Re: Very poor read performance, query independent

Rick,

Should the number of page should always be correlated to the VmPeak of the
postmaster or could it be set to reflect shared_buffer or another setting?
Thanks!

Charles

On Mon, Jul 10, 2017 at 5:25 PM, Rick Otten <rottenwindfish(at)gmail(dot)com>
wrote:

> Although probably not the root cause, at the least I would set up
> hugepages ( https://www.postgresql.org/docs/9.6/static/kernel-
> resources.html#LINUX-HUGE-PAGES ), and bump effective_io_concurrency up
> quite a bit as well (256 ?).
>
>
> On Mon, Jul 10, 2017 at 10:03 AM, Charles Nadeau <charles(dot)nadeau(at)gmail(dot)com
> > wrote:
>
>> I’m running PostgreSQL 9.6.3 on Ubuntu 16.10 (kernel 4.4.0-85-generic).
>> Hardware is:
>>
>> *2x Intel Xeon E5550
>>
>> *72GB RAM
>>
>> *Hardware RAID10 (4 x 146GB SAS 10k) P410i controller with 1GB FBWC (80%
>> read/20% write) for Postgresql data only:
>>
>> Logical Drive: 3
>>
>> Size: 273.4 GB
>>
>> Fault Tolerance: 1+0
>>
>> Heads: 255
>>
>> Sectors Per Track: 32
>>
>> Cylinders: 65535
>>
>> Strip Size: 128 KB
>>
>> Full Stripe Size: 256 KB
>>
>> Status: OK
>>
>> Caching: Enabled
>>
>> Unique Identifier: 600508B1001037383941424344450A00
>>
>> Disk Name: /dev/sdc
>>
>> Mount Points: /mnt/data 273.4 GB
>>
>> OS Status: LOCKED
>>
>> Logical Drive Label: A00A194750123456789ABCDE516F
>>
>> Mirror Group 0:
>>
>> physicaldrive 2I:1:5 (port 2I:box 1:bay 5, SAS, 146 GB, OK)
>>
>> physicaldrive 2I:1:6 (port 2I:box 1:bay 6, SAS, 146 GB, OK)
>>
>> Mirror Group 1:
>>
>> physicaldrive 2I:1:7 (port 2I:box 1:bay 7, SAS, 146 GB, OK)
>>
>> physicaldrive 2I:1:8 (port 2I:box 1:bay 8, SAS, 146 GB, OK)
>>
>> Drive Type: Data
>>
>> Formatted with ext4 with: sudo mkfs.ext4 -E stride=32,stripe_width=64 -v
>> /dev/sdc1.
>>
>> Mounted in /etc/fstab with this line: "UUID=99fef4ae-51dc-4365-9210-0b153b1cbbd0
>> /mnt/data ext4 rw,nodiratime,user_xattr,noatime,nobarrier,errors=remount-ro
>> 0 1"
>>
>> Postgresql is the only application running on this server.
>>
>>
>> Postgresql is used as a mini data warehouse to generate reports and do
>> statistical analysis. It is used by at most 2 users and fresh data is added
>> every 10 days. The database has 16 tables: one is 224GB big and the rest
>> are between 16kB and 470MB big.
>>
>>
>> My configuration is:
>>
>>
>> name | current_setting | source
>>
>> ---------------------------------+--------------------------
>> ----------------------+----------------------
>>
>> application_name | psql | client
>>
>> autovacuum_vacuum_scale_factor | 0 | configuration file
>>
>> autovacuum_vacuum_threshold | 2000 | configuration file
>>
>> checkpoint_completion_target | 0.9 | configuration file
>>
>> checkpoint_timeout | 30min | configuration file
>>
>> client_encoding | UTF8 | client
>>
>> client_min_messages | log | configuration file
>>
>> cluster_name | 9.6/main | configuration file
>>
>> cpu_index_tuple_cost | 0.001 | configuration file
>>
>> cpu_operator_cost | 0.0005 | configuration file
>>
>> cpu_tuple_cost | 0.003 | configuration file
>>
>> DateStyle | ISO, YMD | configuration file
>>
>> default_statistics_target | 100 | configuration file
>>
>> default_text_search_config | pg_catalog.english | configuration file
>>
>> dynamic_shared_memory_type | posix | configuration file
>>
>> effective_cache_size | 22GB | configuration file
>>
>> effective_io_concurrency | 4 | configuration file
>>
>> external_pid_file | /var/run/postgresql/9.6-main.pid | configuration file
>>
>> lc_messages | C | configuration file
>>
>> lc_monetary | en_CA.UTF-8 | configuration file
>>
>> lc_numeric | en_CA.UTF-8 | configuration file
>>
>> lc_time | en_CA.UTF-8 | configuration file
>>
>> listen_addresses | * | configuration file
>>
>> lock_timeout | 100s | configuration file
>>
>> log_autovacuum_min_duration | 0 | configuration file
>>
>> log_checkpoints | on | configuration file
>>
>> log_connections | on | configuration file
>>
>> log_destination | csvlog | configuration file
>>
>> log_directory | /mnt/bigzilla/data/toburn/hp/postgresql/pg_log |
