# Release of Vitess v18.0.0-rc1
## Summary

### Table of Contents

- **[Major Changes](#major-changes)**
    - **[Breaking Changes](#breaking-changes)**
        - [Local examples now use etcd v3 storage and API](#local-examples-etcd-v3)
    - **[New command line flags and behavior](#new-flag)**
        - [VTOrc flag `--allow-emergency-reparent`](#new-flag-toggle-ers)
        - [VTOrc flag `--change-tablets-with-errant-gtid-to-drained`](#new-flag-errant-gtid-convert)
        - [ERS sub flag `--wait-for-all-tablets`](#new-ers-subflag)
        - [VTGate flag `--grpc-send-session-in-streaming`](#new-vtgate-streaming-sesion)
    - **[Experimental Foreign Key Support](#foreign-keys)**
    - **[VTAdmin](#vtadmin)**
        - [Updated to node v18.16.0](#update-node)
    - **[Deprecations and Deletions](#deprecations-and-deletions)**
        - [Deprecated Flags](#deprecated-flags)
        - [Deprecated Stats](#deprecated-stats)
        - [Deleted Flags](#deleted-flags)
        - [Deleted `V3` planner](#deleted-v3)
        - [Deleted `k8stopo`](#deleted-k8stopo)
        - [Deleted `vtgr`](#deleted-vtgr)
        - [Deleted `query_analyzer`](#deleted-query_analyzer)
    - **[New Stats](#new-stats)**
        - [VTGate Vindex unknown parameters](#vtgate-vindex-unknown-parameters)
        - [VTBackup stat `Phase`](#vtbackup-stat-phase)
        - [VTBackup stat `PhaseStatus`](#vtbackup-stat-phase-status)
        - [Backup and restore metrics for AWS S3](#backup-restore-metrics-aws-s3)
        - [VTCtld and VTOrc reparenting stats](#vtctld-and-vtorc-reparenting-stats)
    - **[VTTablet](#vttablet)**
        - [VTTablet: New ResetSequences RPC](#vttablet-new-rpc-reset-sequences)
    - **[Docker](#docker)**
        - [Debian: Bookworm added and made default](#debian-bookworm)
        - [Debian: Buster removed](#debian-buster)
    - **[Durability Policies](#durability-policies)**
        - [New Durability Policies](#new-durability-policies)

## <a id="major-changes"/>Major Changes

### <a id="breaking-changes"/>Breaking Changes

#### <a id="local-examples-etcd-v3"/>Local examples now use etcd v3 storage and API
In previous releases the [local examples](https://github.com/vitessio/vitess/tree/main/examples/local) were
explicitly using etcd v2 storage (`etcd --enable-v2=true`) and API (`ETCDCTL_API=2`) mode. We have now
removed this legacy etcd usage and instead use the new (default) etcd v3 storage and API. Please see
[PR #13791](https://github.com/vitessio/vitess/pull/13791) for additional info. If you are using the local
examples in any sort of long-term non-testing capacity, then you will need to explicitly use the v2 storage
and API mode or [migrate your existing data from v2 to v3](https://etcd.io/docs/v3.5/tutorials/how-to-migrate/).

### <a id="new-flag"/>New command line flags and behavior

#### <a id="new-flag-toggle-ers"/>VTOrc flag `--allow-emergency-reparent`

VTOrc has a new flag `--allow-emergency-reparent` that allows the users to toggle the ability of VTOrc to run emergency
reparent operations. Users that want VTOrc to fix the replication issues, but don't want it to run any reparents
should start using this flag. By default, VTOrc will be able to run `EmergencyReparentShard`. Users must specify the
flag to `false` to change the behaviour.

#### <a id="new-flag-errant-gtid-convert"/>VTOrc flag `--change-tablets-with-errant-gtid-to-drained`

VTOrc has a new flag `--change-tablets-with-errant-gtid-to-drained` that allows users to choose whether VTOrc should change the
tablet type of tablets with errant GTIDs to `DRAINED`. By default, it is disabled.

This feature allows users to configure VTOrc such that any tablet that encounters errant GTIDs is automatically taken out of the
serving graph. These tablets can then be inspected for what the errant GTIDs are, and once fixed, they can rejoin the cluster.

