Experimental POC: Materialized Views

[rohit-nayak-ps]

Description

This PR is an experiment in materializing joined tables to determine if it can be reliably built, estimate the complexity of implementing it with the current VReplication framework, and identify inherent limitations.

Current Implementation

User View

• Utilize Materialize with a single table-setting where the query is a view. The view should include a directive like select /*vt+ view=orders_view */.
• The target and source keyspace must be the same.
• The filter generated by Materialize has the materialized view's table name as the match, and the filter is the view query.
• The view must contain the primary key columns for each participating table, each part of an index. This ensures that updates and deletes to lookup tables, which result in bulk DMLs, are more efficient.
• Initially, only integer primary keys are supported until we better understand the consequences of bulk DMLs and supporting views.

Todos

• Remove hardcoded column name for base table!
• Handle case where column names are repeated across joined tables
• More unit tests in vplayer for join plans
• More unit tests in vstreamer for join plans
• Validation for parameters and view query: all PKs to be specified, required directive,
• Remove excess logs
• Allow target keyspace to be different: in that case we need to also replicate the lookup tables since future inserts will otherwise fail, as we exec the view query to get the new row whenever there is an insert into the base row.!

Related Issue(s)

RFC todo

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

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[github-actions]

This PR is being marked as stale because it has been open for 30 days with no activity. To rectify, you may do any of the following:

• Push additional commits to the associated branch.
• Remove the stale label.
• Add a comment indicating why it is not stale.

If no action is taken within 7 days, this PR will be closed.

[github-actions]

This PR was closed because it has been stale for 7 days with no activity.

[rohit-nayak-ps]

One challenge we encountered while implementing this PR is the potential exponential increase in write QPS due to updates in the lookup tables. For instance, if a country name is modified, the change would require updating all rows referencing that country in the view table. In cases where millions of rows are affected, this would result in a large-scale table update, significantly increasing write latency and potentially causing application unavailability.

Additionally, such a large update would lead to a spike in replica lags, leaving the view table with stale data during the update period, as subsequent updates would be queued behind the large update.

Given these challenges, we’ve decided to temporarily put this implementation on hold until we identify a more efficient way to address the issue.