Hi,
Well, unfortunately I still need community help.
-- Environment
OS: Centos CentOS Linux release 7.2.1511
Kernel: 3.10.0-327.36.3.el7.x86_64
PostgreSQL: 9.6.3
-- Hardware
Server: Dell PowerEdge R430
CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
Raid controller: PERC H730 Mini (1GB cache)
Disks: 8 x 10K RPM SAS 12GB/s 2.5 (ST1200MM0088) in RAID 6
RAM: 192GB (M393A2G40DB0-CPB x 16)
For more detailed hardware info please see attached configuration.txt
-- postgresql.conf
max_connections = 2048
shared_buffers = 48GB
temp_buffers = 128MB
work_mem = 256MB
maintenance_work_mem = 512MB
dynamic_shared_memory_type = posix
wal_level = hot_standby
min_wal_size = 4GB
max_wal_size = 32GB
huge_pages = on
+
numactl interleave=all
-- sysctl.conf
kernel.shmmax=64424509440
kernel.shmall=4294967296
kernel.sem = 1024 32767 128 16384
fs.aio-max-nr=3145728
fs.file-max = 6815744
net.core.rmem_default=262144
net.core.rmem_max=4194304
net.core.wmem_default=262144
net.core.wmem_max=1048586
vm.nr_hugepages=33000
vm.dirty_background_bytes=67108864
vm.dirty_bytes=536870912
vm.min_free_kbytes=1048576
zone_reclaim_mode=0
Again: problem is the occasional long inserts that can happen 1-5 times per day
on OLTP system.
No autovacuum performed during long inserts. WAL rate is 1-2Gb per hour, no
correlation spotted with this issue.
Wait event "buffer_mapping" happen for appropriate transactions but not every
time (maybe just not every time catched).
I have two suspects for such behaviour: I/O system and high concurrency.
There is a problem with one application that frequently recreates up to 90
sessions but investigation shows that there is no direct correlation between
such sessions and long transactions, at least it is not the root cause of the
issue (of course such app behaviour will be fixed).
The investigation and tracing with strace in particular showed that:
1. The only long event straced from postgres backends was <... semop resumed>.
2. Seems the whole host gets hung during such events.
Example:
Java application located on separate host reports several long transactions:
123336.943 - [1239588mks]: event.insert-table
123336.943 - [1240827mks]: event.insert-table
123337.019 - [1292534mks]: event.insert-table
143353.542 - [5467657mks]: event.insert-table
143353.543 - [5468884mks]: event.insert-table
152338.763 - [1264588mks]: event.insert-table
152338.765 - [2054887mks]: event.insert-table
Strace output for event happened at 14:33 with particular known pid:
119971 14:33:48.075375 epoll_wait(3, <unfinished ...>
119971 14:33:48.075696 <... epoll_wait resumed> {{EPOLLIN, {u32=27532016,
u64=27532016}}}, 1, -1) = 1 <0.000313>
119971 14:33:48.075792 recvfrom(9, <unfinished ...>
119971 14:33:48.075866 <... recvfrom resumed>
"B\0\0\3\27\0S_21\0\0*\0\1\0\1\0\1\0\0\0\0\0\1\0\1\0\0\0\0\0"..., 8192, 0,
NULL, NULL) = 807 <0.000066>
119971 14:33:48.076243 semop(26706044, {{8, -1, 0}}, 1 <unfinished ...>
120019 14:33:48.119971 recvfrom(9, <unfinished ...>
119971 14:33:53.491029 <... semop resumed> ) = 0 <5.414772>
119971 14:33:53.500356 lseek(18, 0, SEEK_END <unfinished ...>
119971 14:33:53.500436 <... lseek resumed> ) = 107790336 <0.000072>
119971 14:33:53.500514 lseek(20, 0, SEEK_END <unfinished ...>
Checking strace long semop calls for whole day:
root@host [20180314 17:47:36]:/home/user$ egrep " <[1-9]." /tmp/strace | grep
semop
119991 12:33:36 <... semop resumed> ) = 0 <1.419394>
119942 12:33:36 <... semop resumed> ) = 0 <1.422554>
119930 12:33:36 <... semop resumed> ) = 0 <1.414916>
119988 12:33:36 <... semop resumed> ) = 0 <1.213309>
119966 12:33:36 <... semop resumed> ) = 0 <1.237492>
119958 14:33:53.489398 <... semop resumed> ) = 0 <5.455830>
120019 14:33:53.490613 <... semop resumed> ) = 0 <5.284505>
119997 14:33:53.490638 <... semop resumed> ) = 0 <5.111661>
120000 14:33:53.490649 <... semop resumed> ) = 0 <3.521992>
119991 14:33:53.490660 <... semop resumed> ) = 0 <2.522460>
119988 14:33:53.490670 <... semop resumed> ) = 0 <5.252485>
120044 14:33:53.490834 <... semop resumed> ) = 0 <1.718129>
119976 14:33:53.490852 <... semop resumed> ) = 0 <2.489563>
119974 14:33:53.490862 <... semop resumed> ) = 0 <1.520801>
119984 14:33:53.491011 <... semop resumed> ) = 0 <1.213411>
119971 14:33:53.491029 <... semop resumed> ) = 0 <5.414772>
119969 14:33:53.491039 <... semop resumed> ) = 0 <2.275608>
119966 14:33:53.491048 <... semop resumed> ) = 0 <2.526024>
119942 14:33:53.491058 <... semop resumed> ) = 0 <5.448506>
119964 15:23:38.746394 <... semop resumed> ) = 0 <2.034851>
119960 15:23:38.746426 <... semop resumed> ) = 0 <2.038321>
119966 15:23:38.752646 <... semop resumed> ) = 0 <1.252342>
Also it was spotted that WALWriter Postgres backend also spend time in <semop
resumed> during hangs.
