datafusion-opensearch

Query OpenSearch (or Elasticsearch) indices with SQL and the DataFrame API through Apache DataFusion.

An index becomes a DataFusion table. Your WHERE is translated into the OpenSearch query DSL, the projection into _source, the LIMIT into the page size, and the result streams back page by page through a scroll cursor — so a scan is complete at any index size and memory stays bounded. Anything DataFusion asks for that cannot be translated exactly is applied by DataFusion in memory, so results are always correct: pushdown only ever narrows the request, never widens it.

Install

cargo add datafusion-opensearch

Add --features udf for OpenSearch-native full-text and geo predicates as SQL functions.

Quick start

SQL only — register the factory once, then point CREATE EXTERNAL TABLE at <cluster>/<index>:

use datafusion::prelude::SessionContext;
use datafusion_opensearch::OpenSearchTableProviderFactory;

#[tokio::main]
async fn main() -> datafusion::error::Result<()> {
    let ctx = SessionContext::new();
    OpenSearchTableProviderFactory::new().register(&ctx);

    ctx.sql("CREATE EXTERNAL TABLE docs STORED AS OPENSEARCH LOCATION 'http://localhost:9200/my-index'")
        .await?
        .collect()
        .await?;

    // WHERE → query DSL, the two columns → _source, LIMIT → page size.
    ctx.sql("SELECT id, status FROM docs WHERE speed > 40 AND status = 'OK' LIMIT 100")
        .await?
        .show()
        .await?;
    Ok(())
}

The column list is optional: without one the Arrow schema is derived from the index _mapping.

Every Rust example in this README is compiled by CI, so they are safe to copy.

Guide

Three ways to register an index

From SQL, as above. LOCATION is <base url>/<index>; OPTIONS accepts page_size, max_rows, sort ('ts:desc,id:asc') and base_filter (a JSON array of query-DSL clauses). Credentials set on the factory apply to every table it creates:

use datafusion::prelude::SessionContext;
use datafusion_opensearch::OpenSearchTableProviderFactory;

#[tokio::main]
async fn main() -> datafusion::error::Result<()> {
    let ctx = SessionContext::new();
    OpenSearchTableProviderFactory::new()
        .with_basic_auth("admin", "admin")
        .register(&ctx);
    ctx.sql(
        "CREATE EXTERNAL TABLE events (id VARCHAR, ts TIMESTAMP, level VARCHAR) \
         STORED AS OPENSEARCH LOCATION 'https://os.example.com/events' \
         OPTIONS ('sort' 'ts:desc', 'max_rows' '100000')",
    )
    .await?
    .collect()
    .await?;
    Ok(())
}

A whole cluster — every non-system index becomes a table, listed by SHOW TABLES (enable DataFusion's information_schema for that) and built lazily from its _mapping the first time it is queried:

use std::sync::Arc;
use datafusion::prelude::{SessionConfig, SessionContext};
use datafusion_opensearch::{OpenSearchClient, OpenSearchSchemaProvider};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let ctx = SessionContext::new_with_config(SessionConfig::new().with_information_schema(true));
    let os = OpenSearchSchemaProvider::connect(OpenSearchClient::new("http://localhost:9200")).await?;
    ctx.catalog("datafusion").unwrap().register_schema("os", Arc::new(os))?;

    ctx.sql("SHOW TABLES").await?.show().await?;
    ctx.sql("SELECT count(*) FROM os.\"my-index\"").await?.show().await?;
    Ok(())
}

One index, from Rust — with the schema inferred, or declared so only the listed columns are read (and an index that does not exist yet reads as empty):

use std::sync::Arc;
use datafusion::arrow::datatypes::{DataType, Field, Schema};
use datafusion::prelude::SessionContext;
use datafusion_opensearch::{OpenSearchClient, OpenSearchTableFactory, OpenSearchTableProvider};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let ctx = SessionContext::new();

    // Inferred from _mapping.
    let factory = OpenSearchTableFactory::new(OpenSearchClient::new("http://localhost:9200"));
    ctx.register_table("docs", factory.table_provider("my-index").await?)?;