#### <a id="new-ers-subflag"/>ERS sub flag `--wait-for-all-tablets`

Running `EmergencyReparentShard` from the vtctldclient has a new sub-flag `--wait-for-all-tablets` that makes `EmergencyReparentShard` wait
for a response from all the tablets. Originally `EmergencyReparentShard` was meant only to be run when a primary tablet is unreachable.
We have realized now that there are cases when the replication is broken but all the tablets are reachable. In these cases, it is advisable to
call `EmergencyReparentShard` with `--wait-for-all-tablets` so that it does not ignore one of the tablets.

#### <a id="new-vtgate-streaming-sesion"/>VTGate GRPC stream execute session flag `--grpc-send-session-in-streaming`

This flag enables transaction support on `StreamExecute` api.
Once enabled, VTGate `StreamExecute` gRPC api will send session as the last packet in the response.
The client should enable it only when they have made the required changes to expect such a packet.

It is disabled by default.

### <a id="foreign-keys"/>Experimental Foreign Key Support

A new field `foreignKeyMode` has been added to the VSchema. This field can be provided for each keyspace. The VTGate flag `--foreign_key_mode` has been deprecated in favour of this field.

There are 3 foreign key modes now supported in Vitess -
1. `FK_UNMANAGED` -
   This mode represents the default behaviour in Vitess, where it does not manage foreign keys column references. Users are responsible for configuring foreign keys in MySQL in such a way that related rows, as determined by foreign keys, reside within the same shard.
2. `FK_MANAGED` [EXPERIMENTAL] -
   In this experimental mode, Vitess is fully aware of foreign key relationships and actively tracks foreign key constraints using the schema tracker. Vitess takes charge of handling DML operations with foreign keys cascading updates, deletes and verifying restrict. It will also validate parent row existence.
   This ensures that all the operations are logged in binary logs, unlike MySQL implementation of foreign keys.
   This enables seamless integration of VReplication with foreign keys.
   For more details on what operations Vitess takes please refer to the [design document for foreign keys](https://github.com/vitessio/vitess/issues/12967).
3. `FK_DISALLOW` -
   In this mode Vitess explicitly disallows any DDL statements that try to create a foreign key constraint. This mode is equivalent to running VTGate with the flag `--foreign_key_mode=disallow`.

#### Upgrade process

After upgrading from v17 to v18, the users should specify the correct foreign key mode for all their keyspaces in the VSchema using the new property.
Once this change has taken effect, the deprecated flag `--foreign_key_mode` can be dropped from all the VTGates.

### <a id="vtadmin"/>VTAdmin

#### <a id="updated-node"/>vtadmin-web updated to node v18.16.0 (LTS)

Building `vtadmin-web` now requires node >= v18.16.0 (LTS). Breaking changes from v16 to v18 are listed
in https://nodejs.org/en/blog/release/v18.0.0, but none apply to VTAdmin. Full details on v18.16.0 are listed
on https://nodejs.org/en/blog/release/v18.16.0.

### <a id="deprecations-and-deletions"/>Deprecations and Deletions

#### <a id="deprecated-flags"/>Deprecated Command Line Flags

Throttler related `vttablet` flags:

- `--throttle_threshold` is deprecated and will be removed in `v19.0`
- `--throttle_metrics_query` is deprecated and will be removed in `v19.0`
- `--throttle_metrics_threshold` is deprecated and will be removed in `v19.0`
- `--throttle_check_as_check_self` is deprecated and will be removed in `v19.0`
- `--throttler-config-via-topo` is deprecated after assumed `true` in `v17.0`. It will be removed in a future version.

Cache related `vttablet` flags:

- `--queryserver-config-query-cache-lfu` is deprecated and will be removed in `v19.0`. The query cache always uses a LFU implementation now.
- `--queryserver-config-query-cache-size` is deprecated and will be removed in `v19.0`. This option only applied to LRU caches, which are now unsupported.

Buffering related `vtgate` flags:

- `--buffer_implementation` is deprecated and will be removed in `v19.0`

Cache related `vtgate` flags:

- `--gate_query_cache_lfu` is deprecated and will be removed in `v19.0`. The query cache always uses a LFU implementation now.
- `--gate_query_cache_size` is deprecated and will be removed in `v19.0`. This option only applied to LRU caches, which are now unsupported.

