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If you are interested in learning more about <strong>DataHub Cloud Observe</strong> or trying it out, please <a href="https://datahub.com/products/data-observability/" target="_blank" rel="noopener noreferrer">visit our website</a>.</p></blockquote><h2 class="anchor anchorWithStickyNavbar_LWe7" id="introduction">Introduction<a href="#introduction" class="hash-link" aria-label="Direct link to Introduction" title="Direct link to Introduction"></a></h2><p>Can you remember a time when columns were unexpectedly added, removed, or altered for a key Table in your Data Warehouse?
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Perhaps this caused downstream tables, views, dashboards, data pipelines, or AI models to break.</p><p>There are many reasons why the structure of an important Table on Snowflake, Redshift, or BigQuery may schema change, breaking the expectations
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of downstream consumers of the table.</p><p>What if you could reduce the time to detect these incidents, so that the people responsible for the data were made aware of data
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issues <em>before</em> anyone else? With DataHub Cloud <strong>Schema Assertions</strong>, you can.</p><p>DataHub Cloud allows users to define expectations about a table's columns and their data types, and will monitor and validate these expectations over
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time, notifying you when a breaking change occurs.</p><p>In this article, we'll cover the basics of monitoring Schema Assertions - what they are, how to configure them, and more - so that you and your team can
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start building trust in your most important data assets.</p><p>Let's get started!</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="support">Support<a href="#support" class="hash-link" aria-label="Direct link to Support" title="Direct link to Support"></a></h2><p>Schema Assertions are currently supported for all data sources that provide a schema via the normal ingestion process.</p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="what-is-a-schema-assertion">What is a Schema Assertion?<a href="#what-is-a-schema-assertion" class="hash-link" aria-label="Direct link to What is a Schema Assertion?" title="Direct link to What is a Schema Assertion?"></a></h2><p>A <strong>Schema Assertion</strong> is a Data Quality rule used to monitor the columns in a particular table and their data types.
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They allow you to define a set of "required" columns for the table along with their expected types, and then be notified
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if anything changes via a failing assertion.</p><p>This type of assertion can be particularly useful if you want to monitor the structure of a table which is outside of your
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direct control, for example the result of an ETL process from an upstream application or tables provided by a 3rd party data vendor. It
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allows you to get ahead of potentially breaking schema changes, by alerting you as soon as they occur, and before
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they have a chance to negatively impact downstream assets.</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="anatomy-of-a-schema-assertion">Anatomy of a Schema Assertion<a href="#anatomy-of-a-schema-assertion" class="hash-link" aria-label="Direct link to Anatomy of a Schema Assertion" title="Direct link to Anatomy of a Schema Assertion"></a></h3><p>At the most basic level, <strong>Schema Assertions</strong> consist of a few important parts:</p><ol><li>A <strong>Condition Type</strong></li><li>A set of <strong>Expected Columns</strong></li></ol><p>In this section, we'll give an overview of each.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="1-condition-type">1. Condition Type<a href="#1-condition-type" class="hash-link" aria-label="Direct link to 1. Condition Type" title="Direct link to 1. Condition Type"></a></h4><p>The <strong>Condition Type</strong> defines the conditions under which the Assertion will <strong>fail</strong>. More concretely, it determines
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how the <em>expected</em> columns should be compared to the <em>actual</em> columns found in the schema to determine a passing or failing
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state for the data quality check.</p><p>The list of supported condition types:</p><ul><li><strong>Contains</strong>: The assertion will fail if the actual schema does not contain all expected columns and their types.</li><li><strong>Exact Match</strong>: The assertion will fail if the actual schema does not EXACTLY match the expected columns and their types. No
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additional columns will be permitted.</li></ul><p>Schema Assertions will be evaluated whenever a change in the schema of the underlying table is detected.
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They also have an off switch: they can be started or stopped at any time by pressing the start (play) or stop (pause) buttons.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="2-expected-columns">2. Expected Columns<a href="#2-expected-columns" class="hash-link" aria-label="Direct link to 2. Expected Columns" title="Direct link to 2. Expected Columns"></a></h4><p>The <strong>Expected Columns</strong> are a set of column <strong>names</strong> along with their high-level <strong>data
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types</strong> that should be used to compare against the <em>actual</em> columns found in the table. By default, the expected column
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set will be derived from the current set of columns found in the table. This conveniently allows you to "freeze" or "lock"
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the current schema of a table in just a few clicks.</p><p>Each "expected column" is composed of a</p><ol><li><p><strong>Name</strong>: The name of the column that should be present in the table. Nested columns are supported in a flattened
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fashion by simply providing a dot-separated path to the nested column. For example, <code>user.id</code> would be a nested column <code>id</code>.