>> configuration file
>>
>> log_disconnections | on | configuration file
>>
>> log_error_verbosity | default | configuration file
>>
>> log_file_mode | 0600 | configuration file
>>
>> log_filename | postgresql-%Y-%m-%d_%H%M%S.log | configuration file
>>
>> log_line_prefix | user=%u,db=%d,app=%aclient=%h | configuration file
>>
>> log_lock_waits | on | configuration file
>>
>> log_min_duration_statement | 0 | configuration file
>>
>> log_min_error_statement | debug1 | configuration file
>>
>> log_min_messages | debug1 | configuration file
>>
>> log_rotation_size | 1GB | configuration file
>>
>> log_temp_files | 0 | configuration file
>>
>> log_timezone | localtime | configuration file
>>
>> logging_collector | on | configuration file
>>
>> maintenance_work_mem | 3GB | configuration file
>>
>> max_connections | 10 | configuration file
>>
>> max_locks_per_transaction | 256 | configuration file
>>
>> max_parallel_workers_per_gather | 14 | configuration file
>>
>> max_stack_depth | 2MB | environment variable
>>
>> max_wal_size | 4GB | configuration file
>>
>> max_worker_processes | 14 | configuration file
>>
>> min_wal_size | 2GB | configuration file
>>
>> parallel_setup_cost | 1000 | configuration file
>>
>> parallel_tuple_cost | 0.012 | configuration file
>>
>> port | 5432 | configuration file
>>
>> random_page_cost | 22 | configuration file
>>
>> seq_page_cost | 1 | configuration file
>>
>> shared_buffers | 34GB | configuration file
>>
>> shared_preload_libraries | pg_stat_statements | configuration file
>>
>> ssl | on | configuration file
>>
>> ssl_cert_file | /etc/ssl/certs/ssl-cert-snakeoil.pem | configuration file
>>
>> ssl_key_file | /etc/ssl/private/ssl-cert-snakeoil.key | configuration
>> file
>>
>> statement_timeout | 1000000s | configuration file
>>
>> stats_temp_directory | /var/run/postgresql/9.6-main.pg_stat_tmp |
>> configuration file
>>
>> superuser_reserved_connections | 1 | configuration file
>>
>> syslog_facility | local1 | configuration file
>>
>> syslog_ident | postgres | configuration file
>>
>> syslog_sequence_numbers | on | configuration file
>>
>> temp_file_limit | 80GB | configuration file
>>
>> TimeZone | localtime | configuration file
>>
>> track_activities | on | configuration file
>>
>> track_counts | on | configuration file
>>
>> track_functions | all | configuration file
>>
>> unix_socket_directories | /var/run/postgresql | configuration file
>>
>> vacuum_cost_delay | 1ms | configuration file
>>
>> vacuum_cost_limit | 5000 | configuration file
>>
>> vacuum_cost_page_dirty | 200 | configuration file
>>
>> vacuum_cost_page_hit | 10 | configuration file
>>
>> vacuum_cost_page_miss | 100 | configuration file
>>
>> wal_buffers | 16MB | configuration file
>>
>> wal_compression | on | configuration file
>>
>> wal_sync_method | fdatasync | configuration file
>>
>> work_mem | 1468006kB | configuration file
>>
>>
>> The part of /etc/sysctl.conf I modified is:
>>
>> vm.swappiness = 1
>>
>> vm.dirty_background_bytes = 134217728
>>
>> vm.dirty_bytes = 1073741824
>>
>> vm.overcommit_ratio = 100
>>
>> vm.zone_reclaim_mode = 0
>>
>> kernel.numa_balancing = 0
>>
>> kernel.sched_autogroup_enabled = 0
>>
>> kernel.sched_migration_cost_ns = 5000000
>>
>>
>> The problem I have is very poor read. When I benchmark my array with fio
>> I get random reads of about 200MB/s and 1100IOPS and sequential reads of
>> about 286MB/s and 21000IPS. But when I watch my queries using pg_activity,
>> I get at best 4MB/s. Also using dstat I can see that iowait time is at
>> about 25%. This problem is not query-dependent.
>>
>> I backed up the database, I reformated the array making sure it is well
>> aligned then restored the database and got the same result.
>>
>> Where should I target my troubleshooting at this stage? I reformatted my
>> drive, I tuned my postgresql.conf and OS as much as I could. The hardware
>> doesn’t seem to have any issues, I am really puzzled.
>>
>> Thanks!
>>
>>
>> Charles
>>
>> --
>> Charles Nadeau Ph.D.
>>
>
>

--
Charles Nadeau Ph.D.
http://charlesnadeau.blogspot.com/