apache / apache/paimon

[Feature] Using bitmap index to accelerate the query

Abierto
#4,530 2 comentarios 0 reacciones 0 asignados Ver en GitHub
enhancement
Lenguaje dominante
Java
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Forks
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Merge medio
1 d 9 h
PR fusionados (30 d)
423

Descripción

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/paimon/issues) and found nothing similar.

### Motivation

Currently we have introduced bitmap indexes. There are some optimisations that we can do when the user queries only against the bitmap indexed columns.

Suppose we have a table `usershop_behavior` with a bitmap index on the `gender` column and a bsi index on the `gmv` column.
```sql
CREATE TABLE usershop_behavior (
uid BIGINT
gender STRING,
gmv BIGINT
) WITH (
'file-index.bitmap.columns' = 'gender',
'file-index.bsi.columns' = 'gmv'
);
```

The bitmap index and bsi index can be used not only for filtering, but also for some simple aggregation like:
```sql
SELECT
gender,
COUNT(*) AS total,
SUM(gmv) AS total_gmv,
AVG(gmv) AS avg_gmv
FROM usershop_behavior
GROUP BY gender

SELECT
gender,
COUNT(*) AS total,
SUM(gmv) AS total_gmv,
AVG(gmv) AS avg_gmv
FROM usershop_behavior
WHERE gender='M'
GROUP BY gender
```

BSI index can be useful in topk scenarios
```sql
SELECT *
FROM usershop_behavior
ORDER BY gmv DESC
LIMIT 10;

SELECT *
FROM usershop_behavior
WHERE gender='M'
ORDER BY gmv DESC
LIMIT 10;
```

### Solution

Apache Flink and Apache Spark are already provides some interfaces. e.g.

Apache Flink:
`org.apache.flink.table.connector.source.abilities.SupportsAggregatePushDown`

Apache Spark:
`org.apache.spark.sql.connector.read.SupportsPushDownTopN`
`org.apache.spark.sql.connector.read.SupportsPushDownAggregates`

When queries hit the bitmap index rules, we can rewrite TableScan to BitmapIndexScan.

### Anything else?

Currently our index is designed to be used only for Data Skipping and it is not as reliable as filtering using partitioned keys. (We can't tell the flink&spark engine that filtering with indexes is reliable.)

This is because creating the index is split into several steps.
1. stop the ingesting task
2. using alter table to add index options
3. call rewrite index procedure
4. restart the ingesting task

We need to find a way to make indexes reliable, like partition keys. (e.g. throw exception when index is empty?)
Otherwise it's hard for our index to do its job.

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Guía de contribución

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Línea de trabajo

Comienza revisando las interfaces mencionadas SupportsAggregatePushDown y SupportsPushDownTopN, y luego sigue el proceso de cómo un TableScan podría reescribirse como BitmapIndexScan. Define cómo los índices bitmap y BSI admitirían las agregaciones y consultas top-k indicadas, incluido cómo deberían manejarse de forma fiable los índices ausentes o incompletos.

Escrito por el modelo de indexación a partir del texto del issue.

Evaluación

Stack tecnológico
java, spark
Área
data-engineering, databases, performance
Tipo de issue
Nueva funcionalidad
Dificultad
5/5
Tiempo estimado
Más de una semana
Estado de actividad
Estancado
Claridad
Necesita aclaración
Aptitud para principiantes
25/100

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