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Command line flags

The materialized binary supports the following command line flags:

Flag Default Modifies
--cache-max-pending-records 1000000 Maximum number of input records buffered before flushing immediately to disk.
-D / --data-directory ./mzdata Where data is persisted

Known issue. The short form of this option was inadvertently removed in v0.7.0. It will be restored in v0.7.1.
--differential-idle-merge-effort N/A Advanced. Amount of compaction to perform when idle.
--help N/A NOP—prints binary’s list of command line flags
--disable-telemetry N/A Disables telemetry reporting.
--experimental Disabled Dangerous. Enable experimental features.
--introspection-frequency 1s The frequency at which to update introspection sources.
--listen-addr Materialize node’s host and port
-l / --logical-compaction-window 1ms The amount of historical detail to retain in arrangements
--timely-progress-mode demand Advanced. Timely progress tracking mode.
--tls-ca N/A Path to TLS certificate authority (CA)

Available only in unstable builds.

--tls-cert N/A Path to TLS certificate file
--tls-mode N/A How stringently to demand TLS authentication and encryption

Available only in unstable builds.

--tls-key N/A Path to TLS private key file
-w / --workers NCPUs / 2 Dataflow worker threads
-v / --version N/A Print version and exit
-vv N/A Print version and additional build information, and exit

If a command line flag takes an argument, you can alternatively set that flag via an environment variable named after the flag. If both the environment variable and command line flag are specified, the command line flag takes precedence.

The process for converting a flag name to an environment variable name is as follows:

  1. Convert all characters to uppercase
  2. Replace all hyphens with underscores
  3. add an MZ_ prefix.

For example, the --data-directory command line flag corresponds to the MZ_DATA_DIRECTORY environment variable.

Note that command line flags that do not take arguments, like --experimental and --disable-telemetry, do not yet have corresponding environment variables.

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 --workers flag, and cannot be changed without shutting down materialized and restarting. If --workers is not set, materialized will default to using half of the machine’s physical cores as the thread count. In the future, dynamically changing the number of worker threads will be possible over distributed clusters, see #2449.

Changed in v0.4.0: Rename the --threads flag to --workers.

Changed in v0.5.1: When unspecified, default to using half of the machine’s physical cores.

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 throughput, 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.

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.

Compaction window

The --logical-compaction-window option specifies the duration of time for which Materialize is required to maintain full historical detail in its arrangements. Note that compaction happens lazily, so Materialize may retain more historical detail than requested, but it will never retain less.

The value of the option is a duration string like 10ms (10 milliseconds) or 1min 30s (1 minute, 30 seconds). The special value off disables logical compaction and corresponds to an unboundedly large duration.

The logical compaction window ends at the current time and extends backwards in time for the configured duration. The default window is 1 millisecond.

See the Deployment section for guidance on tuning the compaction window.

Introspection sources

Changed in unstable builds: In prior versions of Materialize, this option was undocumented but available under the name --logging-granularity.

Materialize maintains several built-in sources and views in mz_catalog that describe the internal state of the dataflow execution layer, like mz_scheduling_elapsed.

The --introspection-frequency option determines the frequency at which the base sources are updated. The default frequency is 1s. To disable introspection entirely, use the special value off.

Higher frequencies provide more up-to-date introspection but increase load on the system. Lower frequencies increase staleness in exchange for decreased load. The default frequency is a good choice for most deployments.

TLS encryption

Materialize can use Transport Layer Security (TLS) to:

Available only in unstable builds: The --tls-mode and --tls-ca options.


Whether Materialize requires TLS encryption or authentication is determined by the value of the --tls-mode option:

Value Description
disable Disables TLS.

Materialize will reject HTTPS connections and SQL connections that negotiate TLS. This is the default mode if --tls-cert is not specified.
require Requires TLS encryption.

Materialize will reject HTTP connections and SQL connections that do not negotiate TLS.
verify-ca Like require, but additionally requires that clients present a certificate.

Materialize verifies that the client certificate is issued by the certificate authority (CA) specified by the --tls-ca option.
verify-full Like verify-ca, but the Common Name (CN) field of the client certificate additionally determines the user who is connecting.

For HTTPS connections, this user is taken directly from the CN field. For SQL connections, the name of the user in the connection parameters must match the name specified in the CN field.

This is the default mode if --tls-cert is specified.

In all TLS modes but disable, 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.

If the TLS mode is verify-ca or verify-full, you will additionally need to supply the path to a TLS certificate authority (CA) via the --tls-ca flag. Client certificates will be verified using this CA.

The following example demonstrates how to configure a server in verify-full mode:

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

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 Intermediate compatibility level, which requires TLS v1.2+ and recent 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.

Experimental mode

New in v0.4.0.

WARNING! If you want to use experimental mode, you should really read the section below!

Materialize offers access to experimental features through the --experimental flag. Unlike most features in Materialize, experimental features’ syntax and/or semantics can shift at any time, and there is no guarantee that future versions of Materialize will be interoperable with the experimental features.

Using experimental mode means that you are likely to lose access to all of your sources and views within Materialize and will have to recreate them and re-ingest all of your data.

Because of this volatility:

We recommend only using experimental mode to explore Materialize, i.e. absolutely never in production. If your explorations yield interesting results or things you’d like to see changed, let us know on GitHub.

Disabling experimental mode

You cannot disable experimental mode for a node. You can, however, extract your view and source definitions (SHOW CREATE VIEW, SHOW CREATE SOURCE, etc.), and then create a new node with those items.

Source cache

The --cache-max-pending-records specifies the number of input messages Materialize buffers in memory before flushing them all to disk when using cached sources. The default value is 1000000 messages. Note that Materialize will also flush buffered records every 10 minutes as well. See the Deployment section for more guidance on how to tune this parameter.


Unless disabled with --disable-telemetry, upon startup and once an hour materialized reports some anonymous telemetry data to a central server operated by If a newer version is available at startup a warning will be logged.

Information reported to Materialize:

Dataflow tuning

WARNING! The dataflow tuning parameters are not stable. Backwards-incompatible changes to the dataflow tuning parameters may be made at any time.

There are several command-line options that tune various parameters for Materialize’s underlying dataflow engine:

Using these parameters correctly requires substantial knowledge about how the underlying Timely and Differential Dataflow engines work. Typically you should only set these parameters in consultation with Materialize engineers.

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