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GPDB startup/initilization failed with "could not create semaphores: No space left on device"


During creation of new database cluster with "gpinitsystem" utility or during GPDB restart , the database could not start some of the segments. A sample log on gpstart failure states .

20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-dumping success segments: []
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-----------------------------------------------------
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:2 FAILED host:'sdw5' datadir:'/data1/njonna/gp4300/gpdb_p1/gp0' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:3 FAILED host:'sdw5' datadir:'/data2/njonna/gp4300/gpdb_p2/gp1' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:4 FAILED host:'sdw6' datadir:'/data1/njonna/gp4300/gpdb_p1/gp2' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:5 FAILED host:'sdw6' datadir:'/data2/njonna/gp4300/gpdb_p2/gp3' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:9 FAILED host:'sdw8' datadir:'/data2/njonna/gp4300/gpdb_p2/gp7' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:8 FAILED host:'sdw8' datadir:'/data1/njonna/gp4300/gpdb_p1/gp6' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:6 FAILED host:'sdw7' datadir:'/data1/njonna/gp4300/gpdb_p1/gp4' with reason:
20140205:23:00:05:027234 gpstart:mdw:gpadmin-[INFO]:-DBID:7 FAILED host:'sdw7' datadir:'/data2/njonna/gp4300/gpdb_p2/gp5' with reason:

and on checking the segment log

eg: ssh sdw1
      less /data1/primary/gpdb_p1/gpseg1/pg_log/gpdb-2014-02-05_000000.csv
      less /data1/primary/gpdb_p1/gpseg1/pg_log/startup.log

to understand the encountering for the startup failure, you will witness

2014-02-05 23:00:58.735743 CET,,,p5575,th-41367808,,,,0,,,seg-1,,,,,"FATAL","XX000","could not create semaphores: No space left on device (pg_sema.c:132)","Failed system call was semget(50002001, 17, 03600).",".
It occurs when either the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number of semaphores (SEMMNS), would be exceeded.  You need to raise the respective kernel parameter.  Alternatively, reduce PostgreSQL's consumption of semaphores by reducing its max_connections parameter (currently 250).
The PostgreSQL documentation contains more information about configuring your system for PostgreSQL.",,,,,,"InternalIpcSemaphoreCreate","pg_sema.c",132,1    0xa739de postgres errstart + 0x4ee
2    0x85c6a8 postgres PGSemaphoreCreateInitVal + 0x328
3    0x8e8635 postgres InitProcGlobal + 0x3a5
4    0x8d745c postgres CreateSharedMemoryAndSemaphores + 0x59c
5    0x87b574 postgres PostmasterMain + 0xc64
6    0x780ada postgres main + 0x4da
7    0x31ba21ecdd libc.so.6 __libc_start_main + 0xfd
8    0x47cc19 postgres  + 0x47cc19 


As indicated by the error , the issue is due to improper kernel settings for semaphore and here there are not enough semaphores available at OS level.

Please NOTE: This error does not mean that you have run out of disk space.


  • Please refer Greenplum Database Installation Guide for recommended OS kernel parameters.
  • If the values are default as recommended on the Installation Guide , please verify if the values are set in double quotes, kernel will consider default values when used with quotes.
Current setting:
$ cat /etc/sysctl.conf |grep sem
kernel.sem="250 512000 100 2048”

Suggested setting: without double quotes.

$ cat /etc/sysctl.conf |grep sem 
kernel.sem = 250 512000 100 2048 

Verify with “sysctl -a |grep sem” command to see current setting rather than checking in /etc/sysctl.conf file.

sysctl -a |grep sem
kernel.sem = 250     512000     200     2048 


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