Re: [PERFORM] Stalls on PGSemaphoreLock
Hi all - I am a little delayed in reporting back on this issue, but it was indeed the hugepage defrag setting that was the cause of my issue. One item that we noticed as we were testing this issue that I wanted to report back to the forum is that these settings cat /sys/kernel/mm/transparent_hugepage/defrag always [never] cat /sys/kernel/mm/transparent_hugepage/enabled always [never] Were not sicky on reboot for my version of CentOS, which probably explains why I thought this was disabled already only to have it crop back up. Anyway, I wanted to report back these findings to close the loop on this and to thank the community again for their support. Best, Matt From: Pavy Philippe [philippe.p...@worldline.com] Sent: Tuesday, March 25, 2014 4:10 PM To: Matthew Spilich; pgsql-performance@postgresql.org Subject: RE: [PERFORM] Stalls on PGSemaphoreLock Here, we were the transparent hugepage always actif: cat /sys/kernel/mm/redhat_transparent_hugepage/enabled [always] never We changed to: cat /sys/kernel/mm/redhat_transparent_hugepage/enabled always [never] For the semaphore, our initial configuration was: cat /proc/sys/kernel/sem 250 32000 32 128 And we changed to: cat /proc/sys/kernel/sem 5010641280 5010128 -Message d'origine- De : pgsql-performance-ow...@postgresql.org [mailto:pgsql-performance-ow...@postgresql.org] De la part de Matthew Spilich Envoyé : mardi 25 mars 2014 19:38 À : pgsql-performance@postgresql.org Objet : Re: [PERFORM] Stalls on PGSemaphoreLock Thanks all: Ray: Thanks, we started to look at the hardware/firmware, but didn't get to the the level of detail or running sar. I will probably collect more detail in this area if I continue to see issues. Pavy - I hope that you are right that the hugepage setting is the issue. I was under the impression that I had it disabled already because this has been an known issue for us in the past, but it turns out this was not the case for this server in question. I have disabled it at this time, but it will take a few days of running without issue before I am comfortable declaring that this is the solution. Can you elaborate on the change you mention to upgrade the semaphore configuration? I think this is not something I have looked at before. Ashutosh - Thanks for the reply, I started to do that at first. I turned on log_statement=all for a few hours and I generated a few GB of log file, and I didn't want to leave it running in that state for too long because the issue happens every few days, and not on any regular schedule, so I reverted that after collecting a few GB of detail in the pg log. What I'm doing now to sample every few seconds is I think giving me a decent picture of what is going on with the incident occurs and is a level of data collection that I am more comfortable will not impact operations. I am also logging at the level of 'mod' and all duration 500ms. I don't see that large write operations are a contributing factor leading up to these incidents. I'm hoping that disabling the hugepage setting will be the solution to this. I'll check back in a day or two with feedback. Thanks, Matt From: Pavy Philippe [philippe.p...@worldline.com] Sent: Tuesday, March 25, 2014 1:45 PM To: Ray Stell; Matthew Spilich Cc: pgsql-performance@postgresql.org Subject: RE : [PERFORM] Stalls on PGSemaphoreLock Hello Recently I have a similar problem. The first symptom was a freeze of the connection and 100% of CPU SYS during 2 et 10 minutes, 1 or 2 times per day. Connection impossible, slow query. The strace on one backend show a very long system call on semop(). We have a node with 48 cores dans 128 Go of memory. We have disable the hugepage and upgrade the semaphore configuration, and since that time, we no longer have any problem of freeze on our instance. Can you check the hugepage and semaphore configuration on our node ? I am interested in this case, so do not hesitate to let me make a comeback. Thanks. excuse me for my bad english !!! De : pgsql-performance-ow...@postgresql.org [pgsql-performance-ow...@postgresql.org] de la part de Ray Stell [ste...@vt.edu] Date d'envoi : mardi 25 mars 2014 18:17 À : Matthew Spilich Cc : pgsql-performance@postgresql.org Objet : Re: [PERFORM] Stalls on PGSemaphoreLock On Mar 25, 2014, at 8:46 AM, Matthew Spilich wrote: The symptom: The database machine (running postgres 9.1.9 on CentOS 6.4) is running a low utilization most of the time, but once every day or two, it will appear to slow down to the point where queries back up and clients are unable to connect. Once this event occurs, there are lots of concurrent queries, I see slow queries appear in the logs, but there doesn't appear to be anything abnormal that I have been able
