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MEMASLAP(1) libmemcached MEMASLAP(1)

NAME
memaslap - libmemcached Documentation

SYNOPSIS
memaslap [options]

--help

DESCRIPTION
memaslap is a load generation and benchmark tool for memcached servers.
It generates configurable workload such as threads, concurrencies, con‐
nections, run time, overwrite, miss rate, key size, value size, get/set
proportion, expected throughput, and so on. Furthermore, it also testss
data verification, expire-time verification, UDP, binary protocol,
facebook test, replication test, multi-get and reconnection, etc.

Memaslap manages network connections like memcached with libevent. Each
thread of memaslap is bound with a CPU core, all the threads don't com‐
municate 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 con‐
figurable.

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 repli‐
cation test.

DETAILS
Effective implementation of network.
For memaslap, both TCP and UDP use non-blocking network IO. All the
network events are managed by libevent as memcached. The network module
of memaslap is similar to memcached. Libevent can ensure memaslap 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 testss 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 concurren‐
cies don’t communicate with each other even though they are in the same
thread.

Memslap can create thousands of socket connections, and each concur‐
rency has tens of socket connections. Each concurrency randomly or
sequentially selects one socket connection from its socket connection
pool to run, so memaslap can ensure each concurrency handles one socket
connection at any given time. Users can specify the number of concur‐
rency 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, memaslap cre‐
ates 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 con‐
tains two parts, a prefix and a suffix. The prefix is an uint64_t, 8
bytes. In order to verify the data set before, memaslap need to ensure
each key is unique, so it uses the prefix to identify a key. The prefix
cannot include illegal characters, such as ‘r’, ‘n’, ‘0’ and ‘ ‘. And
memaslap has an algorithm to ensure that.

Memslap doesn’t 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 follow‐
ing 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. Mem‐
slap assumes that if each concurrency keeps the same key distribution,
value distribution and commands distribution, from outside, memaslap
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 win‐
dow 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 net‐
work 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
memaslap with different window sizes can get different cache miss
rates. If memaslap adds enough objects into the windows at the begin‐
ning, and the cache of memcached cannot store all the objects initial‐
ized, then memaslap 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, memaslap can assign different
threads to handle different memcached servers. This is just one of the
ways in which memaslap tests multiple servers. The only limitation is
that the number of servers cannot be greater than the number of
threads. The other way to test multiple servers is for replication
test. Each concurrency has one socket connection to each memcached
server. For the implementation, memaslap 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, memaslap will collect enough get commands and pack and send the
commands together.

Memslap testss 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 tests 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:

memaslap -s 127.0.0.1:11211 -S 5s

memaslap -s 127.0.0.1:11211 -t 2m -v 0.2 -e 0.05 -b

memaslap -s 127.0.0.1:11211 -F config -t 2m -w 40k -S 20s -o 0.2

memaslap -s 127.0.0.1:11211 -F config -t 2m -T 4 -c 128 -d 20 -P 40k

memaslap -s 127.0.0.1:11211 -F config -t 2m -d 50 -a -n 40

memaslap -s 127.0.0.1:11211,127.0.0.1:11212 -F config -t 2m

memaslap -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 memaslap. 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 con‐
currency = 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 “—cfg_cmd” option. If the user does not specify a configura‐
tion file, memaslap 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 “Configuration File” 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, memaslap only testss
set and get commands. And it testss 100% set and 100% get. For 100%
get, it will preset some objects to the server.

Multi-thread and concurrency
The high performance of memaslap benefits from the special schedule of
thread and concurrency. It’s important to specify the proper number of
them. The default number of threads is 1; the default number of concur‐
rency is 16. The user can use “—threads” and “--concurrency” to specify
these variables.

If the system tests setting CPU affinity and the number of threads
specified by the user is greater than 1, memaslap will try to bind each
thread to a different CPU core. So if you want to get the best perfor‐
mance memaslap, 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 memaslap 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 memaslap, there are two ways to do this:

Decrease the number of threads and concurrencies. Use the option
“--tps” that memaslap 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 “--tps” 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 testss 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 testss both data verification and expire-time verification. The
user can use "--verify=" or "-v" to specify the proportion of data ver‐
ification. In theory, it testss 100% data verification. The user can
use "--exp_verify=" or "-e" to specify the proportion of expire-time
verification. In theory, it testss 100% expire-time verification. Spec‐
ify the "--verbose" options to get more detailed error information.