VTGate flags:

- `--schema_change_signal_user` is deprecated and will be removed in `v19.0`
- `--foreign_key_mode` is deprecated and will be removed in `v19.0`. For more detail read the [foreign keys](#foreign-keys) section.

VDiff v1:

[VDiff v2 was added in Vitess 15.0](https://vitess.io/blog/2022-11-22-vdiff-v2/) and marked as GA in 16.0.
The [legacy v1 client command](https://vitess.io/docs/18.0/reference/vreplication/vdiffv1/) is now deprecated in Vitess 18.0 and will be **removed** in 19.0.
Please switch all of your usage to the [new VDiff client](https://vitess.io/docs/18.0/reference/vreplication/vdiff/) command ASAP.


#### <a id="deprecated-stats"/>Deprecated Stats

The following `EmergencyReparentShard` stats are deprecated in `v18.0` and will be removed in `v19.0`:
- `ers_counter`
- `ers_success_counter`
- `ers_failure_counter`

These metrics are replaced by [new reparenting stats introduced in `v18.0`](#vtctld-and-vtorc-reparenting-stats).

VTBackup stat `DurationByPhase` is deprecated. Use the binary-valued `Phase` stat instead.

#### <a id="deleted-flags"/>Deleted Command Line Flags

Flags in `vtcombo`:
- `--vtctld_addr`

Flags in `vtctldclient ApplySchema`:
- `--skip-preflight`

Flags in `vtctl ApplySchema`:
- `--skip_preflight`

Flags in `vtgate`:
- `--vtctld_addr`

Flags in `vttablet`:
- `--vtctld_addr`
- `--use_super_read_only`
- `--disable-replication-manager`
- `--init_populate_metadata`
- `--queryserver-config-pool-prefill-parallelism`
- `--queryserver-config-stream-pool-prefill-parallelism`
- `--queryserver-config-transaction-pool-prefill-parallelism`
- `--queryserver-config-schema-change-signal-interval`
- `--enable-lag-throttler`

Flags in `vtctld`:
- `--vtctld_show_topology_crud`
- `--durability_policy`

Flags in `vtorc`:
- `--lock-shard-timeout`
- `--orc_web_dir`

#### <a id="deleted-v3"/>Deleted `v3` planner

The `Gen4` planner has been the default planner since Vitess 14. The `v3` planner was deprecated in Vitess 15 and has now been removed in this release.

#### <a id="deleted-k8stopo"/>Deleted `k8stopo`

The `k8stopo` has been deprecated in Vitess 17, also see https://github.com/vitessio/vitess/issues/13298. With Vitess 18
the `k8stopo` has been removed.

#### <a id="deleted-vtgr"/>Deleted `vtgr`

The `vtgr` has been deprecated in Vitess 17, also see https://github.com/vitessio/vitess/issues/13300. With Vitess 18 `vtgr` has been removed.

#### <a id="deleted-query_analyzer"/>Deleted `query_analyzer`

The undocumented `query_analyzer` binary has been removed in Vitess 18, see https://github.com/vitessio/vitess/issues/14054.

### <a id="new-stats"/>New stats

#### <a id="vtgate-vindex-unknown-parameters"/>VTGate Vindex unknown parameters

The VTGate stat `VindexUnknownParameters` gauges unknown Vindex parameters found in the latest VSchema pulled from the topology.

#### <a id="vtbackup-stat-phase"/>VTBackup `Phase` stat

In v17, the `vtbackup` stat `DurationByPhase` stat was added measuring the time spent by `vtbackup` in each phase. This stat turned out to be awkward to use in production, and has been replaced in v18 by a binary-valued `Phase` stat.

`Phase` reports a 1 (active) or a 0 (inactive) for each of the following phases:

* `CatchupReplication`
* `InitialBackup`
* `RestoreLastBackup`
* `TakeNewBackup`

To calculate how long `vtbackup` has spent in a given phase, sum the 1-valued data points over time and multiply by the data collection or reporting interval. For example, in Prometheus:

```
sum_over_time(vtbackup_phase{phase="TakeNewBackup"}) * <interval>
```
#### <a id="vtbackup-stat-phase-status"/>VTBackup `PhaseStatus` stat

`PhaseStatus` reports a 1 (active) or a 0 (inactive) for each of the following phases and statuses:

* `CatchupReplication` phase has statuses `Stalled` and `Stopped`.
    * `Stalled` is set to `1` when replication stops advancing.
    * `Stopped` is set to `1` when replication stops before `vtbackup` catches up with the primary.

