Tune vector query performance in AlloyDB for PostgreSQL

This page describes how to tune your indexes to achieve faster query performance and better recall in AlloyDB for PostgreSQL.

Analyze your queries

Use the EXPLAIN ANALYZE command to analyze your query insights as shown in the following example SQL query.

 EXPLAIN ANALYZE SELECT result-column  FROM my-table  ORDER BY EMBEDDING_COLUMN <-> embedding('text-embedding-005', 'What is a database?')::vector  LIMIT 1;

The example response QUERY PLAN includes information such as the time taken, the number of rows scanned or returned, and the resources used.

Limit (cost=0.42..15.27 rows=1 width=32) (actual time=0.106..0.132 rows=1 loops=1) -> Index Scan using my-scann-index on my-table (cost=0.42..858027.93 rows=100000 width=32) (actual time=0.105..0.129 rows=1 loops=1) Order By: (embedding_column <-> embedding('text-embedding-005', 'What is a database?')::vector(768)) Limit value: 1 Planning Time: 0.354 ms Execution Time: 0.141 ms

View vector index metrics

You can use vector index metrics to review performance of your vector index, identify areas for improvement, and tune your index based on the metrics, if needed. The pg_stat_ann_indexes view helps you understand the state of index utilization while the pg_stat_ann_index_creation view provides information about rows created at the time of index creation.

To view index utilization metrics, run the following command:

SELECT * FROM pg_stat_ann_indexes;

You see output similar to the following:

-[ RECORD 1 ]----------+--------------------------------------------------------------------------- relid | 271236 indexrelid | 271242 schemaname | public relname | t1 indexrelname | t1_ix1 indextype | scann indexconfig | {num_leaves=100,quantizer=SQ8} indexsize | 832 kB indexscan | 0 insertcount | 250 deletecount | 0 updatecount | 0 partitioncount | 100 distribution | {"average": 3.54, "maximum": 37, "minimum": 0, "outliers": [37, 12, 11, 10, 10, 9, 9, 9, 9, 9]} distributionpercentile |{"10": { "num_vectors": 0, "num_partitions": 0 }, "25": { "num_vectors": 0, "num_partitions": 30 }, "50": { "num_vectors": 3, "num_partitions": 30 }, "75": { "num_vectors": 5, "num_partitions": 19 }, "90": { "num_vectors": 7, "num_partitions": 11 }, "95": { "num_vectors": 9, "num_partitions": 5 }, "99": { "num_vectors": 12, "num_partitions": 4 }, "100": { "num_vectors": 37, "num_partitions": 1 }}

To view number of rows created at the time of index creation, run the following command:

SELECT * FROM pg_stat_ann_index_creation;

You see output similar to the following:

-[ RECORD 1 ]----------+--------------------------------------------------------------------------- relid | 271236 indexrelid | 271242 schemaname | public relname | t1 indexrelname | t1_ix1 index_rows_at_creation_time | 262144

For more information about the complete list of metrics, see Vector index metrics.

What's next