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Command line flags

The materialized binary supports the following command line flags:

Flag Default Modifies
--address-file N/A Address of all coordinating Materialize nodes
--data-directory ./mzdata Where data is persisted
--help N/A NOP—prints binary’s list of command line flags
--listen-addr Materialize node’s host and port
--process 0 This node’s ID when coordinating with other Materialize nodes
--processes 1 Number of coordinating Materialize nodes
--tls-cert N/A Path to TLS certificate file
--tls-key N/A Path to TLS private key file
--workers REQ Dataflow worker threads
-w REQ Dataflow worker threads
-v N/A Print version and exit
-vv N/A Print version and additional build information, and exit

Data directory

Upon startup materialized creates a directory where it persists metadata. By default, this directory is called mzdata and is situated in the current working directory of the materialized process. Currently, only metadata is persisted in mzdata. You can specify a different directory using the --data-directory flag. Upon start, materialized checks for an existing data directory, and will reinstall source and view definitions from it if one is found.

Worker threads

A materialized instance runs a specified number of timely dataflow worker threads. Worker threads can only be specified at startup by setting the required --workers flag, and cannot be changed without shutting down materialized and restarting. In the future, dynamically changing the number of worker threads will be possible over distributed clusters, see #2449.

How many worker threads should you run?

Adding worker threads allows Materialize to handle more throughput. Reducing worker threads consumes fewer resources, and reduces tail latencies.

In general, you should use the fewest number of worker threads that can handle your peak throughputs. This is also the most resource efficient.

You should never run Materialize in a configuration greater than n-1 workers, where n is the number of physical cores. Note that major cloud providers list the number of hyperthreaded cores (or virtual CPUs). Divide this number by two to get the number of physical cores available. The reasoning is simple: Timely Dataflow is very computationally efficient and typically uses all available computational resources. Under high throuput, you should see each worker pinning a core at 100% CPU, with no headroom for hyperthreading. One additional core is required for metadata management and coordination. Timely workers that have to fight for physical resources will only block each other.

Example: an r5d.4xlarge instance has 16 VCPUs, or 8 physical cores. The recommended worker setting on this VM is 7.

Horizontally scaled clusters

WARNING! Note that multi-node Materialize clusters are not supported by Materialize, and are not permitted in production under the free usage BSL license without a separate commercial agreement with Materialize.

--processes controls the total number of nodes in a horizontally-scaled Materialize cluster. The IP addresses of each node should be specified in a file, one per line, which is specified by the --address-file flag.

When each node is started, it must additionally be told which --process it is, from 0 to processes - 1.

You should not attempt running a horizontally-scaled Materialize cluster until you have maxed-out vertical-scaling. Multi-node clusters are not particulary efficient. An x1.32xlarge instance on AWS has 128 VCPUs, and will be superior in every way (reliability, cost, ease-of-use) to a multi-node Materialize cluster with the same total number of VCPUs. It is our performance goal that Materialize under that configuration be able to handle every conceivable streaming workload that you may wish to throw at it.

Listen address

By default, materialized binds to This means that Materialize will accept any incoming SQL connection to port 6875 from anywhere. It is the responsibility of the network firewall to limit incoming connections. If you wish to configure materialized to only listen to, e.g. localhost connections, you can set --listen-addr to localhost:6875. You can also use this to change the port that Materialize listens on from the default 6875.

TLS encryption

Materialize can use Transport Layer Security (TLS) to encrypt traffic between SQL and HTTP clients and the materialized server.


To enable TLS, you will need to supply two files, one containing a TLS certificate and one containing the corresponding private key. Point materialized at these files using the --tls-cert and --tls-key options, respectively:

$ materialized -w1 --tls-cert=server.crt --tls-key=server.key

When TLS is enabled, Materialize serves both unencrypted and encrypted traffic over the same TCP port, as specified by --listen-addr. The web UI will be served over HTTPS in addition to HTTP. Incoming SQL connections can negotiate TLS encryption at the client’s option; consult your SQL client’s documentation for details.

It is not currently possible to configure Materialize to reject unencrypted connections.

Materialize statically links against a vendored copy of OpenSSL. It does not use any SSL library that may be provided by your system. To see the version of OpenSSL used by a particular materialized binary, inquire with the -vv flag:

$ materialize -vv
materialized v0.2.3-dev (c62c988e8167875b92122719eee5709cf81cdac4)
OpenSSL 1.1.1g  21 Apr 2020
librdkafka v1.4.2

Materialize configures OpenSSL according to Mozilla’s Modern compatibility level, which requires TLS v1.3 and modern cipher suites. Using weaker cipher suites or older TLS protocol versions is not supported.

Generating TLS certificates

You can generate a self-signed certificate for development use with the openssl command-line tool:

$ openssl req -new -x509 -days 365 -nodes -text \
    -out server.crt -keyout server.key -subj "/CN=<SERVER-HOSTNAME>"

Production deployments typically should not use self-signed certificates. Acquire a certificate from a proper certificate authority (CA) instead.