#### <a id="backup-restore-metrics-aws-s3"/>Backup and restore metrics for AWS S3

Requests to AWS S3 are instrumented in backup and restore metrics. For example:

```
vtbackup_backup_count{component="BackupStorage",implementation="S3",operation="AWS:Request:Send"} 823
vtbackup_backup_duration_nanoseconds{component="BackupStorage",implementation="S3",operation="AWS:Request:Send"} 1.33632421437e+11
vtbackup_restore_count{component="BackupStorage",implementation="S3",operation="AWS:Request:Send"} 165
vtbackup_restore_count{component="BackupStorage",implementation="S3",operation="AWS:Request:Send"} 165
```

#### <a id="vtctld-and-vtorc-reparenting-stats"/>VTCtld and VTOrc reparenting stats

New VTCtld and VTorc stats were added to measure frequency of reparents by keyspace/shard:
- `emergency_reparent_counts` - Number of times `EmergencyReparentShard` has been run. It is further subdivided by the keyspace, shard and the result of the operation.
- `planned_reparent_counts` - Number of times `PlannedReparentShard` has been run. It is further subdivided by the keyspace, shard and the result of the operation.

Also, the `reparent_shard_operation_timings` stat was added to provide per-operation timings of reparent operations.

### <a id="vttablet"/>VTTablet

#### <a id="vttablet-new-rpc-reset-sequences"/>New ResetSequences rpc

A new VTTablet RPC `ResetSequences` has been added, which is being used by `MoveTables` and `Migrate` for workflows
where a `sequence` table is being moved (https://github.com/vitessio/vitess/pull/13238). This has an impact on the
Vitess upgrade process from an earlier version if you need to use such a workflow before the entire cluster is upgraded.

Any MoveTables or Migrate workflow that moves a sequence table should only be run after all vitess components have been
upgraded, and no upgrade should be done while such a workflow is in progress.

#### <a id="vttablet-tx-throttler-dry-run"/>New Dry-run/monitoring-only mode for the transaction throttler

A new CLI flag `--tx-throttler-dry-run` to set the Transaction Throttler to monitoring-only/dry-run mode has been added.
If the transaction throttler is enabled with `--enable-tx-throttler` and the new dry-run flag is also specified, the
tablet will not actually throttle any transactions; however, it will increase the counters for transactions throttled
(`vttablet_transaction_throttler_throttled`). This allows users to deploy the transaction throttler in production and
gain observability on how much throttling would take place, without actually throttling any requests.

### <a id="docker"/>Docker

#### <a id="debian-bookworm"/>Bookworm added and made default

Bookworm was released on 2023-06-10, and will be the new default base container for Docker builds.
Bullseye images will still be built and available as long as the OS build is current, tagged with the `-bullseye` suffix.

#### <a id="debian-buster"/>Buster removed

Buster LTS supports will stop in June 2024, and Vitess v18.0 will be supported through October 2024.
To prevent supporting a deprecated buster build for several months after June 2024, we are preemptively
removing Vitess support.

### <a id="durability-policies"/>Durability Policies

#### <a id="new-durability-policies"/>New Durability Policies

2 new inbuilt durability policies have been added to Vitess in this release namely `semi_sync_with_rdonly_ack` and `cross_cell_with_rdonly_ack`. These policies are exactly like `semi_sync` and `cross_cell` respectively, and differ just in the part where the rdonly tablets can also send semi-sync ACKs.

------------
The entire changelog for this release can be found [here](https://github.com/vitessio/vitess/blob/main/changelog/18.0/18.0.0/changelog.md).

The release includes 361 merged Pull Requests.

Thanks to all our contributors: @GuptaManan100, @Juneezee, @adsr, @ajm188, @app/dependabot, @app/github-actions, @app/vitess-bot, @arvind-murty, @austenLacy, @brendar, @davidpiegza, @dbussink, @deepthi, @derekperkins, @ejortegau, @frouioui, @harshit-gangal, @hkdsun, @jfg956, @jspawar, @mattlord, @maxenglander, @mdlayher, @notfelineit, @olyazavr, @pbibra, @peterlyoo, @rafer, @rohit-nayak-ps, @shlomi-noach, @systay, @timvaillancourt, @vmg, @yields
