The situation I have a postgresql 9.2 database which is quite heavily updated all the time. The system is hence I/O bound, and I'm currently considering making another upgrade, I just need some directions on where to start improving.
Here is a picture of how the situation looked the past 3 months:
As you can see, update operations accounts for most of the disk utilization. Here is another picture of how the situation looks in a more detailed 3 hour window:
As you can see, the peak write rate is around 20MB/s
Software
The server is running ubuntu 12.04 and postgresql 9.2.
The type of updates are small updated typically on individual rows identified by ID. E.g. UPDATE cars SET price=some_price, updated_at = some_time_stamp WHERE id = some_id.
I have removed and optimized indexes as much as I think is possible, and the servers configuration (both linux kernel and postgres conf) is pretty optimized as well.
Hardware The hardware is a dedicated server with 32GB ECC ram, 4x 600GB 15.000 rpm SAS disks in a RAID 10 array, controlled by an LSI raid controller with BBU and a Intel Xeon E3-1245 Quadcore processor.
Questions
- Is the performance seen by the graphs reasonable for a system of this caliber (read/writes)?
- Should I hence focus on doing a hardware upgrade or investigate deeper into the software (kernel tweaking, confs, queries etc.)?
- If doing a hardware upgrade, is the number of disks key to performance?
------------------------------UPDATE-----------------------------------
I have now upgraded my database server with four intel 520 SSDs instead of the old 15k SAS disks. I'm using the same raid controller. Things has improved quite a lot, as you can see from the following the peak I/O performance has improved around 6-10 times - and that's great!.
However, I was expecting something more like a 20-50 times improvement according to the answers and the I/O capabilities of the new SSDs. So here goes another question.
New question Is there something in my current configuration, that is limiting the I/O performance of my system (where is the bottleneck)?
My configurations:
/etc/postgresql/9.2/main/postgresql.conf
data_directory = '/var/lib/postgresql/9.2/main'
hba_file = '/etc/postgresql/9.2/main/pg_hba.conf'
ident_file = '/etc/postgresql/9.2/main/pg_ident.conf'
external_pid_file = '/var/run/postgresql/9.2-main.pid'
listen_addresses = '192.168.0.4, localhost'
port = 5432
unix_socket_directory = '/var/run/postgresql'
wal_level = hot_standby
synchronous_commit = on
checkpoint_timeout = 10min
archive_mode = on
archive_command = 'rsync -a %p [email protected]:/var/lib/postgresql/9.2/wals/%f </dev/null'
max_wal_senders = 1
wal_keep_segments = 32
hot_standby = on
log_line_prefix = '%t '
datestyle = 'iso, mdy'
lc_messages = 'en_US.UTF-8'
lc_monetary = 'en_US.UTF-8'
lc_numeric = 'en_US.UTF-8'
lc_time = 'en_US.UTF-8'
default_text_search_config = 'pg_catalog.english'
default_statistics_target = 100
maintenance_work_mem = 1920MB
checkpoint_completion_target = 0.7
effective_cache_size = 22GB
work_mem = 160MB
wal_buffers = 16MB
checkpoint_segments = 32
shared_buffers = 7680MB
max_connections = 400
/etc/sysctl.conf
# sysctl config
#net.ipv4.ip_forward=1
net.ipv4.conf.all.rp_filter=1
net.ipv4.icmp_echo_ignore_broadcasts=1
# ipv6 settings (no autoconfiguration)
net.ipv6.conf.default.autoconf=0
net.ipv6.conf.default.accept_dad=0
net.ipv6.conf.default.accept_ra=0
net.ipv6.conf.default.accept_ra_defrtr=0
net.ipv6.conf.default.accept_ra_rtr_pref=0
net.ipv6.conf.default.accept_ra_pinfo=0
net.ipv6.conf.default.accept_source_route=0
net.ipv6.conf.default.accept_redirects=0
net.ipv6.conf.default.forwarding=0
net.ipv6.conf.all.autoconf=0
net.ipv6.conf.all.accept_dad=0
net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.all.accept_ra_defrtr=0
net.ipv6.conf.all.accept_ra_rtr_pref=0
net.ipv6.conf.all.accept_ra_pinfo=0
net.ipv6.conf.all.accept_source_route=0
net.ipv6.conf.all.accept_redirects=0
net.ipv6.conf.all.forwarding=0
# Updated according to postgresql tuning
vm.dirty_ratio = 10
vm.dirty_background_ratio = 1
vm.swappiness = 0
vm.overcommit_memory = 2
kernel.sched_autogroup_enabled = 0
kernel.sched_migration_cost = 50000000
/etc/sysctl.d/30-postgresql-shm.conf
# Shared memory settings for PostgreSQL
# Note that if another program uses shared memory as well, you will have to
# coordinate the size settings between the two.
# Maximum size of shared memory segment in bytes
#kernel.shmmax = 33554432
# Maximum total size of shared memory in pages (normally 4096 bytes)
#kernel.shmall = 2097152
kernel.shmmax = 8589934592
kernel.shmall = 17179869184
# Updated according to postgresql tuning
Output of MegaCli64 -LDInfo -LAll -aAll
Adapter 0 -- Virtual Drive Information:
Virtual Drive: 0 (Target Id: 0)
Name :
RAID Level : Primary-1, Secondary-0, RAID Level Qualifier-0
Size : 446.125 GB
Sector Size : 512
Is VD emulated : No
Mirror Data : 446.125 GB
State : Optimal
Strip Size : 64 KB
Number Of Drives per span:2
Span Depth : 2
Default Cache Policy: WriteBack, ReadAhead, Direct, Write Cache OK if Bad BBU
Current Cache Policy: WriteBack, ReadAhead, Direct, Write Cache OK if Bad BBU
Default Access Policy: Read/Write
Current Access Policy: Read/Write
Disk Cache Policy : Disk's Default
Encryption Type : None
Is VD Cached: No
synchronous_commit = off, after reading the docs at postgresql.org/docs/9.2/static/wal-async-commit.html. (3). What does your configuration look like? Eg. results of this query:SELECT name, current_setting(name), source FROM pg_settings WHERE source NOT IN ('default', 'override');synchronous_commit: 'Asynchronous commit is an option that allows transactions to complete more quickly, at the cost that the most recent transactions may be lost if the database should crash.'