Also I have application on db host that performs pg_stat_activity shapshots
every 500m and for example I can see that there were no snapshot between
14:33:47 and 14:33:53.
Separate simple script on db host every ~100ms checks ps output for this
application and writes it into the txt file. And we can see that while it
usually performs about 7-8 times per second, between 14:33:47 and 14:33:53 it
couldn't even perform enough ps calls. Strace for this backend showed that this
process was hung in semop call. So it tells me that whole system gets hung.
14:33:40 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:41 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:42 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:43 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:44 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:45 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:46 TOTAL=6 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:47 TOTAL=2 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:48 TOTAL=3 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:49 TOTAL=2 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:50 TOTAL=2 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:51 TOTAL=2 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:52 TOTAL=4 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:53 TOTAL=6 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:54 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
14:33:55 TOTAL=7 wait_transaction_locked=0 sleep_on_page=0 get_request=0
sleep_on_buffer=0
I understand that RAID-6 is not the best option, but I can't catch any evidence
telling that system run out of 1GB RAID controller cache on writes.
Please assist in understanding meaning and nature of long semop calls
appearances.
--
Regards,
Pavel Suderevsky
From: Pavel Suderevsky
Sent: Monday, January 22, 2018 21:43
To: [email protected]
Subject: PG 9.6 Slow inserts with long-lasting LWLocks
Hi,
I have an issue with sporadic slow insert operations with query duration more
than 1 sec while it takes about 50ms in average.
Configuration:
OS: Centos 7.2.151
PostgreSQL: 9.6.3
CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
Memory: total used free shared buff/cache
available
Mem: 193166 10324 1856 44522 180985
137444
Swap: 0 0 0
Storage: Well, about 4gb of BBU write cache.
shared_buffers = 32gb
work_mem = 128mb
max_pred_locks_per_transaction = 8192
This can occur once a day or not happen for few days while system load is the
same. "Inserts" are the prepared statement batches with 4-5 inserts.
Neither excessive memory usage nor disk or cpu utilizations have been catched.
Wal writing rates, checkpoints, anything else from pg_stat_* tables were
checked and nothing embarrassing was found.
There are several scenarious of such long inserts were spotted:
1. No any locks catched (500ms check intervals)
2. Wait event is "buffer_mapping" - looks like the most common case
snaphot time | state | trx duration | query
duration | wait_event_type | wait_event | query
2017-12-22 03:16:01.181014 | active | 00:00:00.535309 | 00:00:00.524729 |
LWLockTranche | buffer_mapping | INSERT INTO table..
2017-12-22 03:16:00.65814 | active | 00:00:00.012435 | 00:00:00.001855 |
LWLockTranche | buffer_mapping | INSERT INTO table..
