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Database

HypoPG: Hypothetical indexes

HypoPG is PostgreSQL extension for creating hypothetical/virtual indexes. HypoPG allows users to rapidly create hypothetical/virtual indexes that have no resource cost (CPU, disk, memory) that are visible to the PostgreSQL query planner.

The motivation for HypoPG is to allow users to quickly search for an index to improve a slow query without consuming server resources or waiting for them to build.

Enable the extension

  1. Go to the Database page in the Dashboard.
  2. Click on Extensions in the sidebar.
  3. Search for "hypopg" and enable the extension.

Speeding up a query

Given the following table and a simple query to select from the table by id:


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create table account (
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id int,
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address text
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);
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insert into account(id, address)
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select
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id,
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id || ' main street'
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from
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generate_series(1, 10000) id;

We can generate an explain plan for a description of how the PostgreSQL query planner intends to execute the query.


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explain select * from account where id=1;
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QUERY PLAN
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-------------------------------------------------------
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Seq Scan on account (cost=0.00..180.00 rows=1 width=13)
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Filter: (id = 1)
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(2 rows)

Using HypoPG, we can create a hypothetical index on the account(id) column to check if it would be useful to the query planner and then re-run the explain plan.

Note that the virtual indexes created by HypoPG are only visible in the PostgreSQL connection that they were created in. Supabase connects to PostgreSQL through a connection pooler so the hypopg_create_index statement and the explain statement should be executed in a single query.


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select * from hypopg_create_index('create index on account(id)');
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explain select * from account where id=1;
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QUERY PLAN
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------------------------------------------------------------------------------------
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Index Scan using <13504>btree_account_id on hypo (cost=0.29..8.30 rows=1 width=13)
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Index Cond: (id = 1)
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(2 rows)

The query plan has changed from a Seq Scan to an Index Scan using the newly created virtual index, so we may choose to create a real version of the index to improve performance on the target query:


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create index on account(id);

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