. Shared memory mapping 32 bit addressing space 0 gb 1 gb 2 gb 3 gb 4 gb P1 P2 Reservedvirtualregion for the system(kernel) RAM

  50. Shared memory mapping (huge) 32 bit addressing space 0 gb 1 gb 2 gb 3 gb 4 gb P1 P2 RAM HugePagesPre-AllocatedMemory pool Locked in RAM

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