Re: [PERFORM] Stalls on PGSemaphoreLock
On Tue, Apr 22, 2014 at 12:12 PM, Matthew Spilich mspil...@tripadvisor.comwrote: Hi all - I am a little delayed in reporting back on this issue, but it was indeed the hugepage defrag setting that was the cause of my issue. The transparent huge pages features seems so bogus for database workloads, that it is one of the first things I disable on new servers (I have tried to let it enabled sometimes, but every time the system was better with it disabled). One item that we noticed as we were testing this issue that I wanted to report back to the forum is that these settings ... Were not sicky on reboot for my version of CentOS, which probably explains why I thought this was disabled already only to have it crop back up. Anyway, I wanted to report back these findings to close the loop on this and to thank the community again for their support. Just changing files at /sys/ is not permanent, so I recommend adding these commands into your /etc/rc.local file: test -f /sys/kernel/mm/transparent_hugepage/enabled echo never /sys/kernel/mm/transparent_hugepage/enabled test -f /sys/kernel/mm/transparent_hugepage/defrag echo never /sys/kernel/mm/transparent_hugepage/defrag The test's are just to make sure the file does exists, as its location changes depending on the distro you are using and may also change on kernel upgrades. It is also possible to add transparent_hugepage=never on grub.conf file, but I personally dislike this option. Regards, -- Matheus de Oliveira Analista de Banco de Dados Dextra Sistemas - MPS.Br nível F! www.dextra.com.br/postgres
Re: [PERFORM] Stalls on PGSemaphoreLock
Hi Pavy! What kernel version/RHEL release are you running on the servers you are experiencing these issues? I'm interested in knowing since I suspect similar issues on some of our database servers. Best regards, Martin -Original Message- From: pgsql-performance-ow...@postgresql.org [mailto:pgsql-performance- ow...@postgresql.org] On Behalf Of Pavy Philippe Sent: den 25 mars 2014 9:10 To: Matthew Spilich; pgsql-performance@postgresql.org Subject: Re: [PERFORM] Stalls on PGSemaphoreLock Here, we were the transparent hugepage always actif: cat /sys/kernel/mm/redhat_transparent_hugepage/enabled [always] never We changed to: cat /sys/kernel/mm/redhat_transparent_hugepage/enabled always [never] For the semaphore, our initial configuration was: cat /proc/sys/kernel/sem 250 32000 32 128 And we changed to: cat /proc/sys/kernel/sem 5010641280 5010128 -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
Re: [PERFORM] Stalls on PGSemaphoreLock
On Mar 25, 2014, at 8:46 AM, Matthew Spilich wrote: Has any on the forum seen something similar? I think I reported similar phenomenon in my SIGMOD 2013 paper (Latch-free data structures for DBMS: design, implementation, and evaluation, http://dl.acm.org/citation.cfm?id=2463720). - 47245 - 0x0037392eb197 in semop () from /lib64/libc.so.6 #0 0x0037392eb197 in semop () from /lib64/libc.so.6 #1 0x005e0c87 in PGSemaphoreLock () #2 0x0061e3af in LWLockAcquire () #3 0x0060aa0f in ReadBuffer_common () #4 0x0060b2e4 in ReadBufferExtended () ... - 47257 - 0x0037392eb197 in semop () from /lib64/libc.so.6 #0 0x0037392eb197 in semop () from /lib64/libc.so.6 #1 0x005e0c87 in PGSemaphoreLock () #2 0x0061e3af in LWLockAcquire () #3 0x0060aa0f in ReadBuffer_common () #4 0x0060b2e4 in ReadBufferExtended () ... These stack trace results indicate that there was heavy contention of LWLocks for buffers. What I observed is that, in a similar situation, there was also heavy contention on spin locks that ensure mutual exclusion of LWLock status data. Those contentions resulted in a sudden increase in CPU utilization, which is consistent with the following description. At the time of the event, we see a spike in system CPU and load average, but we do not see a corresponding spike in disk reads or writes which would indicate IO load. If the cause of the problem is the same as what I observed, a possible instant countermeasure is increasing the value of 'NUM_BUFFER_PARTITIONS' defined in src/include/storage/lwlock.h from 16 to, for example, 128 or 256, and build the binary. # Using latch-free buffer manager, proposed in my paper, would take long time, since it is not unincorporated in the upstream. -- Takashi Horikawa, Ph.D., Knowledge Discovery Research Laboratories, NEC Corporation. smime.p7s Description: S/MIME cryptographic signature
