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Old 06-27-2013, 07:29 PM   #1
NotionCommotion
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Understanding Memory Use


Hi,

I have two servers. The first is an old laptop and the second is a VPS hosted by others. The laptop used to run MySQL fine when it was running CentOS 5.8, but since I "upgraded" it to CentOS 6.4, it is slow as a dog (nothing against dogs, of course). Maybe just coincidence and had nothing to do with CentOS 6.4, but the hardware just happened to break at the same time...?

I have two objectives on this post. First, I want to better understand the concepts behind how Linux deals with Memory. Second, I want to know if I should go off and buy a new laptop and trash the old laptop (note that the laptop is being used as a server and not a desktop/gui, and I just use a laptop because it is convenient).

Can anyone look over the below and comment on any critical items that we should all be aware of, as well as any values that looks way out of place? I've noticed that my slow laptop has swap memory (because I set it up with some even though I didn't know what swap memory is. I assume it is the ability to use the harddrive to store RAM), and the VPS has none. Sounds like the VPS should have some, but I have no idea.

Thanks!



Laptop. Runs slow....
Code:
[root@server1 ~]# cat /proc/meminfo
MemTotal:        1912708 kB
MemFree:          739892 kB
Buffers:          226796 kB
Cached:           616272 kB
SwapCached:          312 kB
Active:           743636 kB
Inactive:         213100 kB
Active(anon):      69804 kB
Inactive(anon):    49100 kB
Active(file):     673832 kB
Inactive(file):   164000 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       4095992 kB
SwapFree:        4095612 kB
Dirty:                 0 kB
Writeback:             0 kB
AnonPages:        113364 kB
Mapped:            29364 kB
Shmem:              5236 kB
Slab:             175832 kB
SReclaimable:     115380 kB
SUnreclaim:        60452 kB
KernelStack:        1704 kB
PageTables:         8784 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:     5052344 kB
Committed_AS:     652208 kB
VmallocTotal:   34359738367 kB
VmallocUsed:      343544 kB
VmallocChunk:   34359377008 kB
HardwareCorrupted:     0 kB
AnonHugePages:     55296 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:        8556 kB
DirectMap2M:     2078720 kB
[root@server1 ~]#
VPS. Runs fast
Code:
[root@vps NotionCommotion]# cat /proc/meminfo
MemTotal:     12448864 kB
MemFree:      12028752 kB
Buffers:             0 kB
Cached:              0 kB
SwapCached:          0 kB
Active:              0 kB
Inactive:            0 kB
HighTotal:           0 kB
HighFree:            0 kB
LowTotal:     12448864 kB
LowFree:      12028752 kB
SwapTotal:           0 kB
SwapFree:            0 kB
Dirty:               0 kB
Writeback:           0 kB
AnonPages:           0 kB
Mapped:              0 kB
Slab:                0 kB
PageTables:          0 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
CommitLimit:         0 kB
Committed_AS:        0 kB
VmallocTotal:        0 kB
VmallocUsed:         0 kB
VmallocChunk:        0 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
Hugepagesize:     2048 kB
[root@vps NotionCommotion]#
 
Old 06-27-2013, 07:36 PM   #2
snowpine
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I can see from the numbers that RAM is irrelevant to your performance issues, since you have a substantial amount of unused RAM on both systems. There is no performance difference between using, say, 30% of your RAM vs. 40% of your RAM. It's like a bucket; either the bucket is big enough to hold the water, or it isn't.

Probably the performance difference is due to 2 factors:

1. Your laptop is old and slow; your VPS is hosted on fast, modern hardware.
2. CentOS 6.x is approximately 3.5 years newer than 5.x so it has higher hardware requirements. Three and a half years might not seem like a long time, but it represents a quadrupling in computer power according to Moore's Law.

Last edited by snowpine; 06-27-2013 at 07:40 PM.
 
Old 06-27-2013, 07:42 PM   #3
NotionCommotion
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Thanks snowpine,

Good analogy with the bucket.

I was going from 5.x to 6.x, not 4.x to 5.x, but point well taken.

That being said, I don't know what advantage that double brought other than slower performance. I better take it up with Moore.
 
Old 06-27-2013, 07:49 PM   #4
snowpine
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Whoops, fixed my post. Can't count very well these days.

My point is that every single package in RHEL 6 is different than in RHEL 5 so it might be tricky to isolate which variable is responsible for the performance. New kernel, new MySQL, etc...
 
