About microbatch incremental models beta

Microbatch

The microbatch strategy is available in beta for dbt Cloud Versionless and dbt Core v1.9. We have been developing it behind a flag to prevent unintended interactions with existing custom incremental strategies. To enable this feature, set the environment variable DBT_EXPERIMENTAL_MICROBATCH to True in your dbt Cloud environments or wherever you're running dbt Core.

Read and participate in the discussion: dbt-core#10672

What is "microbatch" in dbt?

Incremental models in dbt are a materialization designed to efficiently update your data warehouse tables by only transforming and loading new or changed data since the last run. Instead of reprocessing an entire dataset every time, incremental models process a smaller number of rows, and then append, update, or replace those rows in the existing table. This can significantly reduce the time and resources required for your data transformations.

Microbatch incremental models make it possible to process transformations on very large time-series datasets with efficiency and resiliency. When dbt runs a microbatch model — whether for the first time, during incremental runs, or in specified backfills — it will split the processing into multiple queries (or "batches"), based on the event_time and batch_size you configure.

Each "batch" corresponds to a single bounded time period (by default, a single day of data). Where other incremental strategies operate only on "old" and "new" data, microbatch models treat every batch as an atomic unit that can be built or replaced on its own. Each batch is independent and idempotent. This is a powerful abstraction that makes it possible for dbt to run batches separately — in the future, concurrently — and to retry them independently.

Example

A sessions model aggregates and enriches data that comes from two other models.

• page_views is a large, time-series table. It contains many rows, new records almost always arrive after existing ones, and existing records rarely update.
• customers is a relatively small dimensional table. Customer attributes update often, and not in a time-based manner — that is, older customers are just as likely to change column values as newer customers.

The page_view_start column in page_views is configured as that model's event_time. The customers model does not configure an event_time. Therefore, each batch of sessions will filter page_views to the equivalent time-bounded batch, and it will not filter customers (a full scan for every batch).

models/staging/page_views.yml

models:
  - name: page_views
    config:
      event_time: page_view_start

We run the sessions model on October 1, 2024, and then again on October 2. It produces the following queries:

Model definition

The event_time for the sessions model is set to session_start, which marks the beginning of a user’s session on the website. This setting allows dbt to combine multiple page views (each tracked by their own page_view_start timestamps) into a single session. This way, session_start differentiates the timing of individual page views from the broader timeframe of the entire user session.

models/sessions.sql

{{ config(
    materialized='incremental',
    incremental_strategy='microbatch',
    event_time='session_start',
    begin='2020-01-01',
    batch_size='day'
) }}

with page_views as (

    -- this ref will be auto-filtered
    select * from {{ ref('page_views') }}

),

customers as (

    -- this ref won't
    select * from {{ ref('customers') }}

),

select
  page_views.id as session_id,
  page_views.page_view_start as session_start,
  customers.*
  from page_views
  left join customers
    on page_views.customer_id = customer.id

Compiled (Oct 1, 2024)

target/compiled/sessions.sql

with page_views as (

    select * from (
        -- filtered on configured event_time
        select * from "analytics"."page_views"
        where page_view_start >= '2024-10-01 00:00:00'  -- Oct 1
        and page_view_start < '2024-10-02 00:00:00'
    )

),

customers as (

    select * from "analytics"."customers"

),

...

Compiled (Oct 2, 2024)

target/compiled/sessions.sql

with page_views as (

    select * from (
        -- filtered on configured event_time
        select * from "analytics"."page_views"
        where page_view_start >= '2024-10-02 00:00:00'  -- Oct 2
        and page_view_start < '2024-10-03 00:00:00'
    )

),

customers as (

    select * from "analytics"."customers"

),

...

dbt will instruct the data platform to take the result of each batch query and insert, update, or replace the contents of the analytics.sessions table for the same day of data. To perform this operation, dbt will use the most efficient atomic mechanism for "full batch" replacement that is available on each data platform.

It does not matter whether the table already contains data for that day. Given the same input data, the resulting table is the same no matter how many times a batch is reprocessed.

Each batch of sessions filters page_views to the matching time-bound batch, but doesn't filter sessions, performing a full scan for each batch.