Re: [PERFORM] Stalls on PGSemaphoreLock
Here, we were the transparent hugepage always actif: cat /sys/kernel/mm/redhat_transparent_hugepage/enabled [always] never We changed to: cat /sys/kernel/mm/redhat_transparent_hugepage/enabled always [never] For the semaphore, our initial configuration was: cat /proc/sys/kernel/sem 250 32000 32 128 And we changed to: cat /proc/sys/kernel/sem 5010641280 5010128 -Message d'origine- De : pgsql-performance-ow...@postgresql.org [mailto:pgsql-performance-ow...@postgresql.org] De la part de Matthew Spilich Envoyé : mardi 25 mars 2014 19:38 À : pgsql-performance@postgresql.org Objet : Re: [PERFORM] Stalls on PGSemaphoreLock Thanks all: Ray: Thanks, we started to look at the hardware/firmware, but didn't get to the the level of detail or running sar. I will probably collect more detail in this area if I continue to see issues. Pavy - I hope that you are right that the hugepage setting is the issue. I was under the impression that I had it disabled already because this has been an known issue for us in the past, but it turns out this was not the case for this server in question. I have disabled it at this time, but it will take a few days of running without issue before I am comfortable declaring that this is the solution. Can you elaborate on the change you mention to upgrade the semaphore configuration? I think this is not something I have looked at before. Ashutosh - Thanks for the reply, I started to do that at first. I turned on log_statement=all for a few hours and I generated a few GB of log file, and I didn't want to leave it running in that state for too long because the issue happens every few days, and not on any regular schedule, so I reverted that after collecting a few GB of detail in the pg log. What I'm doing now to sample every few seconds is I think giving me a decent picture of what is going on with the incident occurs and is a level of data collection that I am more comfortable will not impact operations. I am also logging at the level of 'mod' and all duration 500ms. I don't see that large write operations are a contributing factor leading up to these incidents. I'm hoping that disabling the hugepage setting will be the solution to this. I'll check back in a day or two with feedback. Thanks, Matt From: Pavy Philippe [philippe.p...@worldline.com] Sent: Tuesday, March 25, 2014 1:45 PM To: Ray Stell; Matthew Spilich Cc: pgsql-performance@postgresql.org Subject: RE : [PERFORM] Stalls on PGSemaphoreLock Hello Recently I have a similar problem. The first symptom was a freeze of the connection and 100% of CPU SYS during 2 et 10 minutes, 1 or 2 times per day. Connection impossible, slow query. The strace on one backend show a very long system call on semop(). We have a node with 48 cores dans 128 Go of memory. We have disable the hugepage and upgrade the semaphore configuration, and since that time, we no longer have any problem of freeze on our instance. Can you check the hugepage and semaphore configuration on our node ? I am interested in this case, so do not hesitate to let me make a comeback. Thanks. excuse me for my bad english !!! De : pgsql-performance-ow...@postgresql.org [pgsql-performance-ow...@postgresql.org] de la part de Ray Stell [ste...@vt.edu] Date d'envoi : mardi 25 mars 2014 18:17 À : Matthew Spilich Cc : pgsql-performance@postgresql.org Objet : Re: [PERFORM] Stalls on PGSemaphoreLock On Mar 25, 2014, at 8:46 AM, Matthew Spilich wrote: The symptom: The database machine (running postgres 9.1.9 on CentOS 6.4) is running a low utilization most of the time, but once every day or two, it will appear to slow down to the point where queries back up and clients are unable to connect. Once this event occurs, there are lots of concurrent queries, I see slow queries appear in the logs, but there doesn't appear to be anything abnormal that I have been able to see that causes this behavior. ... Has any on the forum seen something similar? Any suggestions on what to look at next?If it is helpful to describe the server hardware, it's got 2 E5-2670 cpu and 256 GB of ram, and the database is hosted on 1.6TB raid 10 local storage (15K 300 GB drives). I could be way off here, but years ago I experienced something like this (in oracle land) and after some stressful chasing, the marginal failure of the raid controller revealed itself. Same kind of event, steady traffic and then some i/o would not complete and normal ops would stack up. Anyway, what you report reminded me of that event. The E5 is a few years old, I wonder if the raid controller firmware needs a patch? I suppose a marginal power supply might cause a similar hang. Anyway, marginal failures are very painful. Have you checked sar or OS logging at event time? Ce message et les pièces
