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| # Changelog of Vitess v21.0.0 | ||
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| # Release of Vitess v21.0.0 | ||
| ## Summary | ||
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| ### Table of Contents | ||
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| - **[Major Changes](#major-changes)** | ||
| - **[Deprecations and Deletions](#deprecations-and-deletions)** | ||
| - [Deprecated VTTablet Flags](#vttablet-flags) | ||
| - [Deletion of deprecated metrics](#metric-deletion) | ||
| - [Deprecated Metrics](#deprecations-metrics) | ||
| - **[Traffic Mirroring](#traffic-mirroring)** | ||
| - **[New VTGate Shutdown Behavior](#new-vtgate-shutdown-behavior)** | ||
| - **[Tablet Throttler: Multi-Metric support](#tablet-throttler)** | ||
| - **[Allow Cross Cell Promotion in PRS](#allow-cross-cell)** | ||
| - **[Support for recursive CTEs](#recursive-cte)** | ||
| - **[VTGate Tablet Balancer](#tablet-balancer)** | ||
| - **[Query Timeout Override](#query-timeout)** | ||
| - **[New Backup Engine](#new-backup-engine)** | ||
| - **[Dynamic VReplication Configuration](#dynamic-vreplication-configuration)** | ||
| - **[Reference Table Materialization](#reference-table-materialization)** | ||
| - **[New VEXPLAIN Modes: TRACE and KEYS](#new-vexplain-modes)** | ||
| - **[Errant GTID Detection on VTTablets](#errant-gtid-vttablet)** | ||
| - **[Automatically Replace MySQL auto_increment Clauses with Vitess Sequences](#auto-replace-mysql-autoinc-with-seq)** | ||
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| ## <a id="major-changes"/>Major Changes</a> | ||
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| ### <a id="deprecations-and-deletions"/>Deprecations and Deletions</a> | ||
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| #### <a id="vttablet-flags"/>Deprecated VTTablet Flags</a> | ||
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| - `queryserver-enable-settings-pool` flag, added in `v15`, has been on by default since `v17`. | ||
| It is now deprecated and will be removed in a future release. | ||
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| #### <a id="metric-deletion"/>Deletion of deprecated metrics</a> | ||
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| The following VTOrc metrics were deprecated in `v20`. They have now been deleted. | ||
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| | Metric Name | | ||
| |:--------------------------------------------:| | ||
| | `analysis.change.write` | | ||
| | `audit.write` | | ||
| | `discoveries.attempt` | | ||
| | `discoveries.fail` | | ||
| | `discoveries.instance_poll_seconds_exceeded` | | ||
| | `discoveries.queue_length` | | ||
| | `discoveries.recent_count` | | ||
| | `instance.read` | | ||
| | `instance.read_topology` | | ||
| | `emergency_reparent_counts` | | ||
| | `planned_reparent_counts` | | ||
| | `reparent_shard_operation_timings` | | ||
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| #### <a id="deprecations-metrics"/>Deprecated Metrics</a> | ||
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| The following metrics are now deprecated and will be deleted in a future release, please use their replacements. | ||
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| | Component | Metric Name | Replaced By | | ||
| |------------|:---------------------:|:-------------------------------:| | ||
| | `vttablet` | `QueryCacheLength` | `QueryEnginePlanCacheLength` | | ||
| | `vttablet` | `QueryCacheSize` | `QueryEnginePlanCacheSize` | | ||
| | `vttablet` | `QueryCacheCapacity` | `QueryEnginePlanCacheCapacity` | | ||
| | `vttablet` | `QueryCacheEvictions` | `QueryEnginePlanCacheEvictions` | | ||
| | `vttablet` | `QueryCacheHits` | `QueryEnginePlanCacheHits` | | ||
| | `vttablet` | `QueryCacheMisses` | `QueryEnginePlanCacheMisses` | | ||
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| ### <a id="traffic-mirroring"/>Traffic Mirroring</a> | ||
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| Traffic mirroring is intended to help reduce some of the uncertainty inherent to `MoveTables SwitchTraffic`. When | ||
| traffic mirroring is enabled, VTGate will mirror a percentage of traffic from one keyspace to another. | ||
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| Mirror rules may be enabled through `vtctldclient` with `MoveTables MirrorTraffic`. For example: | ||
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| ```bash | ||
| $ vtctldclient --server :15999 MoveTables --target-keyspace customer --workflow commerce2customer MirrorTraffic --percent 5.0 | ||
| ``` | ||
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| Mirror rules can be inspected with `GetMirrorRules`. | ||
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| ### <a id="new-vtgate-shutdown-behavior"/>New VTGate Shutdown Behavior</a> | ||
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| We added a new option to VTGate to disallow new connections while VTGate is shutting down, | ||
| while allowing existing connections to finish their work until they manually disconnect or until | ||
| the `--onterm_timeout` is reached, without getting a `Server shutdown in progress` error. | ||
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| This new behavior can be enabled by specifying the new `--mysql-server-drain-onterm` flag to VTGate. | ||
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| You can find more information about this option in the [RFC](https://github.com/vitessio/vitess/issues/15971). | ||
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| ### <a id="tablet-throttler"/>Tablet Throttler: Multi-Metric support</a> | ||
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| Up until `v20`, the tablet throttler would only monitor and use a single metric. That would be replication lag, by | ||
