Command #

Materialize -- [--cells=<cells>] [--tablet_types=<source_tablet_types>] <json_spec>

Description #

Materialize is a lower level vreplication command that allows for generalized materialization of tables. The target tables can be copies, aggregations, or views. The target tables are kept in sync in near-realtime.

You can specify multiple tables to materialize using the json_spec parameter.

Be careful to avoid using the INSTANT ADD COLUMN feature in MySQL 8.0+ with materialization source tables as this can cause the vreplication based materialization workflow to break.

Parameters #

--cells #

default local cell

A comma-separated list of cell names or cell aliases. This list is used by VReplication to determine which cells should be used to pick a tablet for selecting data from the source keyspace.

Uses #
  • Improve performance by using picking a tablet in cells in network proximity with the target
  • To reduce bandwidth costs by skipping cells that are in different availability zones
  • Select cells where replica lags are lower

--tablet_types #

default --vreplication_tablet_type parameter value for the tablet. --vreplication_tablet_type has the default value of "in_order:REPLICA,PRIMARY".

Source tablet types to replicate from (e.g. PRIMARY, REPLICA, RDONLY). The value specified impacts tablet selection for the workflow.

Uses #
  • To reduce the load on PRIMARY tablets by using REPLICAs or RDONLYs
  • Reducing lag by pointing to PRIMARY

JSON spec details #

  • workflow name to refer to this materialization
  • source_keyspace keyspace containing the source table
  • target_keyspace keyspace to materialize to
  • table_settings list of views to be materialized and the associated query
    • target_table name of table to which to materialize the data to
    • source_expression the materialization query
  • Optional parameters:
    • stop_after_copy if vreplication should be stopped after the copy phase is complete
    • cell name of a cell, or a comma separated list of cells, that should be used for choosing source tablet(s) for the materialization. If this parameter is not specified, only cell(s) local to the target tablet(s) is considered
    • tablet_types a Vitess tablet_type, or comma separated list of tablet types, that should be used for choosing source tablet(s) for the materialization. If not specified, this defaults to the tablet type(s) specified by the --vreplication_tablet_type VTTablet command line flag

Example #

Materialize '{"workflow": "product_sales", "source_keyspace": "commerce", "target_keyspace": "customer",
    "table_settings": [{"target_table": "sales_by_sku",
    "source_expression": "select sku, count(*), sum(price) from corder group by order_id"}],
    "cell": "zone1", "tablet_types": "REPLICA"}'

A Materialize Workflow #

Once you decide on your materialization requirements, you need to initiate a VReplication workflow as follows:

  1. Initiate the migration using Materialize
  2. Monitor the workflow using Workflow
  3. Start accessing your views once the workflow has started Replicating

Notes #

There are special commands to perform common materialization tasks and you should prefer them to using Materialize directly.

  • If you just want to copy tables to a different keyspace use MoveTables
  • If you want to change sharding strategies use Reshard instead