Oracle study--ipcs Manage shared memory

Oracle study--ipcs Manage shared memory

U shared memory, semaphore, queue information management under Nix/linux

Under Unix/linux, there are often problems caused by shared memory, semaphores, queues, and other shared information that are not cleaned up cleanly.

The command to view memory for shared information is: IPCS [-m|-s|-q].

Shared memory, semaphores, queue information are listed by default

-M list shared memory

-S lists shared semaphores

-Q list shared queues

The Purge command is: IPCRM [-m|-s|-q] ID.

- M Delete Shared memory

-S Delete shared semaphore

- Q Delete a Shared Queue .

Case Analysis:

[[email protected]_as02 ~]$ ipcs -a------ Shared Memory Segments ----- ---key        shmid      owner       perms      bytes       nattch     status     0x30024289 32768       futures   777         528384     1                        0xca2fd414 491521      oracle    640        1730150400  16                     ------ semaphore Arrays --------key        semid       owner      perms      nsems      0x00028009 0          futures    666        1          0x0002800c 32769      futures   666         1         0x30024003  262146     futures   777         3         0x3002428a 294915      futures   777        2          0x3002428b 327684     futures   777         2         0x3002428c 360453      futures   777        2          0x3002428d 393222     futures    777        2          0x3002428e 425991     futures   777         2         0x52dff7d0 3964936     oracle    640        151        0x52dff7d1 3997705    oracle     640        151       0x52dff7d2 4030474     oracle    640        151        0x52dff7d3 4063243    oracle    640         151       0x52dff7d4  4096012    oracle    640         151        ------ Message Queues --------Key         msqid      owner       perms      used-bytes   messages

Shared memory segments can sometimes not be deleted immediately, and all processes that use this memory segment are released when the detach command is sent to the OS, considering the amount of semaphores used by the removal process to help free up shared memory segments

Related knowledge: Signal volume, resource release, IPCS, Ipcrm

Semaphores , also known as semaphores, are used to coordinate differentProcessof data Objects, and the most important application is shared memory mode.Processcommunication between the two. Essentially, a semaphore is a counter that is used to record access to a resource (such as shared memory), and shared memory is run on the same machine .ProcessThe fastest way to communicate, because the data does not need to be in a differentProcessreplication between the two. Usually by aProcessCreate a piece of shared memory area, the restProcessRead and write to this memory area. In theLinuxsystem under, the common way is through the SHMXXX function family to realize the use of shared memory for storage. such as Shmget, similar to the malloc function

IPCS can be used to display the usage of shared memory segments, semaphore sets, message queues, and so on in the current Linux system.

command example: Ipcs-a or IPC Displays the usage of shared memory segments, semaphore sets, message queues in the current system, IPCS-M displays the usage of shared memory segments, Ipcs-s displays the usage of the semaphore set, and IPCS-Q displays the usage of the message queue;

IPCRM can be used to delete corresponding shared memory segments, semaphores, message queues;

command example: Ipcrm-s semid Delete the corresponding semaphore set ipcrm-m shmid Delete the corresponding shared memory segment Ipcrm-q msqid Delete the corresponding message queue Ipcrm itself can only implement the deletion of a single resource, using the following command to achieve bulk deletion: 1.ipcs-s |grep username |cut-d ""-f2|xargs-n1 Ipcrm-s2.ipcs-s|awk '/username/{print $} ' |xargs-n1 Ipcrm-s3.ipcs-s|awk '/user name/{system ("I Pcrm-s "$"} ' 4.for I in echo ' Ipcs|grep user name |cut-d "-F2"; Do ipcrm-s $i; Done

More in-depth understanding:

oracle  memory Segment parameter setting:[[email protected] ~]# sysctl -pnet.ipv4.ip_forward =  0net.ipv4.conf.default.rp_filter = 1net.ipv4.conf.default.accept_source_route =  0kernel.sysrq = 0kernel.core_uses_pid = 1net.ipv4.tcp_syncookies = 1error:  "Net.bridge.bridge-nf-call-ip6tables"  is an unknown keyerror:  " Net.bridge.bridge-nf-call-iptables " is an unknown keyerror: " Net.bridge.bridge-nf-call-arptables " is an unknown keyfs.aio-max-nr =  1048576fs.file-max = 6815744kernel.shmall = 2097152kernel.shmmax =  536870912kernel.shmmni = 4096kernel.sem = 250 32000 100 128net.ipv4.ip_ local_port_range = 9000 65500net.core.rmem_default = 262144net.core.rmem_max =  4194304net.core.wmem_default = 262144net.core.wmem_max = 1048586

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Oracle study--ipcs Manage shared memory