Old 06-27-2013, 08:14 PM   #5
NotionCommotion
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So, you think it is like some conspiracy where the Man is causing software to force people to buy new hardware to stimulate the economy?

Or is it just developers are assuming that servers have a given feature, and when it doesn't exist because it is old, it the applications just go slower?
 
Old 06-27-2013, 08:21 PM   #6
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Quote:
I can see from the numbers that RAM is irrelevant to your performance issues
Also, what specific variables made you come to this conclusion? Not that I don't believe you, but I just want to learn. Thanks
 
Old 06-27-2013, 09:03 PM   #7
snowpine
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No conspiracy---it's just that your hosting company has better hardware than you do.

Here's a good introduction to Linux memory usage: http://linuxatemyram.com
 
Old 06-27-2013, 09:18 PM   #8
syg00
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What makes you think it's a memory problem (at all) ?. And what makes you think we can offer a cogent opinion on replacing hardware based on such scant information ?.
Some random comments:
- your (laptop) memory is not under stress. The "Cached" and much of the "Buffers" could be reclaimed by Linux to add to the "Free" should it be needed. It isn't.
- swap is used as as "overflow" memory in need. You haven't needed it.
- the VPS model in use (presumably container based) is lying to you. All those zeroes are rubbish. I saw a thread on LKML a while back where the devs insisted users should never need to see the real numbers exported by the host image. I never followed up on what happened there.
- not all dogs are slow - I have trouble keeping up with mine while I am riding my pushbike.

Edit:
Go here for the RHEL doco. Start with the release notes/tech notes for differences from your old release. Maybe Migration guide as well.
The deployment guide has some good info for where to look for relevant data in the system. The Performance tuning guide is likely to be less use than it might sound.

Last edited by syg00; 06-27-2013 at 09:40 PM.
 
Old 06-27-2013, 09:54 PM   #9
NotionCommotion
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Quote:
Originally Posted by syg00 View Post
What makes you think it's a memory problem (at all) ?. And what makes you think we can offer a cogent opinion on replacing hardware based on such scant information ?.
Yes please!!!

