NAME
memslap - Load testing and benchmarking tool for memcached
SYNOPSIS
memslap [options]
DESCRIPTION
memslap is a load generation and benchmark tool for memcached(1)
servers. It generates configurable workload such as threads,
concurrencies, connections, run time, overwrite, miss rate, key size,
value size, get/set proportion, expected throughput, and so on.
Furthermore, it also supports data verification, expire-time
verification, UDP, binary protocol, facebook test, replication test,
multi-get and reconnection, etc.
Memslap manages network connections like memcached with libevent. Each
thread of memslap is bound with a CPU core, all the threads don’t
communicate with each other, and there are several socket connections
in each thread. Each connection keeps key size distribution, value size
distribution, and command distribution by itself.
You can specify servers via the --servers option or via the environment
variable "MEMCACHED_SERVERS".
FEATURES
Memslap is developed to for the following purposes:
Manages network connections with libevent asynchronously.
Set both TCP and UDP up to use non-blocking IO.
Improves parallelism: higher performance in multi-threads environments.
Improves time efficiency: faster processing speed.
Generates key and value more efficiently; key size distribution and
value size distribution are configurable.
Supports get, multi-get, and set commands; command distribution is
configurable.
Supports controllable miss rate and overwrite rate.
Supports data and expire-time verification.
Supports dumping statistic information periodically.
Supports thousands of TCP connections.
Supports binary protocol.
Supports facebook test (set with TCP and multi-get with UDP) and
replication test.
DETAILS
Effective implementation of network.
For memslap, both TCP and UDP use non-blocking network IO. All the
network events are managed by libevent as memcached. The network module
of memslap is similar to memcached. Libevent can ensure memslap can
handle network very efficiently.
Effective implementation of multi-threads and concurrency
Memslap has the similar implementation of multi-threads to memcached.
Memslap creates one or more self-governed threads; each thread is bound
with one CPU core if the system supports setting CPU core affinity.
In addition, each thread has a libevent to manage the events of the
network; each thread has one or more self-governed concurrencies; and
each concurrency has one or more socket connections. All the
concurrencies donaXXt communicate with each other even though they are
in the same thread.
Memslap can create thousands of socket connections, and each
concurrency has tens of socket connections. Each concurrency randomly
or sequentially selects one socket connection from its socket
connection pool to run, so memslap can ensure each concurrency handles
one socket connection at any given time. Users can specify the number
of concurrency and socket connections of each concurrency according to
their expected workload.
Effective implementation of generating key and value
In order to improve time efficiency and space efficiency, memslap
creates a random characters table with 10M characters. All the suffixes
of keys and values are generated from this random characters table.
Memslap uses the offset in the character table and the length of the
string to identify a string. It can save much memory. Each key
contains two parts, a prefix and a suffix. The prefix is an uint64_t, 8
bytes. In order to verify the data set before, memslap need to ensure
each key is unique, so it uses the prefix to identify a key. The prefix
cannot include illegal characters, such as aXX\raXX, aXX\naXX, aXX\0aXX
and aXX aXX. And memslap has an algorithm to ensure that.
Memslap doesnaXXt generate all the objects (key-value pairs) at the
beginning. It only generates enough objects to fill the task window
(default 10K objects) of each concurrency. Each object has the
following basic information, key prefix, key suffix offset in the
character table, key length, value offset in the character table, and
value length.
In the work process, each concurrency sequentially or randomly selects
an object from the window to do set operation or get operation. At the
same time, each concurrency kicks objects out of its window and adds
new object into it.
Simple but useful task scheduling
Memslap uses libevent to schedule all the concurrencies of threads, and
each concurrency schedules tasks based on the local task window.
Memslap assumes that if each concurrency keeps the same key
distribution, value distribution and commands distribution, from
outside, memslap keeps all the distribution as a whole. Each task
window includes a lot of objects, each object stores its basic
information, such as key, value, expire time, and so on. At any time,
all the objects in the window keep the same and fixed key and value
distribution. If an object is overwritten, the value of the object will
be updated. Memslap verifies the data or expire-time according to the
object information stored in the task window.