For example: --exp_verify=0.01 –verify=0.1 , it means that 1% of the
objects set with expire-time, 10% of the objects gotten will be veri‐
fied. If the objects are gotten, memaslap will verify the expire-time
and value.

multi-servers and multi-config
Memslap testss 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 hav‐
ing 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 memaslap are self-governed.

So is memaslap. The user can start up several memaslap instances. The
user can run memaslap on different client machines to communicate with
the same memcached server at the same. It is recommended that the user
start different memaslap on different machines using the same configu‐
ration.

Run with execute number mode or time mode
The default memaslap runs with time mode. The default run time is 10
minutes. If it times out, memaslap will exit. Do not specify both exe‐
cute 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 “Format of Output” 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 testss data
verification and expire-time verification for multi-get.

Memslap testss multi-get with both TCP and UDP. Because of the differ‐
ent implementation of the ASCII protocol and binary protocol, there are
some differences between the two. For the ASCII protocol, memaslap
sends one “multi-get” to the server once. For the binary protocol,
memaslap sends several single get commands together as “multi-get” to
the server.

UDP and TCP
Memslap testss both UDP and TCP. For TCP, memaslap does not reconnect
the memcached server if socket connections are lost. If all the socket
connections are lost or memcached server crashes, memaslap will exit.
If the user specifies the “--reconnect” option when socket connections
are lost, it will reconnect them.

User can use “--udp” to enable the UDP feature, but UDP comes with some
limitations:

UDP cannot set data more than 1400 bytes.

UDP is not testsed by the binary protocol because the binary protocol
of memcached does not tests that.

UDP doesn’t tests 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 memaslap will do facebook test, each con‐
currency 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 “—rep_write=” option to enable feature.

For example:

--servers=10.1.1.1:11211,10.1.1.2:11212 –rep_write=2

The above command means that there are 2 replication memcached servers,
memaslap 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,
memaslap will only get objects from server 1. If server 0 comes back to
life again, memaslap will reconnect server 0. If both server 0 and
server 1 crash, memaslap will exit.

Supports thousands of TCP connections
Start memaslap with "--conn_sock=" or "-n" to enable this feature. Make
sure that your system can tests opening thousands of files and creating
thousands of sockets. However, this feature does not tests reconnection
if sockets disconnect.

For example:

--threads=8 --concurrency=128 --conn_sock=128

The above command means that memaslap 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 memaslap with "--binary" or "-B" options to enable this feature.
It testss all the above features except UDP, because the latest mem‐
cached 1.3.3 does not implement binary UDP protocol.

For example:

--binary

Since memcached 1.3.3 doesn't implement binary UDP protocol, memaslap
does not tests UDP. In addition, memcached 1.3.3 does not tests
multi-get. If you specify "--division=50" option, it just sends 50 get
commands together as “mulit-get” to the server.

CONFIGURATION FILE
This section describes the format of the configuration file. By
default when no configuration file is specified memaslap reads the
default one located at ~/.memaslap.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
#memaslap 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
#memaslap 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 memaslap only testss 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, memaslap 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 memaslap.

threads count
The number of threads memaslap runs with.

concurrency
The number of concurrencies memaslap runs with.

run time
How long to run memaslap.

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 can’t 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, memaslap 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 can’t be gotten from server

verify_misses
How many objects need to verify but can’t 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 can’t 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,local‐
host: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 distribu‐
tion 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_ver‐
ify=0.01. Default no object with expire time

-o, --overwrite=
The proportion of objects need overwrite, e.g.: --over‐
write=0.01. Default never overwrite object.

-R, --reconnect
Reconnect tests, when connection is closed it will be recon‐
nected.

-U, --udp
UDP tests, default memaslap 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
memaslap -s 127.0.0.1:11211 -S 5s

memaslap -s 127.0.0.1:11211 -t 2m -v 0.2 -e 0.05 -b

memaslap -s 127.0.0.1:11211 -F config -t 2m -w 40k -S 20s -o 0.2

memaslap -s 127.0.0.1:11211 -F config -t 2m -T 4 -c 128 -d 20 -P 40k

memaslap -s 127.0.0.1:11211 -F config -t 2m -d 50 -a -n 40

memaslap -s 127.0.0.1:11211,127.0.0.1:11212 -F config -t 2m

memaslap -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://libmemcached.org/

AUTHORS
Mingqiang Zhuang <mingqiangzhuang@hengtiansoft.com> (Schooner Tech‐
nolgy) Brian Aker, <brian@tangent.org>