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In the case of a complex array or map, each field in the elements of the array or map will be treated as dot-delimited columns.
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Note that verifying the specific type of object in primitive arrays or maps is not currently supported. Note that the comparison performed
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is currently not case-sensitive.</p></li><li><p><strong>Type</strong>: The high-level data type of the column in the table. This type intentionally "high level" to allow for normal column widening practices
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without the risk of failing the assertion unnecessarily. For example a <code>varchar(64)</code> and a <code>varchar(256)</code> will both resolve to the same high-level
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"STRING" type. The currently supported set of data types include the following:</p><ul><li>String</li><li>Number</li><li>Boolean</li><li>Date</li><li>Timestamp</li><li>Struct</li><li>Array</li><li>Map</li><li>Union</li><li>Bytes</li><li>Enum</li></ul></li></ol><h2 class="anchor anchorWithStickyNavbar_LWe7" id="creating-a-schema-assertion">Creating a Schema Assertion<a href="#creating-a-schema-assertion" class="hash-link" aria-label="Direct link to Creating a Schema Assertion" title="Direct link to Creating a Schema Assertion"></a></h2><h3 class="anchor anchorWithStickyNavbar_LWe7" id="prerequisites">Prerequisites<a href="#prerequisites" class="hash-link" aria-label="Direct link to Prerequisites" title="Direct link to Prerequisites"></a></h3><ul><li><strong>Permissions</strong>: To create or delete Schema Assertions for a specific entity on DataHub, you'll need to be granted the
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<code>Edit Assertions</code>, <code>Edit Monitors</code> privileges for the entity. This will be granted to Entity owners as part of the <code>Asset Owners - Metadata Policy</code>
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by default.</li></ul><p>Once these are in place, you're ready to create your Schema Assertions!</p><h3 class="anchor anchorWithStickyNavbar_LWe7" id="steps">Steps<a href="#steps" class="hash-link" aria-label="Direct link to Steps" title="Direct link to Steps"></a></h3><ol><li>Navigate to the Table you want to monitor</li><li>Click the <strong>Quality</strong> tab</li></ol><p align="left"><img loading="lazy" width="80%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/freshness/profile-validation-tab.png" class="img_ev3q"></p><ol start="3"><li>Click <strong>+ Create Assertion</strong></li></ol><p align="left"><img loading="lazy" width="45%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/schema/assertion-builder-choose-type.png" class="img_ev3q"></p><ol start="4"><li><p>Choose <strong>Schema</strong></p></li><li><p>Select the <strong>condition type</strong>.</p></li><li><p>Define the <strong>expected columns</strong> that will be continually compared against the actual column set. This defaults to the current columns for the table.</p></li></ol><p align="left"><img loading="lazy" width="40%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/schema/assertion-builder-config.png" class="img_ev3q"></p><ol start="7"><li>Configure actions that should be taken when the assertion passes or fails</li></ol><p align="left"><img loading="lazy" width="40%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/shared/assertion-builder-actions.png" class="img_ev3q"></p><ul><li><p><strong>Raise incident</strong>: Automatically raise a new DataHub Incident for the Table whenever the Custom SQL Assertion is failing. This
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may indicate that the Table is unfit for consumption. Configure Slack Notifications under <strong>Settings</strong> to be notified when
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an incident is created due to an Assertion failure.</p></li><li><p><strong>Resolve incident</strong>: Automatically resolved any incidents that were raised due to failures in this Custom SQL Assertion. Note that
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any other incidents will not be impacted.</p></li></ul><p>Then click <strong>Next</strong>.</p><ol start="7"><li>(Optional) Add a <strong>description</strong> for the assertion. This is a human-readable description of the assertion. If you do not provide one, a description will be generated for you.</li></ol><p align="left"><img loading="lazy" width="40%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/shared/assertion-builder-description.png" class="img_ev3q"></p><ol start="8"><li>Click <strong>Save</strong>.</li></ol><p>And that's it! DataHub will now begin to monitor your Schema Assertion for the table.