Libevent selects which concurrency to handle based on a specific
network event. Then the concurrency selects which command (get or set)
to operate based on the command distribution. If it needs to kick out
an old object and add a new object, in order to keep the same key and
value distribution, the new object must have the same key length and
value length.
If memcached server has two cache layers (memory and SSD), running
memslap with different window sizes can get different cache miss rates.
If memslap adds enough objects into the windows at the beginning, and
the cache of memcached cannot store all the objects initialized, then
memslap will get some objects from the second cache layer. It causes
the first cache layer to miss. So the user can specify the window size
to get the expected miss rate of the first cache layer.
Useful implementation of multi-servers , UDP, TCP, multi-get and binary
protocol
Because each thread is self-governed, memslap can assign different
threads to handle different memcached servers. This is just one of the
ways in which memslap supports multiple servers. The only limitation is
that the number of servers cannot be greater than the number of
threads. The other way to support multiple servers is for replication
test. Each concurrency has one socket connection to each memcached
server. For the implementation, memslap can set some objects to one
memcached server, and get these objects from the other servers.
By default, Memslap does single get. If the user specifies multi-get
option, memslap will collect enough get commands and pack and send the
commands together.
Memslap supports both the ASCII protocol and binary protocol, but it
runs on the ASCII protocol by default. Memslap by default runs on the
TCP protocol, but it also supports UDP. Because UDP is unreliable,
dropped packages and out-of-order packages may occur. Memslap creates a
memory buffer to handle these problems. Memslap tries to read all the
response data of one command from the server and reorders the response
data. If some packages get lost, the waiting timeout mechanism can
ensure half-baked packages will be discarded and the next command will
be sent.
USAGE
Below are some usage samples:
memslap -s 127.0.0.1:11211 -S 5s
memslap -s 127.0.0.1:11211 -t 2m -v 0.2 -e 0.05 -b
memslap -s 127.0.0.1:11211 -F config -t 2m -w 40k -S 20s -o 0.2
memslap -s 127.0.0.1:11211 -F config -t 2m -T 4 -c 128 -d 20 -P 40k
memslap -s 127.0.0.1:11211 -F config -t 2m -d 50 -a -n 40
memslap -s 127.0.0.1:11211,127.0.0.1:11212 -F config -t 2m
memslap -s 127.0.0.1:11211,127.0.0.1:11212 -F config -t 2m -p 2
The user must specify one server at least to run memslap. The rest of
the parameters have default values, as shown below:
Thread number = 1 Concurrency = 16
Run time = 600 seconds Configuration file = NULL
Key size = 64 Value size = 1024
Get/set = 9:1 Window size = 10k
Execute number = 0 Single get = true
Multi-get = false Number of sockets of each
concurrency = 1
Reconnect = false Data verification = false
Expire-time verification = false ASCII protocol = true
Binary protocol = false Dumping statistic information
periodically = false
Overwrite proportion = 0% UDP = false
TCP = true Limit throughput = false
Facebook test = false Replication test = false
Key size, value size and command distribution.
All the distributions are read from the configuration file specified by
user with aXXaXXcfg_cmdaXX option. If the user does not specify a
configuration file, memslap will run with the default distribution (key
size = 64, value size = 1024, get/set = 9:1). For information on how to
edit the configuration file, refer to the aXXConfiguration FileaXX
section.
The minimum key size is 16 bytes; the maximum key size is 250 bytes.
The precision of proportion is 0.001. The proportion of distribution
will be rounded to 3 decimal places.
The minimum value size is 1 bytes; the maximum value size is 1M bytes.
The precision of proportion is 0.001. The proportion of distribution
will be rounded to 3 decimal places. Currently, memslap only supports
set and get commands. And it supports 100% set and 100% get. For 100%
get, it will preset some objects to the server.
Multi-thread and concurrency
The high performance of memslap benefits from the special schedule of
thread and concurrency. ItaXXs important to specify the proper number
of them. The default number of threads is 1; the default number of
concurrency is 16. The user can use aXXaXXthreadsaXX and
aXX--concurrencyaXX to specify these variables.
If the system supports setting CPU affinity and the number of threads
specified by the user is greater than 1, memslap will try to bind each
thread to a different CPU core. So if you want to get the best
performance memslap, it is better to specify the number of thread equal
to the number of CPU cores. The number of threads specified by the user
can also be less or greater than the number of CPU cores. Because of
the limitation of implementation, the number of concurrencies could be
the multiple of the number of threads.
