Provided by: libmemcached-tools_0.44-1.1build1_amd64 bug


       memslap - Load testing and benchmarking tool for memcached


         memslap [options]


       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


       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.


   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

   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

       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.


       Below are some usage samples:

       memslap -s -S 5s
       memslap -s -t 2m -v 0.2 -e 0.05 -b
       memslap -s -F config -t 2m -w 40k -S 20s -o 0.2
       memslap -s -F config -t 2m -T 4 -c 128 -d 20 -P 40k
       memslap -s -F config -t 2m -d 50 -a -n 40
       memslap -s, -F config -t 2m
       memslap -s, -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

       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

       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

       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%


       (2). cache miss rate 5%


       3. cache_size=16G

       (1). cache miss rate 0%


       (2). cache miss

       rate 5%


       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

       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=,, --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 (; threads 1 and 4 handle server 1
       (; and thread 2 and 5 handle server 2 (

       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

   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:


       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.

       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

   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

       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=, 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

   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:


       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 '#'
        #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
        128 128 1
        #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
        2048 2048 1
        #cmd_type cmd_proportion
        #currently memslap only supports get and set command.
        #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
        0    0.1
        1.0 0.9

Format of output

       At the beginning, memslap displays some configuration information as follows:

       servers :
       threads count: 1
       concurrency: 16
       run time: 20s
       windows size: 10k
       set proportion: set_prop=0.10
       get proportion: get_prop=0.90

       servers : "servers"
           The servers used by memslap.

       threads count
           The number of threads memslap runs with.

           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

       Get Statistics
           Statistics information of get command

       Set Statistics
           Statistics information of set command

       Total Statistics
           Statistics information of both get and set command

           Result within a period

           Accumulated results

       Ops Total operations

       TPS Throughput, operations/second

       Net The rate of network

           How many objects canaXXt be gotten

       Min The minimum response time

       Max The maximum response time

           The average response time

           Standard deviation of response time

           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

       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

           Total get commands done

           Total set commands done

           How many objects canaXXt be gotten from server

           How many objects need to verify but canaXXt get them

           How many objects with insistent value

           How many objects are expired but we get them

           How many objects are unexpired but we canaXXt get them

           Total written bytes

           Total read bytes

           Total object bytes

           How many UDP packages are disorder

           How many UDP packages are lost

           How many times UDP time out happen

       Run time
           Total run time

       Ops Total operations

       TPS Throughput, operations/second

           The average rate of network


       -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.


       memslap -s -S 5s

       memslap -s -t 2m -v 0.2 -e 0.05 -b

       memslap -s -F config -t 2m -w 40k -S 20s -o 0.2

       memslap -s -F config -t 2m -T 4 -c 128 -d 20 -P 40k

       memslap -s -F config -t 2m -d 50 -a -n 40

       memslap -s, -F config -t 2m

       memslap -s, -F config -t 2m -p 2


       To find out more information please check: <>


       Mingqiang Zhuang <> (Schooner Technolgy) Brian Aker,


       memcached(1) libmemcached(3)

                                            2010-06-28                             MEMSLAP.POP(1)