# Presto 316 Documentation

## 12.128. Release 0.116

## Cast between JSON and VARCHAR

Casts of both directions between JSON and VARCHAR have been removed. If you have such casts in your scripts or views, they will fail with a message when you move to release 0.116. To get the semantics of the current casts, use:

- `JSON_PARSE(x)` instead of `CAST(x as JSON)`
- `JSON_FORMAT(x)` instead of `CAST(x as VARCHAR)`

In a future release, we intend to reintroduce casts between JSON and VARCHAR along with other casts involving JSON. The semantics of the new JSON and VARCHAR cast will be consistent with the other casts being introduced. But it will be different from the semantics in 0.115 and before. When that comes, cast between JSON and VARCHAR in old scripts and views will produce unexpected result.

## Cluster Memory Manager Improvements

The cluster memory manager now has a low memory killer. If the cluster runs low on memory, the killer will kill queries to improve throughput. It can be enabled with the `query.low-memory-killer.enabled` config flag, and the delay between when the cluster runs low on memory and when the killer will be invoked can be configured with the `query.low-memory-killer.delay` option.

## General Changes

- Add `multimap_agg()` function.
- Add `checksum()` function.
- Add `max()` and `min()` that takes a second argument and produces `n` largest or `n` smallest values.
- Add `query_max_run_time` session property and `query.max-run-time` config. Queries are failed after the specified duration.
- Removed `experimental.cluster-memory-manager-enabled` config. The cluster memory manager is now always enabled.
- Removed `task.max-memory` config.
- `optimizer.optimize-hash-generation` and `distributed-joins-enabled` are both enabled by default now.
- Add optimization for `IF` on a constant condition.