lancedb/docs/web/tables/consistency.mdx

---
title: Consistency
sidebarTitle: "Consistency"
description: Learn about consistency settings and versioning in LanceDB tables.
icon: "water"
availability:
  oss: available
  enterprise: available
  summary: >-
    Read freshness can be set per connection in the embedded library and on a
    deployment. On a deployment, the default freshness comes from its
    configuration, and the connection setting can only make reads fresher.
---
import {
    PyConsistencyStrong as ConsistencyStrong,
    TsConsistencyStrong as TsConsistencyStrong,
    RsConsistencyStrong as RsConsistencyStrong,
    PyConsistencyEventual as ConsistencyEventual,
    TsConsistencyEventual as TsConsistencyEventual,
    RsConsistencyEventual as RsConsistencyEventual,
    PyConsistencyCheckoutLatest as ConsistencyCheckoutLatest,
    TsConsistencyCheckoutLatest as TsConsistencyCheckoutLatest,
    RsConsistencyCheckoutLatest as RsConsistencyCheckoutLatest,
    RsUpdateMakeUsersReader as RsConsistencyMakeUsersReader,
} from '/snippets/tables.mdx';

You can set `read_consistency_interval` on the connection to control how often reads check for updates from other writers.

There are three possible settings for `read_consistency_interval`:

1. **Unset (default)**: no automatic cross-process refresh checks.
2. **Zero seconds**: check for updates on every read (strongest freshness).
3. **Non-zero interval**: check for updates after the interval elapses (eventual refresh).

The value you set depends on your application's consistency needs and performance requirements.
For example, a real-time dashboard might require strong consistency, while a batch analytics job might be
fine with eventual consistency. Stronger consistency is not free — the smaller the interval, the more
often each read pays the cost of refreshing against object storage, which raises per-read latency and cost.

This setting works for both local ([LanceTable](/management/database#uris)) and remote
tables. It only affects read operations —
write operations are always consistent.

<Callout color="blue">
**Consistency in Remote Tables**

For remote tables (`db://` connections), `read_consistency_interval` is also
respected by the client. The interval is sent to the server as a freshness bound on each read:

- **Unset (default)**: no freshness bound is sent; reads are as fresh as the deployment's own setting, described below.
- **Zero seconds**: every read asks the server for the latest committed version.
- **Non-zero interval**: reads accept data at least as fresh as `now - interval`.

In addition, `checkout_latest` and `restore` set a time floor on that table handle: later
reads ask for data at least as fresh as that moment, or as the configured interval allows,
whichever is later. Each opened table handle keeps its own floor.

Each remote table handle also tracks the highest dataset version a response from the server has
reported and sends it back with every subsequent request, so successive reads on the same handle
never observe an older version even when a load balancer routes them to query nodes with
differently-cached views. `checkout_latest` resets this watermark.

A write also records its new version on the handle, but deployments do not use that record to
choose what a read sees, so the client alone does not guarantee that the next read reflects your
own write. To be sure it does, set the interval to zero, or call `checkout_latest` after writing.

Stronger consistency is not free — the smaller the interval, the more often each read pays the cost
of refreshing against storage, which raises per-read latency and cost.

In <Badge color="red">Enterprise</Badge> deployments, the server-side default freshness is still
controlled by the cluster-level `weak_read_consistency_interval_seconds` parameter; the client setting
tightens that bound on a per-connection basis. When the parameter is unset, every read is strongly
consistent; deployments installed from the Helm chart default it to 600 seconds.

<Tip>
30-60 seconds is a reasonable starting point for
`weak_read_consistency_interval_seconds`: it cuts unnecessary object-store
checks while keeping data fresh enough for most applications. This setting
only affects reads -- writes always remain strongly consistent.
</Tip>
</Callout>

## Configure Consistency Parameters {#configure-consistency-parameters}

To set strong consistency, set the interval to 0:

<CodeGroup>
    <CodeBlock filename="Python" language="Python" icon="python">
    {ConsistencyStrong}
    </CodeBlock>

    <CodeBlock filename="TypeScript" language="TypeScript" icon="square-js">
    {TsConsistencyStrong}
    </CodeBlock>

    <CodeBlock filename="Rust" language="Rust" icon="rust">
    {RsConsistencyStrong}
    </CodeBlock>
</CodeGroup>

<Expandable title="In the Rust snippets, a `make_users_reader` helper is used to build Arrow input data.">
<CodeGroup>
    <CodeBlock filename="Rust" language="Rust" icon="rust">
    {RsConsistencyMakeUsersReader}
    </CodeBlock>
</CodeGroup>
</Expandable>

For eventual consistency, use a non-zero interval:

<CodeGroup>
    <CodeBlock filename="Python" language="Python" icon="python">
    {ConsistencyEventual}
    </CodeBlock>

    <CodeBlock filename="TypeScript" language="TypeScript" icon="square-js">
    {TsConsistencyEventual}
    </CodeBlock>

    <CodeBlock filename="Rust" language="Rust" icon="rust">
    {RsConsistencyEventual}
    </CodeBlock>
</CodeGroup>


In the embedded library, with the default unset interval, tables do not auto-refresh from other writers.
To manually check for updates, use `checkout_latest` / `checkoutLatest`:

<CodeGroup>
    <CodeBlock filename="Python" language="Python" icon="python">
    {ConsistencyCheckoutLatest}
    </CodeBlock>

    <CodeBlock filename="TypeScript" language="TypeScript" icon="square-js">
    {TsConsistencyCheckoutLatest}
    </CodeBlock>

    <CodeBlock filename="Rust" language="Rust" icon="rust">
    {RsConsistencyCheckoutLatest}
    </CodeBlock>
</CodeGroup>

For reproducible reads, you can also pin a table to a specific snapshot with `checkout(...)` or
a tag, restore a table to a prior version, then return to the live table with
`checkout_latest` / `checkoutLatest`. See
[Versioning](/management/table#versioning) for the full version and tag workflow.

## Handle bad vectors {#handle-bad-vectors}

<Note>
This section is currently specific to the Python SDK.
</Note>

In LanceDB Python, you can use the `on_bad_vectors` parameter to choose how
invalid vector values are handled. Invalid vectors are vectors that are not valid
because:

1. They are the wrong dimension
2. They contain NaN values
3. They are null but are on a non-nullable field

By default, LanceDB will raise an error if it encounters a bad vector. You can
also choose one of the following options:

* `drop`: Ignore rows with bad vectors
* `fill`: Replace bad values (NaNs) or missing values (too few dimensions) with
    the fill value specified in the `fill_value` parameter. An input like
    `[1.0, NaN, 3.0]` will be replaced with `[1.0, 0.0, 3.0]` if `fill_value=0.0`.
* `null`: Replace bad vectors with null (only works if the column is nullable).
    A bad vector `[1.0, NaN, 3.0]` will be replaced with `null` if the column is
    nullable. If the vector column is non-nullable, then bad vectors will cause an
    error