1. For 8 CPU cores system
For example:
--threads=2 --concurrency=128
--threads=8 --concurrency=128
--threads=8 --concurrency=256
--threads=12 --concurrency=144
2. For 16 CPU cores system
For example:
--threads=8 --concurrency=128
--threads=16 --concurrency=256
--threads=16 --concurrency=512
--threads=24 --concurrency=288
The memslap performs very well, when used to test the performance of
memcached servers. Most of the time, the bottleneck is the network or
the server. If for some reason the user wants to limit the performance
of memslap, there are two ways to do this:
Decrease the number of threads and concurrencies. Use the option
aXX--tpsaXX that memslap provides to limit the throughput. This option
allows the user to get the expected throughput. For example, assume
that the maximum throughput is 50 kops/s for a specific configuration,
you can specify the throughput equal to or less than the maximum
throughput using aXX--tpsaXX option.
Window size
Most of the time, the user does not need to specify the window size.
The default window size is 10k. For Schooner Memcached, the user can
specify different window sizes to get different cache miss rates based
on the test case. Memslap supports cache miss rate between 0% and 100%.
If you use this utility to test the performance of Schooner Memcached,
you can specify a proper window size to get the expected cache miss
rate. The formula for calculating window size is as follows:
Assume that the key size is 128 bytes, and the value size is 2048
bytes, and concurrency=128.
1. Small cache cache_size=1M, 100% cache miss (all data get from SSD).
win_size=10k
2. cache_size=4G
(1). cache miss rate 0%
win_size=8k
(2). cache miss rate 5%
win_size=11k
3. cache_size=16G
(1). cache miss rate 0%
win_size=32k
(2). cache miss
rate 5%
win_size=46k
The formula for calculating window size for cache miss rate 0%:
cache_size / concurrency / (key_size + value_size) * 0.5
The formula for calculating window size for cache miss rate 5%:
cache_size / concurrency / (key_size + value_size) * 0.7
Verification
Memslap supports both data verification and expire-time verification.
The user can use "--verify=" or "-v" to specify the proportion of data
verification. In theory, it supports 100% data verification. The user
can use "--exp_verify=" or "-e" to specify the proportion of expire-
time verification. In theory, it supports 100% expire-time
verification. Specify the "--verbose" options to get more detailed
error information.
For example: --exp_verify=0.01 aXXverify=0.1 , it means that 1% of the
objects set with expire-time, 10% of the objects gotten will be
verified. If the objects are gotten, memslap will verify the expire-
time and value.
multi-servers and multi-clients
Memslap supports multi-servers based on self-governed thread. There is
a limitation that the number of servers cannot be greater than the
number of threads. Memslap assigns one thread to handle one server at
least. The user can use the "--servers=" or "-s" option to specify
multi-servers.
For example:
--servers=10.1.1.1:11211,10.1.1.2:11212,10.1.1.3:11213 --threads=6
--concurrency=36
The above command means that there are 6 threads, with each thread
having 6 concurrencies and that threads 0 and 3 handle server 0
(10.1.1.1); threads 1 and 4 handle server 1 (10.1.1.2); and thread 2
and 5 handle server 2 (10.1.1.3).
All the threads and concurrencies in memslap are self-governed.
So is memslap. The user can start up several memslap instances. The
user can run memslap on different client machines to communicate with
the same memcached server at the same. It is recommended that the user
start different memslap on different machines using the same
configuration.
Run with execute number mode or time mode
The default memslap runs with time mode. The default run time is 10
minutes. If it times out, memslap will exit. Do not specify both
execute number mode and time mode at the same time; just specify one
instead.
For example:
--time=30s (It means the test will run 30 seconds.)
--execute_number=100000 (It means that after running 100000 commands,
the test will exit.)
Dump statistic information periodically.
The user can use "--stat_freq=" or "-S" to specify the frequency.
For example:
--stat_freq=20s
Memslap will dump the statistics of the commands (get and set) at the
frequency of every 20 seconds.
For more information on the format of dumping statistic information,
refer to aXXFormat of OutputaXX section.