    // Declared.
    let schema = Arc::new(Schema::new(vec![
        Field::new("id", DataType::Utf8, true),
        Field::new("speed", DataType::Float64, true),
    ]));
    ctx.register_table("fast", Arc::new(OpenSearchTableProvider::new("http://localhost:9200", "my-index", schema)))?;

    let df = ctx.table("fast").await?.filter(datafusion::prelude::col("speed").gt(datafusion::prelude::lit(40.0)))?;
    df.show().await?;
    Ok(())
}

What is pushed down

The provider translates these into the query DSL and tells DataFusion the filter is fully handled:

• col = v, col != v → term / must_not term
• col > v, >=, <, <=, BETWEEN → range (a literal on the left, 40 < col, is normalised)
• col IN (…), NOT IN → terms
• col IS NULL, IS NOT NULL → exists
• col LIKE 'abc%' → prefix; any other LIKE / ILIKE → wildcard (case-insensitive when ILIKE)
• AND, OR, NOT → bool.filter / bool.should / bool.must_not, all-or-nothing per branch
• comparisons on timestamp columns → epoch milliseconds, which OpenSearch's default date format accepts
• the projection → _source; LIMIT → the page size and a stop after that many rows

Everything else — a function or cast on a column, col = col, = NULL — stays in DataFusion and is evaluated on the rows that come back. An OR with one untranslatable side is not pushed at all, because pushing half of it would widen the result.

EXPLAIN shows the operator (OpenSearchExec) and, in verbose mode, the exact _search body that was sent.

Native predicates (feature udf)

Some of the most useful OpenSearch queries have no SQL spelling. With the udf feature they are scalar functions the provider pushes down as native queries:

• os_match(field, 'query') — the analysed full-text match
• os_geo_distance(field, lon, lat, radius_metres) — geo_distance
• os_geo_bbox(field, top_left_lon, top_left_lat, bottom_right_lon, bottom_right_lat) — geo_bounding_box
• os_geo_polygon(field, '[[lon,lat],[lon,lat],…]') — geo_polygon

use datafusion::prelude::SessionContext;
use datafusion_opensearch::OpenSearchTableProviderFactory;

#[tokio::main]
async fn main() -> datafusion::error::Result<()> {
    let ctx = SessionContext::new();
    OpenSearchTableProviderFactory::new().register(&ctx);
    #[cfg(feature = "udf")]
    for f in datafusion_opensearch::udf::all_udfs() {
        ctx.register_udf(f.as_ref().clone());
    }
    ctx.sql("CREATE EXTERNAL TABLE docs STORED AS OPENSEARCH LOCATION 'http://localhost:9200/my-index'")
        .await?
        .collect()
        .await?;
    ctx.sql("SELECT id FROM docs WHERE os_match(title, 'engine fault') AND os_geo_distance(pos, 24.94, 60.17, 5000)")
        .await?
        .show()
        .await?;
    Ok(())
}

Pushdown recognises the functions by name, so in a distributed setup every node that plans or executes must register them.

Streaming, limits and pagination

• A scan streams the whole result through a scroll cursor, one RecordBatch per page. Set the page size with with_page_size (default 5 000; the index's max_result_window, 10 000 by default, is the ceiling).
• A LIMIT stops the scan after that many rows. with_max_rows caps LIMIT-less scans if you need a safety net.
• with_sort pushes an order into _search, which makes LIMIT n mean "the first n by that order".
• For caller-driven cursor pagination, with_search_after reads exactly one page; feed the last row's sort values back in for the next one.
• with_partitions(n) (or OPTIONS ('partitions' '4')) reads through n DataFusion partitions in parallel, each an OpenSearch sliced scroll — worthwhile for large scans over multi-shard indices. A query with a LIMIT always uses one partition so the limit is exact.
• EXPLAIN ANALYZE reports the operator's output rows and elapsed time per partition.