RE : [PERFORM] Stalls on PGSemaphoreLock
Hello Recently I have a similar problem. The first symptom was a freeze of the connection and 100% of CPU SYS during 2 et 10 minutes, 1 or 2 times per day. Connection impossible, slow query. The strace on one backend show a very long system call on semop(). We have a node with 48 cores dans 128 Go of memory. We have disable the hugepage and upgrade the semaphore configuration, and since that time, we no longer have any problem of freeze on our instance. Can you check the hugepage and semaphore configuration on our node ? I am interested in this case, so do not hesitate to let me make a comeback. Thanks. excuse me for my bad english !!! De : pgsql-performance-ow...@postgresql.org [pgsql-performance-ow...@postgresql.org] de la part de Ray Stell [ste...@vt.edu] Date d'envoi : mardi 25 mars 2014 18:17 À : Matthew Spilich Cc : pgsql-performance@postgresql.org Objet : Re: [PERFORM] Stalls on PGSemaphoreLock On Mar 25, 2014, at 8:46 AM, Matthew Spilich wrote: The symptom: The database machine (running postgres 9.1.9 on CentOS 6.4) is running a low utilization most of the time, but once every day or two, it will appear to slow down to the point where queries back up and clients are unable to connect. Once this event occurs, there are lots of concurrent queries, I see slow queries appear in the logs, but there doesn't appear to be anything abnormal that I have been able to see that causes this behavior. ... Has any on the forum seen something similar? Any suggestions on what to look at next?If it is helpful to describe the server hardware, it's got 2 E5-2670 cpu and 256 GB of ram, and the database is hosted on 1.6TB raid 10 local storage (15K 300 GB drives). I could be way off here, but years ago I experienced something like this (in oracle land) and after some stressful chasing, the marginal failure of the raid controller revealed itself. Same kind of event, steady traffic and then some i/o would not complete and normal ops would stack up. Anyway, what you report reminded me of that event. The E5 is a few years old, I wonder if the raid controller firmware needs a patch? I suppose a marginal power supply might cause a similar hang. Anyway, marginal failures are very painful. Have you checked sar or OS logging at event time? Ce message et les pièces jointes sont confidentiels et réservés à l'usage exclusif de ses destinataires. Il peut également être protégé par le secret professionnel. Si vous recevez ce message par erreur, merci d'en avertir immédiatement l'expéditeur et de le détruire. L'intégrité du message ne pouvant être assurée sur Internet, la responsabilité de Worldline ne pourra être recherchée quant au contenu de ce message. Bien que les meilleurs efforts soient faits pour maintenir cette transmission exempte de tout virus, l'expéditeur ne donne aucune garantie à cet égard et sa responsabilité ne saurait être recherchée pour tout dommage résultant d'un virus transmis. This e-mail and the documents attached are confidential and intended solely for the addressee; it may also be privileged. If you receive this e-mail in error, please notify the sender immediately and destroy it. As its integrity cannot be secured on the Internet, the Worldline liability cannot be triggered for the message content. Although the sender endeavours to maintain a computer virus-free network, the sender does not warrant that this transmission is virus-free and will not be liable for any damages resulting from any virus transmitted. -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
[PERFORM] Stalls on PGSemaphoreLock
Hi everyone! I've been working on a puzzling issue for a few days am am hoping that someone has seen something similar or can help. There have been some odd behaviors on one of my production facing postgres servers. version info from postgres: PostgreSQL 9.1.9 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4), 64-bit The symptom: The database machine (running postgres 9.1.9 on CentOS 6.4) is running a low utilization most of the time, but once every day or two, it will appear to slow down to the point where queries back up and clients are unable to connect. Once this event occurs, there are lots of concurrent queries, I see slow queries appear in the logs, but there doesn't appear to be anything abnormal that I have been able to see that causes this behavior. The event