Tuesday, November 6, 2012

meminfo To know detail Memory information on *nix server

Meminfo provides information about distribution and utilization of memory.  This utilization varies on architecture of server.  All fields may not be there is all server output.

$cat /proc/meminfo

MemTotal:        8062872 kB

MemFree:          927352 kB

Buffers:          225360 kB

Cached:          6142440 kB

SwapCached:            0 kB

Active:           949748 kB

Inactive:        5816904 kB

Active(anon):     330948 kB

Inactive(anon):    68100 kB

Active(file):     618800 kB

Inactive(file):  5748804 kB

Unevictable:           0 kB

Mlocked:               0 kB

SwapTotal:       4194296 kB

SwapFree:        4194296 kB

Dirty:                44 kB

Writeback:             0 kB

AnonPages:        398812 kB

Mapped:            61616 kB

Shmem:               192 kB

Slab:             253172 kB

SReclaimable:     221144 kB

SUnreclaim:        32028 kB

KernelStack:        1936 kB

PageTables:         7340 kB

NFS_Unstable:          0 kB

Bounce:                0 kB

WritebackTmp:          0 kB

CommitLimit:     8225732 kB

Committed_AS:     862100 kB

VmallocTotal:   34359738367 kB

VmallocUsed:      289592 kB

VmallocChunk:   34359440136 kB

HardwareCorrupted:     0 kB

AnonHugePages:    342016 kB

HugePages_Total:       0

HugePages_Free:        0

HugePages_Rsvd:        0

HugePages_Surp:        0

Hugepagesize:       2048 kB

DirectMap4k:       10240 kB

DirectMap2M:     8378368 kB

Here is the detail about some of important parameters

 MemTotal: Total usable RAM (i.e. physical ram minus a few reserved bits and the kernel binary code)
 MemFree:  Free RAM portioan
 Buffers:     Temporary storage for raw disk blocks
Cached:      In-memory cache for files read
SwapCached: Memory that once was swapped out, is swapped back in but still also is in the swapfile (if memory is needed it doesn't need to be swapped out AGAIN because it is already in the swapfile. This saves I/O)
 Active: Memory that has been used more recently and usually not reclaimed unless absolutely necessary.
 Inactive: Memory which has been less recently used.  It is more eligible to be reclaimed for other purposes

SwapTotal: total amount of swap space available
SwapFree: Memory which has been evicted from RAM, and is temporarily on the disk
Dirty: Memory which is waiting to get written back to the disk
Writeback: Memory which is actively being written back to the disk
AnonPages: Non-file backed pages mapped into userspace page tables
Mapped: files which have been mmaped, such as libraries
Slab: in-kernel data structures cache
SReclaimable: Part of Slab, that might be reclaimed, such as caches
SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
PageTables: Amount of memory dedicated to the lowest level of page tables.
NFS_Unstable: NFS pages sent to the server, but not yet committed to stable storage
Bounce: Memory used for block device "bounce buffers"
WritebackTmp: Memory used by FUSE for temporary writeback buffers
VmallocTotal: total size of vmalloc memory area
VmallocUsed: amount of vmalloc area which is used
VmallocChunk: largest contiguous block of vmalloc area which is free

Troubleshooting MySQL database performance

Here are some cool ways, how you can monitor the database performance of your MySQL installation.

Monitoring of any database/Application is always an iterative and continuous process. You need to check which graph is ok for your Application/Database. You need to measure which values are the signs of Alert or DR and what may cause it.

Below are the main items you can use to monitor your system:

1. MySQL error log
2.  mysqladmin processlist
3.  mysqladmin extended (absolute values)
4.  mysqladmin extended -i10 -r (relative values)
5.  mysql -e “show innodb status”
6.  OS data. vmstat/iostat

1) MySQL error log
-The error log is great source of information in case of there is any error.  Nothing should write to the error log, after the MySQL server has completed its initialization sequence, so everything written in error log after initialization should check immediately.
2) mysqladmin processlist or “SHOW FULL PROCESSLIST” command
It will return number of threads connected and running by using other statistics, but this is a good way to check how long queries that are running take. If there are some very long-running queries  the admin/Application team should be informed.

3) mysqladmin extended
It’s a client utility available with MySQL. You can monitor MySQL status using this utility. You need to check below parameter.

# Slave_running: If replication is configured on system, it will be provide slave status. This command should be executed on slave server.
#Threads_connected: The number of clients currently connected to MySQL server. This should be less than configured value (max_connection).
# Threads_running: If the database is overloaded you’ll get an increased number of queries running. That also should be less than some preset value . It is OK to have values over the limit for very short times. Then you can monitor some other values, when the Threads_running was more than the preset value and when it did not fall back in 5 seconds.

4) mysqladmin extended
The idea is that you store the performance counter value and compute the difference with the new values. The interval between the recordings should be more than 10 seconds. The following values are good candidates for checking:

* Aborted_clients: The number of clients that were aborted (because they did not properly close the connection to the MySQL server). For some applications this can be OK, but for some other applications you might want to track the value, as aborted connects may indicate some sort of application failure.
* Questions: Number of queries you get per second. Also, it’s total queries, not number per second. To get number per second, you must divide Questions by Uptime.
* Handler_*: If you want to monitor low-level database load, these are good values to track. If the value of Handler_read_rnd_next is abnormal relative to the value that you normally would expect, it may indicate some optimization or index problems. Handler_rollback will show the number of queries that have been rolled back. You might want to wish to investigate them.
* Opened_tables: Number of table cache misses. If the value is large, you probably need to increase table_cache. Typically you would want this to be less than 1 or 2 opened tables per second.
* Select_full_join: Joins performed without keys. This should be zero. This is a good way to catch development errors, as just a few such queries can degrease the system’s performance.
* Select_scan: Number of queries that performed a full table scan. In some cases these are OK but their ratio to all queries should be constant. if you have the value growing it can be a problem with the optimizer, lack of indexes or some other problem
* Slow_queries: Number of queries longer than –long-query-time or that are not using indexes. These should be a small fraction of all queries. If it grows, the system will have performance problems.
* Threads_created: This should be low. Higher values may mean that you need to increase the value of thread_cache or you have the amount of connections increasing, which also indicates a potential problem.

This statement produces a great deal of information, from which you should extract the parts in which you are interested. The first thing you need to check is: “Per second averages calculated from the last xx seconds”. InnoDB rounds stats each minute.

* Pending normal aio reads: These are InnoDB IO request queue sizes. If they are bigger than 10-20 you might have some bottleneck.
* reads/s, avg bytes/read, writes/s, fsyncs/s: These are IO statistics. Large values for reads/writes means the IO subsystem is being loaded. Proper values for these depend on your system configuration.
* Buffer pool hit rate: The hit rate also depends a lot on your application. Check your hit rate, when there are problems.
* inserts/s, updates/s, deletes/s, reads/s: These are low level row operations that InnoDB does. You might use these to check your load if it is in expected range.
The detail information this output you can get here.

6) OS Data. Good tools to see the system status are vmstat/iostat/mpstat.
#iostat will provide information about io on *nix systems.