Multi-get
The user can use "--division=" or "-d" to specify multi-get keys count.
Memslap by default does single get with TCP. Memslap also supports data
verification and expire-time verification for multi-get.
Memslap supports multi-get with both TCP and UDP. Because of the
different implementation of the ASCII protocol and binary protocol,
there are some differences between the two. For the ASCII protocol,
memslap sends one aXXmulti-getaXX to the server once. For the binary
protocol, memslap sends several single get commands together as
aXXmulti-getaXX to the server.
UDP and TCP
Memslap supports both UDP and TCP. For TCP, memslap does not reconnect
the memcached server if socket connections are lost. If all the socket
connections are lost or memcached server crashes, memslap will exit. If
the user specifies the aXX--reconnectaXX option when socket connections
are lost, it will reconnect them.
User can use aXX--udpaXX to enable the UDP feature, but UDP comes with
some limitations:
UDP cannot set data more than 1400 bytes.
UDP is not supported by the binary protocol because the binary protocol
of memcached does not support that.
UDP doesnaXXt support reconnection.
Facebook test
Set data with TCP and multi-get with UDP. Specify the following
options:
"--facebook --division=50"
If you want to create thousands of TCP connections, specify the
"--conn_sock=" option.
For example: --facebook --division=50 --conn_sock=200
The above command means that memslap will do facebook test, each
concurrency has 200 socket TCP connections and one UDP socket.
Memslap sets objects with the TCP socket, and multi-gets 50 objects
once with the UDP socket.
If you specify "--division=50", the key size must be less that 25 bytes
because the UDP packet size is 1400 bytes.
Replication test
For replication test, the user must specify at least two memcached
servers. The user can use aXXaXXrep_write=aXX option to enable
feature.
For example:
--servers=10.1.1.1:11211,10.1.1.2:11212 aXXrep_write=2
The above command means that there are 2 replication memcached servers,
memslap will set objects to both server 0 and server 1, get objects
which are set to server 0 before from server 1, and also get objects
which are set to server 1 before from server 0. If server 0 crashes,
memslap will only get objects from server 1. If server 0 comes back to
life again, memslap will reconnect server 0. If both server 0 and
server 1 crash, memslap will exit.
Supports thousands of TCP connections
Start memslap with "--conn_sock=" or "-n" to enable this feature. Make
sure that your system can support opening thousands of files and
creating thousands of sockets. However, this feature does not support
reconnection if sockets disconnect.
For example:
--threads=8 --concurrency=128 --conn_sock=128
The above command means that memslap starts up 8 threads, each thread
has 16 concurrencies, each concurrency has 128 TCP socket connections,
and the total number of TCP socket connections is 128 * 128 = 16384.
Supports binary protocol
Start memslap with "--binary" or "-B" options to enable this feature.
It supports all the above features except UDP, because the latest
memcached 1.3.3 does not implement binary UDP protocol.
For example:
--binary
Since memcached 1.3.3 doesn’t implement binary UDP protocol, memslap
does not support UDP. In addition, memcached 1.3.3 does not support
multi-get. If you specify "--division=50" option, it just sends 50 get
commands together as aXXmulit-getaXX to the server.
Configuration file
This section describes the format of the configuration file. By
default when no configuration file is specified memslap reads the
default one located at ~/.memslap.cnf.
Below is a sample configuration file:
***************************************************************************
#comments should start with '#'
#key
#start_len end_len proportion
#
#key length range from start_len to end_len
#start_len must be equal to or greater than 16
#end_len must be equal to or less than 250
#start_len must be equal to or greater than end_len
#memslap will generate keys according to the key range
#proportion: indicates keys generated from one range accounts for the total
generated keys
#
#example1: key range 16~100 accounts for 80%
# key range 101~200 accounts for 10%
# key range 201~250 accounts for 10%
# total should be 1 (0.8+0.1+0.1 = 1)
#
# 16 100 0.8
# 101 200 0.1
# 201 249 0.1
#
#example2: all keys length are 128 bytes
#
# 128 128 1
key
128 128 1
#value
#start_len end_len proportion
#
#value length range from start_len to end_len
#start_len must be equal to or greater than 1
#end_len must be equal to or less than 1M
#start_len must be equal to or greater than end_len
#memslap will generate values according to the value range
#proportion: indicates values generated from one range accounts for the
total generated values
#
#example1: value range 1~1000 accounts for 80%
# value range 1001~10000 accounts for 10%
# value range 10001~100000 accounts for 10%
# total should be 1 (0.8+0.1+0.1 = 1)
#
# 1 1000 0.8
# 1001 10000 0.1
# 10001 100000 0.1
#
#example2: all value length are 128 bytes
#
# 128 128 1
value
2048 2048 1
#cmd
#cmd_type cmd_proportion
#
#currently memslap only supports get and set command.