3. Wait event is "SerializablePredicateLockListLock" (I believe the same root
cause as previous case)
4. No any locks catched, but ~39 other backends in parallel are active
I assumed that it can be somehow related to enabled NUMA, but it looks like
memory is allocated evenly, zone_reclaim_mode is 0.
numactl --hardware
available: 2 nodes (0-1)
node 0 cpus: 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46
node 0 size: 130978 MB
node 0 free: 1251 MB
node 1 cpus: 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47
node 1 size: 65536 MB
node 1 free: 42 MB
node distances:
node 0 1
0: 10 21
1: 21 10
numastat -m
Per-node system memory usage (in MBs):
Node 0 Node 1 Total
--------------- --------------- ---------------
MemTotal 130978.34 65536.00 196514.34
MemFree 1479.07 212.12 1691.20
MemUsed 129499.27 65323.88 194823.14
Active 72241.16 37254.56 109495.73
Inactive 47936.24 24205.40 72141.64
Active(anon) 21162.41 18978.96 40141.37
Inactive(anon) 1061.94 7522.34 8584.27
Active(file) 51078.76 18275.60 69354.36
Inactive(file) 46874.30 16683.06 63557.36
Unevictable 0.00 0.00 0.00
Mlocked 0.00 0.00 0.00
Dirty 0.04 0.02 0.05
Writeback 0.00 0.00 0.00
FilePages 116511.36 60923.16 177434.52
Mapped 16507.29 23912.82 40420.11
AnonPages 3661.55 530.26 4191.81
Shmem 18558.28 25964.74 44523.02
KernelStack 16.98 5.77 22.75
PageTables 3943.56 1022.25 4965.81
NFS_Unstable 0.00 0.00 0.00
Bounce 0.00 0.00 0.00
WritebackTmp 0.00 0.00 0.00
Slab 2256.09 1291.53 3547.61
SReclaimable 2108.29 889.85 2998.14
SUnreclaim 147.80 401.68 549.47
AnonHugePages 1824.00 284.00 2108.00
HugePages_Total 0.00 0.00 0.00
HugePages_Free 0.00 0.00 0.00
HugePages_Surp 0.00 0.00 0.00
$ cat /proc/62679/numa_maps | grep N0 | grep zero
7f92509d3000 prefer:0 file=/dev/zero\040(deleted) dirty=8419116 mapmax=154
active=8193350 N0=3890534 N1=4528582 kernelpagesize_kB=4
Could you advise what can cause such occasional long inserts with long-lasting
LWlocks?
root@dbhost [20180314 16:23:44]:/home/user$ lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 48
On-line CPU(s) list: 0-47
Thread(s) per core: 2
Core(s) per socket: 12
Socket(s): 2
NUMA node(s): 2
Vendor ID: GenuineIntel
CPU family: 6
Model: 63
Model name: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
Stepping: 2
CPU MHz: 2900.000
BogoMIPS: 4998.18
Virtualization: VT-x
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 30720K
NUMA node0 CPU(s):
0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46
NUMA node1 CPU(s):
1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47
root@dbhost [20180314 17:06:47]:/home/user$ numactl --hardware
available: 2 nodes (0-1)
node 0 cpus: 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46
node 0 size: 130978 MB
node 0 free: 7194 MB
node 1 cpus: 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47
node 1 size: 65536 MB
node 1 free: 642 MB
node distances:
node 0 1
0: 10 21
1: 21 10
root@dbhost [20180314 16:23:46]:/home/user$ numastat -m
Per-node system memory usage (in MBs):
Node 0 Node 1 Total
--------------- --------------- ---------------
MemTotal 130978.34 65536.00 196514.34
MemFree 5897.14 426.93 6324.06
MemUsed 125081.20 65109.07 190190.28
Active 44828.92 16888.00 61716.92
Inactive 42311.52 12586.01 54897.53
Active(anon) 6113.09 4818.25 10931.33
Inactive(anon) 154.44 281.88 436.32
Active(file) 38715.84 12069.75 50785.59
Inactive(file) 42157.08 12304.12 54461.21
Unevictable 0.00 0.00 0.00
Mlocked 0.00 0.00 0.00
Dirty 6.55 0.30 6.85
Writeback 0.00 0.00 0.00
FilePages 81428.38 25263.89 106692.27
Mapped 58.56 26.13 84.69
AnonPages 5767.31 4265.87 10033.18
Shmem 499.60 834.26 1333.86
KernelStack 17.30 5.94 23.23
PageTables 40.75 36.96 77.71
NFS_Unstable 0.00 0.00 0.00
Bounce 0.00 0.00 0.00
WritebackTmp 0.00 0.00 0.00
Slab 1721.68 1056.38 2778.06