will occur just long enough for monitoring to alarm. We will respond to alerts to take a look, but within a minute or three at most, load returns back to normal levels and all running queries complete in expected times. At the time of the event, we see a spike in system CPU and load average, but we do not see a corresponding spike in disk reads or writes which would indicate IO load. Initial troubleshooting to monitor active processes led us to see a flurry of activity in ps waiting on semtimedop. Our efforts internally to diagnose this problem are to sample pg_locks and pg_stat_activity every 5s plus running a script to look for at least one postgres process waiting on a semaphore, and if it finds one, it gets a stack trace of every running postgres processes with GDB. It also uses strace on 5 processes to find out which semaphore they're waiting on. What we were catching in the following stack trace seems to be representative of where things are waiting when we see an event - here are two examples that are representative - lots of threads will appear to be in this state: - 47245 - 0x0037392eb197 in semop () from /lib64/libc.so.6 #0 0x0037392eb197 in semop () from /lib64/libc.so.6 #1 0x005e0c87 in PGSemaphoreLock () #2 0x0061e3af in LWLockAcquire () #3 0x0060aa0f in ReadBuffer_common () #4 0x0060b2e4 in ReadBufferExtended () #5 0x0047708d in _bt_relandgetbuf () #6 0x0047aac4 in _bt_search () #7 0x0047af8d in _bt_first () #8 0x00479704 in btgetbitmap () #9 0x006e7e00 in FunctionCall2Coll () #10 0x00473120 in index_getbitmap () #11 0x005726b8 in MultiExecBitmapIndexScan () #12 0x0057214d in BitmapHeapNext () #13 0x0056b18e in ExecScan () #14 0x00563ed8 in ExecProcNode () #15 0x00562d72 in standard_ExecutorRun () #16 0x0062ce67 in PortalRunSelect () #17 0x0062e128 in PortalRun () #18 0x0062bb66 in PostgresMain () #19 0x005ecd01 in ServerLoop () #20 0x005ef401 in PostmasterMain () #21 0x00590ff8 in main () - 47257 - 0x0037392eb197 in semop () from /lib64/libc.so.6 #0 0x0037392eb197 in semop () from /lib64/libc.so.6 #1 0x005e0c87 in PGSemaphoreLock () #2 0x0061e3af in LWLockAcquire () #3 0x0060aa0f in ReadBuffer_common () #4 0x0060b2e4 in ReadBufferExtended () #5 0x0047708d in _bt_relandgetbuf () #6 0x0047aac4 in _bt_search () #7 0x0047af8d in _bt_first () #8 0x004797d1 in btgettuple () #9 0x006e7e00 in FunctionCall2Coll () #10 0x0047339d in index_getnext () #11 0x00575ed6 in IndexNext () #12 0x0056b18e in ExecScan () #13 0x00563ee8 in ExecProcNode () #14 0x00562d72 in standard_ExecutorRun () #15 0x0062ce67 in PortalRunSelect () #16 0x0062e128 in PortalRun () #17 0x0062bb66 in PostgresMain () #18 0x005ecd01 in ServerLoop () #19 0x005ef401 in PostmasterMain () #20 0x00590ff8 in main () Has any on the forum seen something similar? Any suggestions on what to look at next?If it is helpful to describe the server hardware, it's got 2 E5-2670 cpu and 256 GB of ram, and the database is hosted on 1.6TB raid 10 local storage (15K 300 GB drives). The workload is predominantly read and the queries are mostly fairly simple selects from a single large table generally specifying the primary key as part of the where clause along with a few other filters. Thanks, Matt
Re: [PERFORM] Stalls on PGSemaphoreLock
On Mar 25, 2014, at 8:46 AM, Matthew Spilich wrote: The symptom: The database machine (running postgres 9.1.9 on CentOS 6.4) is running a low utilization most of the time, but once every day or two, it will appear to slow down to the point where queries back up and clients are unable to connect. Once this event occurs, there are lots of concurrent queries, I see slow queries appear in the logs, but there doesn't appear to be anything abnormal that I have been able to see that causes this behavior. ... Has any on the forum seen something similar? Any suggestions on what to look at next?If it is helpful to describe the server hardware, it's got 2 E5-2670 cpu and 256 GB of ram, and the database is hosted on 1.6TB raid 10 local storage (15K 300 GB drives). I could be way off here, but years ago I experienced something like this (in oracle land) and after some stressful chasing, the marginal failure of the raid controller revealed itself. Same kind of event, steady traffic and then some i/o would not complete and normal ops would stack up. Anyway, what you report reminded me of that event. The E5 is a few years old, I wonder if the raid controller firmware needs a patch? I suppose a marginal power supply might cause a similar hang. Anyway, marginal failures are very painful. Have you checked sar or OS logging at event time?