#
#cmd_type
#set 0
#get 1
#
#example: set command accounts for 50%
# get command accounts for 50%
# total should be 1 (0.5+0.5 = 1)
#
# cmd
# 0 0.5
# 1 0.5
cmd
0 0.1
1.0 0.9
Format of output
At the beginning, memslap displays some configuration information as
follows:
servers : 127.0.0.1:11211
threads count: 1
concurrency: 16
run time: 20s
windows size: 10k
set proportion: set_prop=0.10
get proportion: get_prop=0.90
Where
servers : "servers"
The servers used by memslap.
threads count
The number of threads memslap runs with.
concurrency
The number of concurrencies memslap runs with.
run time
How long to run memslap.
windows size
The task window size of each concurrency.
set proportion
The proportion of set command.
get proportion
The proportion of get command.
The output of dynamic statistics is something like this:
---------------------------------------------------------------------------------------------------------------------------------
Get Statistics
Type Time(s) Ops TPS(ops/s) Net(M/s) Get_miss Min(us) Max(us)
Avg(us) Std_dev Geo_dist
Period 5 345826 69165 65.3 0 27 2198 203
95.43 177.29
Global 20 1257935 62896 71.8 0 26 3791 224
117.79 192.60
Set Statistics
Type Time(s) Ops TPS(ops/s) Net(M/s) Get_miss Min(us) Max(us)
Avg(us) Std_dev Geo_dist
Period 5 38425 7685 7.3 0 42 628 240
88.05 220.21
Global 20 139780 6989 8.0 0 37 3790 253
117.93 224.83
Total Statistics
Type Time(s) Ops TPS(ops/s) Net(M/s) Get_miss Min(us) Max(us)
Avg(us) Std_dev Geo_dist
Period 5 384252 76850 72.5 0 27 2198 207
94.72 181.18
Global 20 1397720 69886 79.7 0 26 3791 227
117.93 195.60
---------------------------------------------------------------------------------------------------------------------------------
Where
Get Statistics
Statistics information of get command
Set Statistics
Statistics information of set command
Total Statistics
Statistics information of both get and set command
Period
Result within a period
Global
Accumulated results
Ops Total operations
TPS Throughput, operations/second
Net The rate of network
Get_miss
How many objects canaXXt be gotten
Min The minimum response time
Max The maximum response time
Avg:
The average response time
Std_dev
Standard deviation of response time
Geo_dist
Geometric distribution based on natural exponential function
At the end, memslap will output something like this:
---------------------------------------------------------------------------------------------------------------------------------
Get Statistics (1257956 events)
Min: 26
Max: 3791
Avg: 224
Geo: 192.60
Std: 116.23
Log2 Dist:
4: 0 10 84490 215345
8: 484890 459823 12543 824
12: 31
Set Statistics (139782 events)
Min: 37
Max: 3790
Avg: 253
Geo: 224.84
Std: 116.83
Log2 Dist:
4: 0 0 4200 16988
8: 50784 65574 2064 167
12: 5
Total Statistics (1397738 events)
Min: 26
Max: 3791
Avg: 227
Geo: 195.60
Std: 116.60
Log2 Dist:
4: 0 10 88690 232333
8: 535674 525397 14607 991
12: 36
cmd_get: 1257969
cmd_set: 139785
get_misses: 0
verify_misses: 0
verify_failed: 0
expired_get: 0
unexpired_unget: 0
written_bytes: 242516030
read_bytes: 1003702556
object_bytes: 152086080
packet_disorder: 0
packet_drop: 0
udp_timeout: 0
Run time: 20.0s Ops: 1397754 TPS: 69817 Net_rate: 59.4M/s
---------------------------------------------------------------------------------------------------------------------------------
Where
Get Statistics
Get statistics of response time
Set Statistics
Set statistics of response time
Total Statistics
Both get and set statistics of response time
Min The accumulated and minimum response time
