Error Accessing Shared Memory Semaphores Using Oracle Directly

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Oracle Semaphores Linux

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Oracle Database Semaphore

table or view does not exist More You are hereHome » Blogs » Nidhi Jain's blog Understanding Shared Memory and Semaphores Submitted by Nidhi Jain on Mon, 2003-12-15 13:03 articles:Operating Systemsby Nidhi Jain Shared memory and oracle semaphore lock semaphores are two important resources for an Oracle instance on Unix. An instance cannot start if it is unable to allocate what it needs. DEFINATIONS Shared memory is exactly that - a memory region that can shared between different processes. Oracle uses shared memory for implementing the SGA, which needs to be visible to all database sessions. Semaphores can be thought of as flags (hence their name, semaphores). They are either on or what is semaphore in oracle dba off. A process can turn on the flag or turn it off. If the flag is already on, processes who try to turn on the flag will sleep until the flag is off. Upon awakening, the process will reattempt to turn the flag on, possibly suceeding or possibly sleeping again. Such behaviour allows semaphores to be used in implementing a post-wait driver - a system where processes can wait for events (i.e. wait on turning on a semphore) and post events (i.e. turning of a semaphore). This mechanism is used by Oracle to maintain concurrency control over the SGA, since it is writeable by all processes attached. ALLOCATION IN SIMPLE TERMS Shared memory required by the Oracle Instance : On instance startup, the first things that the instance does is: -Read the "init.ora" -Start the background processes -Allocate the shared memory and semphores required The size of the SGA will be calculated from various "init.ora" parameters. This will be the amount of shared memory required. The SGA is broken into 4 sections - the fixed portion, which is constant in size, the variable portion, which varies in size depending on "init.ora" parameters, the redo block buffer, which has its size controlled by log_buffers, and the db block buffer, which has its size controlled by db_block_buffers. The size o

each another. Since each process has its own address space and unique user space, how does the process communicate each other? The answer is Kernel, the heart of the Linux operating system that has access to the whole memory.

Oracle 11g Linux Semaphores

So we can request the kernel to allocate the space which can be used to semmns communicate between processes. The process can also communicate by having a file accessible to both the processes. Processes can open, and read/write

Semmsl Kernel Parameter

the file, which requires lot of I/O operation that consumes time. Different Types of IPCS There are various IPC's which allows a process to communicate with another processes, either in the same computer or different computer in the http://www.orafaq.com/node/8 same network. Pipes - Provides a way for processes to communicate with each another by exchanging messages. Named pipes provide a way for processes running on different computer systems to communicate over the network. Shared Memory - Processes can exchange values in the shared memory. One process will create a portion of memory which other process can access. Message Queue - It is a structured and ordered list of memory segments where processes store or http://www.thegeekstuff.com/2010/08/ipcs-command-examples retrieve data. Semaphores - Provides a synchronizing mechanism for processes that are accessing the same resource. No data is passed with a semaphore; it simply coordinates access to shared resources. 10 IPCS Command Example ipcs is a UNIX / Linux command, which is used to list the information about the inter-process communication ipcs command provides a report on System V IPCS (Message queue, Semaphore, and Shared memory). IPCS Example 1: List all the IPC facility ipcs command with -a option lists all the IPC facilities which has read access for the current process. It provides details about message queue, semaphore and shared memory. # ipcs -a ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0xc616cc44 1056800768 oracle 660 4096 0 0x0103f577 323158020 root 664 966 1 0x0000270f 325713925 root 666 1 2 ------ Semaphore Arrays -------- key semid owner perms nsems 0x0103eefd 0 root 664 1 0x0103eefe 32769 root 664 1 0x4b0d4514 1094844418 oracle 660 204 ------ Message Queues -------- key msqid owner perms used-bytes messages 0x000005a4 32768 root 644 0 0 All the IPC facility has unique key and identifier, which is used to identify an IPC facility. IPCS Example 2: List all the Message Queue ipcs with option -q, lists only message queues for which the current process has read access. $ ipcs -q ------ Message Q

problems with your database after following the troubleshooting recommendations in this chapter, contact TimesTen technical support. Unable to start https://docs.oracle.com/cd/E11882_01/timesten.112/e21636/datastore_trouble.htm or stop TimesTen daemon No response from TimesTen daemon or https://docs.oracle.com/cd/E13203_01/tuxedo/tux64/errman/ltmsg01.htm subdaemon Unable to create shared segment Application unable to connect to database in direct mode Troubleshooting Client/Server problems Application connects or disconnects are slow Application is disconnected unexpectedly Application is slow Application unresponsive, appears hung Application unable to find previously created objects Troubleshooting semaphore in OCI and Pro*C/C++ applications Running out of a resource Duplicate results from a SELECT statement Cannot attach PL/SQL shared memory Unable to start or stop TimesTen daemon This section describes what to check if you cannot start or stop the TimesTen main daemon. Possible cause What to do Privilege is incorrect. You need the semaphore in oracle ADMIN privilege to start or stop the TimesTen daemon. Ensure that you are using the ttDaemonAdmin utility to start the daemon. The output from ttDaemonAdmin shows whether you have the correct privilege. Another process is using the TimesTen daemon port. Use the ttVersion utility to verify what port number the TimesTen daemon is expected to use. Use an operating system command like netstat to check whether another process is listening on the port. If there is a conflict, either change the port number used by the other process or use ttmodinstall to change the port used by TimesTen. TimesTen daemon is already running. Ensure that you are using the ttDaemonAdmin utility to start the daemon. The output from ttDaemonAdmin shows whether the daemon is already running. There are other problems. Inspect the user error log produced by the daemon. See "Using the logs generated by the TimesTen daemon". No response from TimesTen daemon or subdaemon The following sections descr

system call returned the errno indicated in the message. ACTION Contact your TUXEDO System Technical Support. 301 ERROR: funcname: cannot free space DESCRIPTION An attempt to free space that was allocated in the VTOC has failed because there are no more available VTOC map entries. ACTION Contact your TUXEDO System Technical Support. 302 ERROR: funcname: bad table name specified DESCRIPTION An error occurred while either creating a new table entry or accessing an existing table entry in the VTOC. If the error occurred while attempting to create a table, either the table name already exists, or the name has a length of 0 or is greater than the allowable table name size (GP_LOGICAL_NAME). If the error occurred while attempting to access an existing table, either the name doesn't exist, or the name has a length of 0 or is greater than the allowable table name size. ACTION Contact your TUXEDO System Technical Support. 303 ERROR: funcname: invalid arguments or request to function DESCRIPTION An error occurred because the indicated function was invoked with invalid arguments. ACTION Contact your TUXEDO System Technical Support. 304 ERROR: funcname: bad device name or index specified DESCRIPTION An attempt to access a device has failed because the name used was either of length 0 or was longer than the allowable length of GP_LOGICAL_NAME . ACTION Contact your TUXEDO System Technical Support. 305 ERROR: funcname: attempt to create overlapping devices DESCRIPTION An error has occurred because of an overlap in devices. An overlap occurs if the new device begins before the old device ends and the new device ends after the old device begins. ACTION Contact your TUXEDO System Technical Support. 306 ERROR: funcname: no entry remains to create device or table or open table DESCRIPTION An attempt to either create a device or table, or open a table has failed because there are no more available slots in the device list. ACTION Contact your TUXEDO System Technical Support. 308 ERROR: funcname: bad device type (not character special or regular) DESCRIPTION An attempt to create a disk entry has failed because an invalid device type has been specified. The only two available device types are character special and regular