# Materialize v0.27
v0.27.0 is the first cloud-native release of Materialize. It contains
substantial breaking changes from [v0.26 LTS].

## v0.27.0

* Add [clusters](/sql/create-cluster) and [cluster replicas](/sql/create-cluster-replica/),
  which together allocate isolated, highly available, and horizontally scalable
  compute resources that incrementally maintain a "cluster" of indexes.

* Add [materialized views](/sql/create-materialized-view), which are views that
  are persisted in durable storage and incrementally updated as new data
  arrives.

  A materialized view is created in a
  [cluster](/concepts/clusters/) that
  is tasked with keeping its results up-to-date, but **can be referenced in any
  cluster**.

  The result of a materialized view is not maintained in memory, unless you
  create an [index](/sql/create-index) on it. However, intermediate state
  necessary for efficient incremental updates of the materialized view may be
  maintained in memory.

* Add [connections](/sql/create-connection/), which describe how to connect to
  and authenticate with external systems. Once created, a connection is reusable
  across multiple [`CREATE SOURCE`](/sql/create-source) and
  [`CREATE SINK`](/sql/create-sink) statements.

* Add [secrets](/sql/create-secret), which securely store sensitive credentials
  (like passwords and SSL keys) for reference in connections.

* Durably record data ingested from [sources](/sql/create-source).

  Once a source has acknowledged data upstream (e.g., via committing a Kafka
  offset or advancing a PostgreSQL replication slot), it will never re-read that
  data. As a result, PostgreSQL sources no longer have a "single
  materialization" limitation. All sources are directly queryable via
  [`SELECT`](/sql/select).

* Allow provisioning the size of a source or sink.

  Each source and sink now runs with an isolated set of compute resources. You
  can adjust the size of the resource allocation with the
  [`SIZE`](/sql/create-source/#sizing-a-source) parameter.

* Add [load generator sources](/sql/create-source/load-generator), which
  produce synthetic data for use in demos and performance tests.

* Add an [HTTP API](/integrations/http-api) which supports executing SQL queries
  over HTTP.

* **Breaking change.** Require all [indexes](/sql/create-index) to be associated
  with a cluster.

* **Breaking change.** Require the use of [connections](/sql/create-connection/)
  with Kafka sources, PostgreSQL sources, and Kafka sinks.

* **Breaking change.** Rename `TAIL` to [`SUBSCRIBE`](/sql/subscribe).

* **Breaking change.** Change the meaning of `CREATE MATERIALIZED VIEW`.

  `CREATE MATERIALIZED VIEW` now creates a new type of object called a
  [materialized view](/sql/create-materialized-view), rather than providing a
  shorthand for creating a view with a default index.

  To emulate the old behavior, explicitly create a default index after creating
  a view:

  ```mzsql
  CREATE VIEW <name> ...;
  CREATE DEFAULT INDEX ON <name>;
  ```

* **Breaking change.** Remove the `MATERIALIZED` option from `CREATE SOURCE`.

  `CREATE MATERIALIZED SOURCE` is no longer shorthand for creating a source with
  a default index. Instead, you must explicitly create a default index after
  creating a source:

  ```mzsql
  CREATE SOURCE <name> ...;
  CREATE DEFAULT INDEX ON <name>;
  ```

* **Breaking change.** Remove support for the following source types:

  * PubNub
  * Kinesis
  * S3


* **Breaking change.** Remove the `reuse_topic` option from
  [Kafka sinks](/sql/create-sink).

  The exactly-once semantics enabled by `reuse_topic` are now on by default.

* **Breaking change.** Remove the `consistency_topic` option from
  [Kafka sinks](/sql/create-sink).

* **Breaking change.** Do not default to the [Debezium
  envelope](/sql/create-sink/kafka/#debezium-envelope) in `CREATE SINK`. You
  must explicitly specify the envelope to use.

* **Breaking change.** Remove the `CREATE VIEWS` statement, which was used to
  separate the data in a PostgreSQL source into a single relation per upstream
  table.

  The PostgreSQL source now automatically creates a relation in Materialize
  for each upstream table.

* **Breaking change.** Overhaul the system catalog.

  The relations in the [`mz_catalog`](/sql/system-catalog/mz_catalog) schema
  have been adjusted substantially to support the above changes. Many column
  and relation names were adjusted for consistency. The resulting relations
  are now part of Materialize's stable interface.

  Relations which were not ready for stabilization were moved to a new
  [`mz_internal`](/sql/system-catalog/mz_internal) schema.

* **Breaking change.** Rename `mz_logical_timestamp()` to [`mz_now`](/sql/functions/now_and_mz_now/).

## Upgrade guide

Following are several examples of how to adapt source and view definitions
from Materialize v0.26 LTS for Materialize v0.27:

### Authenticated Kafka source

Change from:

```mzsql
CREATE SOURCE kafka_sasl
  FROM KAFKA BROKER 'broker.tld:9092' TOPIC 'top-secret' WITH (
      security_protocol = 'SASL_SSL',
      sasl_mechanisms = 'PLAIN',
      sasl_username = '<BROKER_USERNAME>',
      sasl_password = '<BROKER_PASSWORD>'
  )
  FORMAT AVRO USING CONFLUENT SCHEMA REGISTRY 'https://schema-registry.tld' WITH (
      username = '<SCHEMA_REGISTRY_USERNAME>',
      password = '<SCHEMA_REGISTRY_PASSWORD>'
  );
```

to:

```mzsql
CREATE SECRET kafka_password AS '<BROKER_PASSWORD>';
CREATE SECRET csr_password AS '<SCHEMA_REGISTRY_PASSWORD>';

CREATE CONNECTION kafka FOR KAFKA
    BROKER 'broker.tld:9092',
    SASL MECHANISMS 'PLAIN',
    SASL USERNAME 'materialize',
    SASL PASSWORD SECRET kafka_password;

CREATE CONNECTION csr
  FOR CONFLUENT SCHEMA REGISTRY
    USERNAME = '<SCHEMA_REGISTRY_USERNAME>',
    PASSWORD = SECRET csr_password;

CREATE SOURCE kafka_top_secret
  FROM KAFKA CONNECTION kafka TOPIC ('top-secret')
  FORMAT AVRO USING CONFLUENT SCHEMA REGISTRY CONNECTION csr
  WITH (SIZE = '3xsmall');
```

### Materialized view

Change from:

```mzsql
CREATE MATERIALIZED VIEW v AS SELECT ...
```

to:

```mzsql
CREATE VIEW v AS SELECT ...
CREATE DEFAULT INDEX ON v
```

### Materialized source

Change from:

```mzsql
CREATE MATERIALIZED SOURCE src ...
```

to:

```mzsql
CREATE SOURCE src ...
```

If you are performing point lookups on `src` directly, consider building an
index on `src` directly:

```
CREATE INDEX on src (lookup_col1, lookup_col2)
```

### `TAIL`

Change from:

```mzsql
COPY (TAIL t) TO STDOUT
```

to:

```mzsql
COPY (SUBSCRIBE t) TO STDOUT
```

[v0.26 LTS]: https://materialize.com/docs/lts/release-notes/#v0.26.4