Re: [PERFORM] Stalls on PGSemaphoreLock
Thanks all: Ray: Thanks, we started to look at the hardware/firmware, but didn't get to the the level of detail or running sar. I will probably collect more detail in this area if I continue to see issues. Pavy - I hope that you are right that the hugepage setting is the issue. I was under the impression that I had it disabled already because this has been an known issue for us in the past, but it turns out this was not the case for this server in question. I have disabled it at this time, but it will take a few days of running without issue before I am comfortable declaring that this is the solution. Can you elaborate on the change you mention to upgrade the semaphore configuration? I think this is not something I have looked at before. Ashutosh - Thanks for the reply, I started to do that at first. I turned on log_statement=all for a few hours and I generated a few GB of log file, and I didn't want to leave it running in that state for too long because the issue happens every few days, and not on any regular schedule, so I reverted that after collecting a few GB of detail in the pg log. What I'm doing now to sample every few seconds is I think giving me a decent picture of what is going on with the incident occurs and is a level of data collection that I am more comfortable will not impact operations. I am also logging at the level of 'mod' and all duration 500ms. I don't see that large write operations are a contributing factor leading up to these incidents. I'm hoping that disabling the hugepage setting will be the solution to this. I'll check back in a day or two with feedback. Thanks, Matt From: Pavy Philippe [philippe.p...@worldline.com] Sent: Tuesday, March 25, 2014 1:45 PM To: Ray Stell; Matthew Spilich Cc: pgsql-performance@postgresql.org Subject: RE : [PERFORM] Stalls on PGSemaphoreLock Hello Recently I have a similar problem. The first symptom was a freeze of the connection and 100% of CPU SYS during 2 et 10 minutes, 1 or 2 times per day. Connection impossible, slow query. The strace on one backend show a very long system call on semop(). We have a node with 48 cores dans 128 Go of memory. We have disable the hugepage and upgrade the semaphore configuration, and since that time, we no longer have any problem of freeze on our instance. Can you check the hugepage and semaphore configuration on our node ? I am interested in this case, so do not hesitate to let me make a comeback. Thanks. excuse me for my bad english !!! De : pgsql-performance-ow...@postgresql.org [pgsql-performance-ow...@postgresql.org] de la part de Ray Stell [ste...@vt.edu] Date d'envoi : mardi 25 mars 2014 18:17 À : Matthew Spilich Cc : pgsql-performance@postgresql.org Objet : Re: [PERFORM] Stalls on PGSemaphoreLock On Mar 25, 2014, at 8:46 AM, Matthew Spilich wrote: The symptom: The database machine (running postgres 9.1.9 on CentOS 6.4) is running a low utilization most of the time, but once every day or two, it will appear to slow down to the point where queries back up and clients are unable to connect. Once this event occurs, there are lots of concurrent queries, I see slow queries appear in the logs, but there doesn't appear to be anything abnormal that I have been able to see that causes this behavior. ... Has any on the forum seen something similar? Any suggestions on what to look at next?If it is helpful to describe the server hardware, it's got 2 E5-2670 cpu and 256 GB of ram, and the database is hosted on 1.6TB raid 10 local storage (15K 300 GB drives). I could be way off here, but years ago I experienced something like this (in oracle land) and after some stressful chasing, the marginal failure of the raid controller revealed itself. Same kind of event, steady traffic and then some i/o would not complete and normal ops would stack up. Anyway, what you report reminded me of that event. The E5 is a few years old, I wonder if the raid controller firmware needs a patch? I suppose a marginal power supply might cause a similar hang. Anyway, marginal failures are very painful. Have you checked sar or OS logging at event time? Ce message et les pièces jointes sont confidentiels et réservés à l'usage exclusif de ses destinataires. Il peut également être protégé par le secret professionnel. Si vous recevez ce message par erreur, merci d'en avertir immédiatement l'expéditeur et de le détruire. L'intégrité du message ne pouvant être assurée sur Internet, la responsabilité de Worldline ne pourra être recherchée quant au contenu de ce message. Bien que les meilleurs efforts soient faits pour maintenir cette transmission exempte de tout virus, l'expéditeur ne donne aucune garantie à cet égard et sa responsabilité ne saurait être recherchée pour tout dommage résultant d'un virus transmis. This e-mail and the documents attached are confidential
Re: [PERFORM] Stalls on PGSemaphoreLock
2014-03-25, Matthew Spilich mspil...@tripadvisor.com: Has any on the forum seen something similar? Any suggestions on what to look at next?If it is helpful to describe the server hardware, it's got 2 E5-2670 cpu and 256 GB of ram, and the database is hosted on 1.6TB raid 10 local storage (15K 300 GB drives). The workload is predominantly read and the queries are mostly fairly simple selects from a single large table generally specifying the primary key as part of the where clause along with a few other filters. I have seen something similar. It was because of large shared_buffers.