Relevant configs

Several configurations are relevant to microbatch models, and some are required:

Config	Type	Description	Default
event_time	Column (required)	The column indicating "at what time did the row occur." Required for your microbatch model and any direct parents that should be filtered.	N/A
begin	Date (required)	The "beginning of time" for the microbatch model. This is the starting point for any initial or full-refresh builds. For example, a daily-grain microbatch model run on 2024-10-01 with begin = '2023-10-01 will process 366 batches (it's a leap year!) plus the batch for "today."	N/A
batch_size	String (required)	The granularity of your batches. The default is day (and currently this is the only granularity supported).	day
lookback	Integer (optional)	Process X batches prior to the latest bookmark to capture late-arriving records.	0

The event_time column configures the real-world time of this record

As a best practice, we recommend configuring full_refresh: False on microbatch models so that they ignore invocations with the --full-refresh flag. If you need to reprocess historical data, do so with a targeted backfill that specifies explicit start and end dates.

Usage

You must write your model query to process (read and return) exactly one "batch" of data. This is a simplifying assumption and a powerful one:

• You don’t need to think about is_incremental filtering
• You don't need to pick among DML strategies (upserting/merging/replacing)
• You can preview your model, and see the exact records for a given batch that will appear when that batch is processed and written to the table

When you run a microbatch model, dbt will evaluate which batches need to be loaded, break them up into a SQL query per batch, and load each one independently.

dbt will automatically filter upstream inputs (source or ref) that define event_time, based on the lookback and batch_size configs for this model.

During standard incremental runs, dbt will process batches according to the current timestamp and the configured lookback, with one query per batch.

Configure a lookback to reprocess additional batches during standard incremental runs

Note: If there’s an upstream model that configures event_time, but you don’t want the reference to it to be filtered, you can specify ref('upstream_model').render() to opt-out of auto-filtering. This isn't generally recommended — most models that configure event_time are fairly large, and if the reference is not filtered, each batch will perform a full scan of this input table.

Backfills

Whether to fix erroneous source data or retroactively apply a change in business logic, you may need to reprocess a large amount of historical data.

Backfilling a microbatch model is as simple as selecting it to run or build, and specifying a "start" and "end" for event_time. As always, dbt will process the batches between the start and end as independent queries.

dbt run --event-time-start "2024-09-01" --event-time-end "2024-09-04"

Configure a lookback to reprocess additional batches during standard incremental runs

Retry

If one or more of your batches fail, you can use dbt retry to reprocess only the failed batches.

Timezones

For now, dbt assumes that all values supplied are in UTC:

• event_time
• begin
• --event-time-start
• --event-time-end

While we may consider adding support for custom time zones in the future, we also believe that defining these values in UTC makes everyone's lives easier.

How microbatch compares to other incremental strategies?

Most incremental models rely on the end user (you) to explicitly tell dbt what "new" means, in the context of each model, by writing a filter in an {% if is_incremental() %} conditional block. You are responsible for crafting this SQL in a way that queries {{ this }} to check when the most recent record was last loaded, with an optional look-back window for late-arriving records.

Other incremental strategies will control how the data is being added into the table — whether append-only insert, delete + insert, merge, insert overwrite, etc — but they all have this in common.

As an example:

{{
    config(
        materialized='incremental',
        incremental_strategy='delete+insert',
        unique_key='date_day'
    )
}}

select * from {{ ref('stg_events') }}

    {% if is_incremental() %}
        -- this filter will only be applied on an incremental run
        -- add a lookback window of 3 days to account for late-arriving records
        where date_day >= (select {{ dbt.dateadd("day", -3, "max(date_day)") }} from {{ this }})  
    {% endif %}

For this incremental model:

• "New" records are those with a date_day greater than the maximum date_day that has previously been loaded
• The lookback window is 3 days
• When there are new records for a given date_day, the existing data for date_day is deleted and the new data is inserted

Let’s take our same example from before, and instead use the new microbatch incremental strategy:

models/staging/stg_events.sql

{{
    config(
        materialized='incremental',
        incremental_strategy='microbatch',
        event_time='event_occured_at',
        batch_size='day',
        lookback=3,
        begin='2020-01-01',
        full_refresh=false
    )
}}

select * from {{ ref('stg_events') }} -- this ref will be auto-filtered

Where you’ve also set an event_time for the model’s direct parents - in this case, stg_events:

models/staging/stg_events.yml

models:
  - name: stg_events
    config:
      event_time: my_time_field

And that’s it!

When you run the model, each batch templates a separate query. For example, if you were running the model on October 1, dbt would template separate queries for each day between September 28 and October 1, inclusive — four batches in total.

The query for 2024-10-01 would look like:

target/compiled/staging/stg_events.sql

select * from (
    select * from "analytics"."stg_events"
    where my_time_field >= '2024-10-01 00:00:00'
      and my_time_field < '2024-10-02 00:00:00'
)

Based on your data platform, dbt will choose the most efficient atomic mechanism to insert, update, or replace these four batches (2024-09-28, 2024-09-29, 2024-09-30, and 2024-10-01) in the existing table.