Max The accumulated and maximum response time
Avg The accumulated and average response time
Std Standard deviation of response time
Log2 Dist
Geometric distribution based on logarithm 2
cmd_get
Total get commands done
cmd_set
Total set commands done
get_misses
How many objects canaXXt be gotten from server
verify_misses
How many objects need to verify but canaXXt get them
verify_failed
How many objects with insistent value
expired_get
How many objects are expired but we get them
unexpired_unget
How many objects are unexpired but we canaXXt get them
written_bytes
Total written bytes
read_bytes
Total read bytes
object_bytes
Total object bytes
packet_disorder
How many UDP packages are disorder
packet_drop
How many UDP packages are lost
udp_timeout
How many times UDP time out happen
Run time
Total run time
Ops Total operations
TPS Throughput, operations/second
Net_rate
The average rate of network
OPTIONS
-s, --servers=
List one or more servers to connect. Servers count must be less
than
threads count. e.g.: --servers=localhost:1234,localhost:11211
-T, --threads=
Number of threads to startup, better equal to CPU numbers. Default
8.
-c, --concurrency=
Number of concurrency to simulate with load. Default 128.
-n, --conn_sock=
Number of TCP socks per concurrency. Default 1.
-x, --execute_number=
Number of operations(get and set) to execute for the
given test. Default 1000000.
-t, --time=
How long the test to run, suffix: s-seconds, m-minutes, h-hours,
d-days e.g.: --time=2h.
-F, --cfg_cmd=
Load the configure file to get command,key and value distribution
list.
-w, --win_size=
Task window size of each concurrency, suffix: K, M e.g.:
--win_size=10k.
Default 10k.
-X, --fixed_size=
Fixed length of value.
-v, --verify=
The proportion of date verification, e.g.: --verify=0.01
-d, --division=
Number of keys to multi-get once. Default 1, means single get.
-S, --stat_freq=
Frequency of dumping statistic information. suffix: s-seconds,
m-minutes, e.g.: --resp_freq=10s.
-e, --exp_verify=
The proportion of objects with expire time, e.g.:
--exp_verify=0.01.
Default no object with expire time
-o, --overwrite=
The proportion of objects need overwrite, e.g.: --overwrite=0.01.
Default never overwrite object.
-R, --reconnect
Reconnect support, when connection is closed it will be
reconnected.
-U, --udp
UDP support, default memslap uses TCP, TCP port and UDP port of
server must be same.
-a, --facebook
Whether it enables facebook test feature, set with TCP and multi-
get with UDP.
-B, --binary
Whether it enables binary protocol. Default with ASCII protocol.
-P, --tps=
Expected throughput, suffix: K, e.g.: --tps=10k.
-p, --rep_write=
The first nth servers can write data, e.g.: --rep_write=2.
-b, --verbose
Whether it outputs detailed information when verification fails.
-h, --help
Display this message and then exit.
-V, --version
Display the version of the application and then exit.
EXAMPLES
memslap -s 127.0.0.1:11211 -S 5s
memslap -s 127.0.0.1:11211 -t 2m -v 0.2 -e 0.05 -b
memslap -s 127.0.0.1:11211 -F config -t 2m -w 40k -S 20s -o 0.2
memslap -s 127.0.0.1:11211 -F config -t 2m -T 4 -c 128 -d 20 -P 40k
memslap -s 127.0.0.1:11211 -F config -t 2m -d 50 -a -n 40
memslap -s 127.0.0.1:11211,127.0.0.1:11212 -F config -t 2m
memslap -s 127.0.0.1:11211,127.0.0.1:11212 -F config -t 2m -p 2
HOME
To find out more information please check:
<http://launchpad.org/libmemcached>
AUTHORS
Mingqiang Zhuang <mingqiangzhuang@hengtiansoft.com> (Schooner
Technolgy) Brian Aker, <brian@tangent.org>
SEE ALSO
memcached(1) libmemcached(3)
2010-01-14 MEMSLAP.POP(1)