SReclaimable 1542.00 864.26 2406.26
SUnreclaim 179.68 192.12 371.80
AnonHugePages 62.00 28.00 90.00
HugePages_Total 33000.00 33000.00 66000.00
HugePages_Free 4450.00 4454.00 8904.00
HugePages_Surp 0.00 0.00 0.00
root@dbhost [20180314 16:25:36]:/home/user$ cat /etc/sysctl.conf
kernel.shmmax=64424509440
kernel.shmall=4294967296
# kernel.sem=<SEMMSL> <SEMMNS> <SEMOPM> <SEMMNI>
kernel.sem = 1024 32767 128 16384
fs.aio-max-nr=3145728
fs.file-max = 6815744
net.core.rmem_default=262144
net.core.rmem_max=4194304
net.core.wmem_default=262144
net.core.wmem_max=1048586
vm.nr_hugepages=33000
vm.dirty_background_bytes=67108864
vm.dirty_bytes=536870912
vm.min_free_kbytes=1048576
root@dbhost [20180314 16:25:49]:/home/user$ free -m
total used free shared buff/cache available
Mem: 193166 77128 6139 1333 109899 110458
Swap: 0 0 0
root@dbhost [20180314 16:28:07]:/home/user$ omreport storage controller
Controller PERC H730 Mini(Embedded)
Controller
ID : 0
Status : Ok
Name : PERC H730 Mini
Slot ID : Embedded
State : Ready
Firmware Version : 25.5.0.0018
Minimum Required Firmware Version : Not Applicable
Driver Version : 06.807.10.00-rh1
Minimum Required Driver Version : Not Applicable
Storport Driver Version : Not Applicable
Minimum Required Storport Driver Version : Not Applicable
Number of Connectors : 2
Rebuild Rate : 30%
BGI Rate : 30%
Check Consistency Rate : 30%
Reconstruct Rate : 30%
Alarm State : Not Applicable
Cluster Mode : Not Applicable
SCSI Initiator ID : Not Applicable
Cache Memory Size : 1024 MB
Patrol Read Mode : Auto
Patrol Read State : Active
Patrol Read Rate : 30%
Patrol Read Iterations : 117
Abort Check Consistency on Error : Disabled
Allow Revertible Hot Spare and Replace Member : Enabled
Load Balance : Not Applicable
Auto Replace Member on Predictive Failure : Disabled
Redundant Path view : Not Applicable
CacheCade Capable : Not Applicable
Persistent Hot Spare : Disabled
Encryption Capable : Yes
Encryption Key Present : No
Encryption Mode : None
Preserved Cache : Not Applicable
Spin Down Unconfigured Drives : Disabled
Spin Down Hot Spares : Disabled
Spin Down Configured Drives : Disabled
Automatic Disk Power Saving (Idle C) : Disabled
Start Time (HH:MM) : Not Applicable
Time Interval for Spin Up (in Hours) : Not Applicable
T10 Protection Information Capable : No
Non-RAID HDD Disk Cache Policy : Unchanged
Current Controller Mode : RAID
root@dbhost [20180314 16:39:01]:/home/user$ omreport storage vdisk controller=0
Virtual Disk 0 on Controller PERC H730 Mini (Embedded)
Controller PERC H730 Mini (Embedded)
ID : 0
Status : Ok
Name : GenericR6_0
State : Ready
Hot Spare Policy violated : Not Assigned
Encrypted : No
Layout : RAID-6
Size : 6,703.50 GB (7197828317184 bytes)
T10 Protection Information Status : No
Associated Fluid Cache State : Not Applicable
Device Name : /dev/sda
Bus Protocol : SAS
Media : HDD
Read Policy : No Read Ahead
Write Policy : Write Back
Cache Policy : Not Applicable
Stripe Element Size : 64 KB
Disk Cache Policy : Unchanged
root@dbhost [20180314 16:31:29]:/home/user$ grep ^Huge /proc/meminfo
HugePages_Total: 33000
HugePages_Free: 4452
HugePages_Rsvd: 2066
HugePages_Surp: 0
Hugepagesize: 2048 kB
=====================
postgresql.conf
max_connections = 2048
shared_buffers = 48GB
temp_buffers = 128MB
work_mem = 256MB
maintenance_work_mem = 512MB
dynamic_shared_memory_type = posix
wal_level = hot_standby
max_wal_senders = 5
wal_keep_segments = 2000
max_replication_slots = 5
min_wal_size = 4GB
max_wal_size = 32GB
archive_mode = on
autovacuum_vacuum_threshold = 100
autovacuum_analyze_threshold = 100
autovacuum_vacuum_scale_factor = 0.02
autovacuum_analyze_scale_factor = 0.01
autovacuum_vacuum_cost_delay = 14
autovacuum_vacuum_cost_limit = 5000
autovacuum_max_workers = 4