</p><p>Once your assertion has run, you will begin to see Success or Failure status:</p><p align="left"><img loading="lazy" width="45%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/schema/assertion-results.png" class="img_ev3q"></p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="stopping-a-schema-assertion">Stopping a Schema Assertion<a href="#stopping-a-schema-assertion" class="hash-link" aria-label="Direct link to Stopping a Schema Assertion" title="Direct link to Stopping a Schema Assertion"></a></h2><p>In order to temporarily stop the evaluation of the assertion:</p><ol><li>Navigate to the <strong>Quality</strong> tab of the Table with the assertion</li><li>Click <strong>Schema</strong> to open the Schema Assertion</li><li>Click the "Stop" button.</li></ol><p align="left"><img loading="lazy" width="25%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/shared/stop-assertion.png" class="img_ev3q"></p><p>To resume the assertion, simply click <strong>Start</strong>.</p><p align="left"><img loading="lazy" width="25%" src="https://raw.githubusercontent.com/datahub-project/static-assets/main/imgs/observe/shared/start-assertion.png" class="img_ev3q"></p><h2 class="anchor anchorWithStickyNavbar_LWe7" id="creating-schema-assertions-via-api">Creating Schema Assertions via API<a href="#creating-schema-assertions-via-api" class="hash-link" aria-label="Direct link to Creating Schema Assertions via API" title="Direct link to Creating Schema Assertions via API"></a></h2><p>Note that to create or delete Assertions and Monitors for a specific entity on DataHub, you'll need the
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<code>Edit Assertions</code> and <code>Edit Monitors</code> privileges to create schema assertion via API.</p><h4 class="anchor anchorWithStickyNavbar_LWe7" id="graphql">GraphQL<a href="#graphql" class="hash-link" aria-label="Direct link to GraphQL" title="Direct link to GraphQL"></a></h4><p>In order to create a Schema Assertions, you can use the <code>upsertDatasetSchemaAssertionMonitor</code> mutation.</p><h5 class="anchor anchorWithStickyNavbar_LWe7" id="examples">Examples<a href="#examples" class="hash-link" aria-label="Direct link to Examples" title="Direct link to Examples"></a></h5><p>To create a Schema Assertion that checks for a the presence of a specific set of columns:</p><div class="language-graphql codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#bfc7d5;--prism-background-color:#292d3e"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-graphql codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#bfc7d5"><span class="token keyword" style="font-style:italic">mutation</span><span class="token plain"> </span><span class="token definition-mutation function" style="color:rgb(130, 170, 255)">upsertDatasetSchemaAssertionMonitor</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token property-query">upsertDatasetSchemaAssertionMonitor</span><span class="token punctuation" style="color:rgb(199, 146, 234)">(</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token attr-name" style="color:rgb(255, 203, 107)">input</span><span class="token punctuation" style="color:rgb(199, 146, 234)">:</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(199, 146, 234)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#bfc7d5"><span class="token plain"> </span><span class="token attr-name" style="color:rgb(255, 203, 107)">entityUrn</span><span class="token punctuation" style="color:rgb(199, 146, 234)">:</span><span class="token plain"> </span><span class="token description string" style="color:rgb(195, 232, 141)">"</span><span class="token description string language-markdown tag punctuation" style="color:rgb(199, 146, 234)"><</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)">urn</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)"> </span><span class="token description string language-markdown tag attr-name" style="color:rgb(255, 203, 107)">of</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)"> </span><span class="token description string language-markdown tag attr-name" style="color:rgb(255, 203, 107)">the</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)"> </span><span class="token description string language-markdown tag attr-name" style="color:rgb(255, 203, 107)">table</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)"> </span><span class="token description string language-markdown tag attr-name" style="color:rgb(255, 203, 107)">to</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)"> </span><span class="token description string language-markdown tag attr-name" style="color:rgb(255, 203, 107)">be</span><span class="token description string language-markdown tag" style="color:rgb(255, 85, 114)"> </span><span class="token description string language-markdown tag attr-name" style="color:rgb(255, 203, 107)">monitored</span><span class="token description string language-markdown tag punctuation" style="color:rgb(199, 146, 234)">></span><span class="token description string
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