Code:
mysql> SHOW VARIABLES Info

auto_increment_increment    1
auto_increment_offset   1
autocommit  ON
automatic_sp_privileges ON
back_log    50
basedir /usr/
big_tables  OFF
binlog_cache_size   32768
binlog_direct_non_transactional_updates OFF
binlog_format   STATEMENT
bulk_insert_buffer_size 8388608
character_set_client    utf8
character_set_connection    utf8
character_set_database  latin1
character_set_filesystem    binary
character_set_results   utf8
character_set_server    latin1
character_set_system    utf8
character_sets_dir  /usr/share/mysql/charsets/
collation_connection    utf8_general_ci
collation_database  latin1_swedish_ci
collation_server    latin1_swedish_ci
completion_type 0
concurrent_insert   1
connect_timeout 10
datadir /var/lib/mysql/
date_format %Y-%m-%d
datetime_format %Y-%m-%d %H:%i:%s
default_week_format 0
delay_key_write ON
delayed_insert_limit    100
delayed_insert_timeout  300
delayed_queue_size  1000
div_precision_increment 4
engine_condition_pushdown   ON
error_count 0
event_scheduler OFF
expire_logs_days    0
flush   OFF
flush_time  0
foreign_key_checks  ON
ft_boolean_syntax   + -><()~*:""&|
ft_max_word_len 84
ft_min_word_len 4
ft_query_expansion_limit    20
ft_stopword_file    (built-in)
general_log OFF
general_log_file    /var/run/mysqld/mysqld.log
group_concat_max_len    1024
have_community_features YES
have_compress   YES
have_crypt  YES
have_csv    YES
have_dynamic_loading    YES
have_geometry   YES
have_innodb YES
have_ndbcluster NO
have_openssl    DISABLED
have_partitioning   YES
have_query_cache    YES
have_rtree_keys YES
have_ssl    DISABLED
have_symlink    DISABLED
hostname    server1.site2.com
identity    0
ignore_builtin_innodb   OFF
init_connect    
init_file   
init_slave  
innodb_adaptive_hash_index  ON
innodb_additional_mem_pool_size 1048576
innodb_autoextend_increment 8
innodb_autoinc_lock_mode    1
innodb_buffer_pool_size 8388608
innodb_checksums    ON
innodb_commit_concurrency   0
innodb_concurrency_tickets  500
innodb_data_file_path   ibdata1:10M:autoextend
innodb_data_home_dir    
innodb_doublewrite  ON
innodb_fast_shutdown    1
innodb_file_io_threads  4
innodb_file_per_table   OFF
innodb_flush_log_at_trx_commit  1
innodb_flush_method 
innodb_force_recovery   0
innodb_lock_wait_timeout    50
innodb_locks_unsafe_for_binlog  OFF
innodb_log_buffer_size  1048576
innodb_log_file_size    5242880
innodb_log_files_in_group   2
innodb_log_group_home_dir   ./
innodb_max_dirty_pages_pct  90
innodb_max_purge_lag    0
innodb_mirrored_log_groups  1
innodb_open_files   300
innodb_rollback_on_timeout  OFF
innodb_stats_method nulls_equal
innodb_stats_on_metadata    ON
innodb_support_xa   ON
innodb_sync_spin_loops  20
innodb_table_locks  ON
innodb_thread_concurrency   8
innodb_thread_sleep_delay   10000
innodb_use_legacy_cardinality_algorithm ON
insert_id   0
interactive_timeout 28800
join_buffer_size    131072
keep_files_on_create    OFF
key_buffer_size 8384512
key_cache_age_threshold 300
key_cache_block_size    1024
key_cache_division_limit    100
language    /usr/share/mysql/english/
large_files_support ON
large_page_size 0
large_pages OFF
last_insert_id  0
lc_time_names   en_US
license GPL
local_infile    ON
locked_in_memory    OFF
log OFF
log_bin OFF
log_bin_trust_function_creators OFF
log_bin_trust_routine_creators  OFF
log_error   /var/log/mysqld.log
log_output  FILE
log_queries_not_using_indexes   OFF
log_slave_updates   OFF
log_slow_queries    OFF
log_warnings    1
long_query_time 10.000000
low_priority_updates    OFF
lower_case_file_system  OFF
lower_case_table_names  0
max_allowed_packet  1048576
max_binlog_cache_size   18446744073709547520
max_binlog_size 1073741824
max_connect_errors  10
max_connections 151
max_delayed_threads 20
max_error_count 64
max_heap_table_size 16777216
max_insert_delayed_threads  20
max_join_size   18446744073709551615
max_length_for_sort_data    1024
max_long_data_size  1048576
max_prepared_stmt_count 16382
max_relay_log_size  0
max_seeks_for_key   18446744073709551615
max_sort_length 1024
max_sp_recursion_depth  0
max_tmp_tables  32
max_user_connections    0
max_write_lock_count    18446744073709551615
min_examined_row_limit  0
multi_range_count   256
myisam_data_pointer_size    6
myisam_max_sort_file_size   9223372036853727232
myisam_mmap_size    18446744073709551615
myisam_recover_options  OFF
myisam_repair_threads   1
myisam_sort_buffer_size 8388608
myisam_stats_method nulls_unequal
myisam_use_mmap OFF
net_buffer_length   16384
net_read_timeout    30
net_retry_count 10
net_write_timeout   60
new OFF
old OFF
old_alter_table OFF
old_passwords   OFF
open_files_limit    1024
optimizer_prune_level   1
optimizer_search_depth  62
optimizer_switch    index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on
pid_file    /var/run/mysqld/mysqld.pid
plugin_dir  /usr/lib64/mysql/plugin
port    3306
preload_buffer_size 32768
profiling   OFF
profiling_history_size  15
protocol_version    10
pseudo_thread_id    3
query_alloc_block_size  8192
query_cache_limit   1048576
query_cache_min_res_unit    4096
query_cache_size    0
query_cache_type    ON
query_cache_wlock_invalidate    OFF
query_prealloc_size 8192
rand_seed1  
rand_seed2  
range_alloc_block_size  4096
read_buffer_size    131072
read_only   OFF
read_rnd_buffer_size    262144
relay_log   
relay_log_index 
relay_log_info_file relay-log.info
relay_log_purge ON
relay_log_space_limit   0
report_host 
report_password 
report_port 3306
report_user 
rpl_recovery_rank   0
secure_auth OFF
secure_file_priv    
server_id   0
skip_external_locking   ON
skip_name_resolve   OFF
skip_networking OFF
skip_show_database  OFF
slave_compressed_protocol   OFF
slave_exec_mode STRICT
slave_load_tmpdir   /tmp
slave_max_allowed_packet    1073741824
slave_net_timeout   3600
slave_skip_errors   OFF
slave_transaction_retries   10
slow_launch_time    2
slow_query_log  OFF
slow_query_log_file /var/run/mysqld/mysqld-slow.log
socket  /var/lib/mysql/mysql.sock
sort_buffer_size    2097144
sql_auto_is_null    ON
sql_big_selects ON
sql_big_tables  OFF
sql_buffer_result   OFF
sql_log_bin ON
sql_log_off OFF
sql_log_update  ON
sql_low_priority_updates    OFF
sql_max_join_size   18446744073709551615
sql_mode    
sql_notes   ON
sql_quote_show_create   ON
sql_safe_updates    OFF
sql_select_limit    18446744073709551615
sql_slave_skip_counter  
sql_warnings    OFF
ssl_ca  
ssl_capath  
ssl_cert    
ssl_cipher  
ssl_key 
storage_engine  MyISAM
sync_binlog 0
sync_frm    ON
system_time_zone    PDT
table_definition_cache  256
table_lock_wait_timeout 50
table_open_cache    64
table_type  MyISAM
thread_cache_size   0
thread_handling one-thread-per-connection
thread_stack    262144
time_format %H:%i:%s
time_zone   SYSTEM
timed_mutexes   OFF
timestamp   1372254399
tmp_table_size  16777216
tmpdir  /tmp
transaction_alloc_block_size    8192
transaction_prealloc_size   4096
tx_isolation    REPEATABLE-READ
unique_checks   ON
updatable_views_with_limit  YES
version 5.1.69
version_comment Source distribution
version_compile_machine x86_64
version_compile_os  redhat-linux-gnu
wait_timeout    28800
warning_count   0

