# Exceptions

Follow a record from routing through processing and delivery. Whatever stops a record on the way is an exception, and you choose each exception's answer.

## Find the right answer

| What happened? | Exception | Where to answer it | Default |
| --- | --- | --- | --- |
| A pipeline lost a value | a parse, math, limits or encoding kind | Routes → Exceptions | tag, or ignore for encoding |
| No route or delivery condition took it | `Unmatched` | Routes → Exceptions | block |
| A batch could not be processed | `Unprocessable` | Routes → Exceptions | block |
| A destination refused a record | `Refused` | Routes → Exceptions | block |
| A destination could not be reached | none | [Repair its connection or service](/docs/delivery#hold) | Retry; pause input when buffers fill |

## Answer exceptions

Each exception has a kind, and each kind belongs to a category: parse, math, limits, encoding or delivery. The **Exceptions** on the Routes page give every kind in the group one of five answers:

-   **ignore:** the record goes on unmarked. Smeltr still counts the exception.
-   **tag:** the record goes on with its exceptions written to the [tag field](#tag).
-   **drop:** Smeltr counts the record and discards it.
-   **deliver:** the record goes to the destinations you pick, with its exceptions in the [tag field](#tag), each in its own [format](/docs/destinations#formats).
-   **block:** the source stops. Processing waits for a new deployment; Smeltr sends a refused record again until the destination takes it. Status → Issues shows it as Source blocked, or Blocked by destination refusals; [capture it](/docs/capture-sample#blocked) to see the records.

An answer for a category covers every kind in it, and a kind's own answer beats its category's. A record with several exceptions takes the strongest answer: block, then deliver, then drop, then tag, then ignore. The delivery kinds have no record on a route to tag, so you cannot ignore or tag them.

![The Exceptions on the Routes page: math is dropped, limits block the source, and Overflow, a math kind, is tagged.](/exception-answers-light.png)

The group's Exceptions on the Routes page. Overflow's answer beats its category's, so Overflow is tagged while the rest of math is dropped.

A route or a destination can answer differently from the group, under **Exceptions** in its card. A destination answers only the records it [refuses](/docs/delivery#refused).

## Tag and route

A tagged record carries its exceptions in `smeltr.exception`. Delivery conditions read that field to choose a destination. Use `smeltr.exception != null` to send tagged records to an investigation destination, and `smeltr.exception == null` to send only clean records to the normal one.

The **Tag field**, under **Exceptions** → **Advanced**, names another field for the group or for one route. If you rename it, update both conditions. See [unparsable records](/docs/steps/parser#unparsable) for examples you can test.

## When no route matches

A record that matches none of its source's routes is `Unmatched`. Blocking holds the records and pauses the source until a new deployment: add or correct a route, or change the answer, then review and deploy. Delivering keeps them in another destination for investigation or later processing.

Use [route conditions](/docs/routing/records) to decide what belongs in each pipeline. An unconditional route matches all records from its source, so no record of that source is left without a route.

Every record a pipeline finishes goes to a destination, is dropped by your pipeline, or is `Unmatched`: if no delivery condition takes it, it gets the `Unmatched` answer, delivered as the pipeline left it.

## When processing cannot finish

A batch Smeltr cannot process, including a record that exceeds its memory budget, is `Unprocessable`. Blocking waits for a new deployment. No pipeline finished the record, so a destination that writes the record writes `{"_raw": …}`.