use std::sync::Arc;
use datafusion::prelude::SessionContext;
use datafusion_opensearch::{OpenSearchClient, OpenSearchTableFactory};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let factory = OpenSearchTableFactory::new(OpenSearchClient::new("http://localhost:9200"));
    let table = factory
        .provider("events")
        .await?
        .with_sort(vec![("ts".into(), false)])
        .with_page_size(1_000)
        .with_max_rows(Some(50_000));
    let ctx = SessionContext::new();
    ctx.register_table("events", Arc::new(table))?;
    ctx.sql("SELECT id, ts FROM events WHERE level = 'ERROR' LIMIT 20").await?.show().await?;
    Ok(())
}

Always-on constraints

with_base_filter ANDs query-DSL clauses into every scan, beneath whatever the query asks for. Use it for row-level security, tenancy or soft-delete predicates the caller must never be able to opt out of. The clauses are opaque OpenSearch DSL, so anything the engine can express works:

use std::sync::Arc;
use datafusion::prelude::SessionContext;
use datafusion_opensearch::{OpenSearchClient, OpenSearchTableFactory};
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let factory = OpenSearchTableFactory::new(OpenSearchClient::new("http://localhost:9200"));
    let tenant_only = factory
        .provider("orders")
        .await?
        .with_base_filter(vec![json!({ "term": { "tenant": "acme" } }), json!({ "term": { "deleted": false } })]);
    let ctx = SessionContext::new();
    ctx.register_table("orders", Arc::new(tenant_only))?;
    // Every query on `orders` is scoped to acme's live rows, whatever its WHERE says.
    ctx.sql("SELECT count(*) FROM orders").await?.show().await?;
    Ok(())
}

Authentication and the HTTP client

use datafusion_opensearch::OpenSearchClient;

let with_password = OpenSearchClient::new("https://os.example.com").with_basic_auth("admin", "admin");
let with_token = OpenSearchClient::new("https://os.example.com").with_bearer_token("eyJ…");

// Or bring your own reqwest client for timeouts, TLS roots and custom headers.
let http = reqwest::Client::builder().timeout(std::time::Duration::from_secs(30)).build().unwrap();
let tuned = OpenSearchClient::new("https://os.example.com").with_client(http);

The client is rustls-only: no OpenSSL to link.

How mapping types become Arrow types

• keyword, text, wildcard, constant_keyword, ip → Utf8
• long, integer, short, byte, unsigned_long → Int64 (a whole-valued float such as 106.0 is accepted)
• double, float, half_float, scaled_float → Float64
• boolean → Boolean
• date, date_nanos → Timestamp(Millisecond, UTC), read from ISO 8601 strings or epoch milliseconds
• object, nested, geo_point, geo_shape and anything else → Utf8 holding the value's JSON text, to parse downstream

Every column is nullable; a field that is absent, null or of the wrong shape becomes null. When you declare the schema yourself (in Rust or in CREATE EXTERNAL TABLE), any string flavour (Utf8, Utf8View, LargeUtf8 — SQL VARCHAR), any integer or float width (INT, BIGINT, SMALLINT, FLOAT, DOUBLE, …), BOOLEAN and TIMESTAMP are read; integers out of the declared range become null rather than wrapping.

Errors

Anything the cluster returns other than success surfaces as a DataFusionError::External wrapping this crate's Error, which carries the URL, the HTTP status and the response body so the cause is in the message. Two deliberate exceptions: searching an index that does not exist reads as empty (a table can be registered before its index is created), while asking for the _mapping of a missing index is an error (there is no schema to fall back to).

Compatibility

Built against DataFusion 54; the crate tracks the DataFusion major line, so a DataFusion major bump is a minor bump here. Tested end to end against OpenSearch 2.x; the query DSL, scroll API and _cat/indices used here are shared with Elasticsearch 7 and 8.

Develop

cargo fmt --check
cargo clippy --all-targets --all-features -- -D warnings
cargo test --all-features                                         # unit + doc tests, no server needed
cargo test --all-features --test testcontainers -- --ignored      # end to end against a real OpenSearch (Docker)
OS_URL=http://localhost:9200 OS_INDEX=my-index cargo run --example basic

CI runs all of the above, including the end-to-end test, on every change, plus a build on the declared minimum Rust version.

Versioning and license

Plain semver on the DataFusion major line; tags vX.Y.Z at the published commit; see CHANGELOG.md. Apache-2.0, see LICENSE.