Code:
[root@server1 ~]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

innodb_strict_mode=on
sql_mode=TRADITIONAL
# sql_mode=STRICT_TRANS_TABLES,NO_ZERO_DATE,NO_ZERO_IN_DATE
character-set-server=utf8
collation-server=utf8_general_ci
log=/var/log/mysqld_all.log

[root@server1 ~]#

[root@server1 ~]# cat sysbench.txt
sysbench 0.4.12:  multi-threaded system evaluation benchmark

Running the test with following options:
Number of threads: 8

Doing OLTP test.
Running mixed OLTP test
Doing read-only test
Using Special distribution (12 iterations,  1 pct of values are returned in 75 pct cases)
Using "BEGIN" for starting transactions
Using auto_inc on the id column
Threads started!
Time limit exceeded, exiting...
(last message repeated 7 times)
Done.

OLTP test statistics:
    queries performed:
        read:                            634718
        write:                           0
        other:                           90674
        total:                           725392
    transactions:                        45337  (755.56 per sec.)
    deadlocks:                           0      (0.00 per sec.)
    read/write requests:                 634718 (10577.78 per sec.)
    other operations:                    90674  (1511.11 per sec.)

Test execution summary:
    total time:                          60.0048s
    total number of events:              45337
    total time taken by event execution: 479.4912
    per-request statistics:
         min:                                  2.04ms
         avg:                                 10.58ms
         max:                                 85.56ms
         approx.  95 percentile:              19.70ms

Threads fairness:
    events (avg/stddev):           5667.1250/42.18
    execution time (avg/stddev):   59.9364/0.00

[root@server1 ~]# df -T
Filesystem    Type   1K-blocks      Used Available Use% Mounted on
/dev/mapper/vg_server1-lv_root
              ext4    72383800   4243964  64462860   7% /
tmpfs        tmpfs      956352         0    956352   0% /dev/shm
/dev/sdb1     ext4      495844     60948    409296  13% /boot
[root@server1 ~]# cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Core(TM)2 Duo CPU     T7100  @ 1.80GHz
stepping        : 13
cpu MHz         : 800.000
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 2
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm ida dts tpr_shadow vnmi flexpriority
bogomips        : 3591.39
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Core(TM)2 Duo CPU     T7100  @ 1.80GHz
stepping        : 13
cpu MHz         : 800.000
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 1
cpu cores       : 2
apicid          : 1
initial apicid  : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm ida dts tpr_shadow vnmi flexpriority
bogomips        : 3591.39
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

[root@server1 ~]#
 
  


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