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Cannot get shared memory segment Error When Starting Tibero in Linux Environment

Document Type | Troubleshooting 

Category | Administration

Applicable Product Versions | 5SP1FS01, 5SP1FS02, 5SP1FS03, 5SP1FS04, 5SP1FS06, 6FS01, 6FS02, 6FS03, 6FS04, 6FS05, 6FS06, 6FS07, 6FS07PS, 7FS01, 7FS02, 7FS02PS

Document Number | TADTS009

 

Issue

When starting Tibero, the error "Cannot get shared memory segment" occurs, and it does not start normally.
$ tbboot 
 shmget failed.: No space left on device
***************************************************************************
* Cannot get shared memory segment:
* SHM_KEY = 0x780d5c27, size = 3221225472, errno=28 (No space left on device)
***************************************************************************


 

Cause

In Linux, files stored on disk are loaded into the memory area called the file cache before use, compensating for the relatively slower performance compared to disk access.
 
Also, even after using the files, the data is not immediately released but kept in the file cache considering the possibility of future reuse, reducing the overhead of reloading from the slow disk.
 
If available memory becomes insufficient due to unreleased file cache, the "Cannot get shared memory segment" error may occur when starting Tibero, causing startup failure.
$ tbboot 
 shmget failed.: No space left on device
***************************************************************************
* Cannot get shared memory segment:
* SHM_KEY = 0x780d5c27, size = 3221225472, errno=28 (No space left on device)
***************************************************************************

You can check the usage of the file cache area (buffers/cache) and the actual free memory of the system using the free command.
# free -mt 
              total        used        free      shared  buff/cache   available
Mem:          18046        4606        2844        9834       10596        3369
Swap:         32763         724       32039
Total:        50810        5330       34884


 

Solutions

Use the vm.drop_caches kernel parameter to release memory in the file cache area, securing free memory, and then try starting Tibero again.
 
Below is an example of application.
# sync
* Reflects data changed only in memory to disk before clearing the file cache.

# sysctl -w vm.drop_caches=3
vm.drop_caches = 3
* Releases occupied file cache memory


# free -mt 
              total        used        free      shared  buff/cache   available
Mem:          18046        4500        3861        9221        9684        4087
Swap:         32763         724       32039
Total:        50810        5224       35901
* Secured free memory by releasing file cache


$ tbboot 
Listener port = 8629
Tibero 7
TmaxTibero Corporation Copyright (c) 2020-. All rights reserved.
Tibero instance started up (NORMAL mode).
* Startup successful

Note

The vm.drop_caches kernel parameter applies only at the time of setting and is not a persistent setting.
Using this parameter allows selective release of items stored in the file cache.

Below are examples of settings.

1. Release pagecache
# sysctl -w vm.drop_caches = 1

2. Release dentries, inodes 
# sysctl -w vm.drop_caches = 2

3. Release pagecache, dentries, inodes
# sysctl -w vm.drop_caches = 3

 

 

 

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