| default, or could be the result of a custom query. In this release, we introduce a major redesign so that the throttler | ||
| monitors and uses multiple metrics at the same time, including the above two. | ||
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| The default behavior now is to monitor all metrics, but only use `lag` (if the custom query is undefined) or the `custom` | ||
| metric (if the custom query is defined). This is backwards-compatible with `v20`. A `v20` `PRIMARY` is compatible with | ||
| a `v21` `REPLICA`, and a `v21` `PRIMARY` is compatible with a `v20` `REPLICA`. | ||
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| However, it is now possible to assign any combination of one or more metrics for a given app. The throttler | ||
| would then accept or reject the app's requests based on the health of _all_ assigned metrics. We have provided a pre-defined | ||
| list of metrics: | ||
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| - `lag`: replication lag based on heartbeat injection. | ||
| - `threads_running`: concurrent active threads on the MySQL server. | ||
| - `loadavg`: per core load average measured on the tablet instance/pod. | ||
| - `custom`: the result of a custom query executed on the MySQL server. | ||
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| Each metric has a default threshold which can be overridden by the `UpdateThrottlerConfig` command. | ||
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| The throttler also supports the catch-all `"all"` app name, and it is thus possible to assign metrics to **all** apps. | ||
| Explicit app to metric assignments will override the catch-all configuration. | ||
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| Metrics are assigned a default _scope_, which could be `self` (isolated to the tablet) or `shard` (max, aka **worst** | ||
| value among shard tablets). It is further possible to require a different scope for each metric. | ||
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| ### <a id="allow-cross-cell"/>Allow Cross Cell Promotion in PRS</a> | ||
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| Up until now if the users wanted to promote a replica in a different cell from the current primary | ||
| using `PlannedReparentShard`, they had to specify the new primary with the `--new-primary` flag. | ||
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| We have now added a new flag `--allow-cross-cell-promotion` that lets `PlannedReparentShard` choose a primary in a | ||
| different cell even if no new primary is provided explicitly. | ||
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| ### <a id="recursive-cte"/>Experimental support for recursive CTEs</a> | ||
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| We have added experimental support for recursive CTEs in Vitess. We are marking it as experimental because it is not yet | ||
| fully tested and may have some limitations. We are looking for feedback from the community to improve this feature. | ||
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| ### <a id="tablet-balancer"/>VTGate Tablet Balancer</a> | ||
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| When a VTGate routes a query and has multiple available tablets for a given shard / tablet type (e.g. REPLICA), the | ||
| current default behavior routes the query with local cell affinity and round robin policy. The VTGate Tablet Balancer | ||
| provides an alternate mechanism that routes queries to maintain an even distribution of query load to each tablet, while | ||
| preferentially routing to tablets in the same cell as the VTGate. | ||
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| The tablet balancer is enabled by a new flag `--enable-balancer` and configured by `--balancer-vtgate-cells` | ||
| and `--balancer-keyspaces`. | ||
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| See the [RFC ](https://github.com/vitessio/vitess/issues/12241) for more details on the design and configuration of this feature. | ||
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| ### <a id="query-timeout"/>Query Timeout Override</a> | ||
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| VTGate sends an authoritative query timeout to VTTablet when the `QUERY_TIMEOUT_MS` comment directive, | ||
| `query_timeout` session system variable, or `query-timeout` flag is set. | ||
| The order of precedence is: comment directive > session variable > VTGate flag. | ||
| VTTablet overrides its default query timeout with the value received from VTGate. | ||
| All timeouts are specified in milliseconds. | ||
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| When a query is executed inside a transaction, there is an additional nuance. The actual timeout used will be the smaller | ||
| of the transaction timeout and the query timeout. | ||
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| A query can also be set to have no timeout by using the `QUERY_TIMEOUT_MS` comment directive with a value of `0`. | ||
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| Example usage: | ||
| `select /*vt+ QUERY_TIMEOUT_MS=30 */ col from tbl` | ||
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| ### <a id="new-backup-engine"/>New Backup Engine (EXPERIMENTAL)</a> | ||
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| We are introducing a new backup engine for logical backups in order to support use cases that require something other | ||
| than physical backups. This feature is experimental and is based on [MySQL Shell](https://dev.mysql.com/doc/mysql-shell/8.0/en/). | ||
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| The new engine is enabled by using `--backup_engine_implementation=mysqlshell`. There are other options that are required, | ||
| so please read the [documentation](https://vitess.io/docs/21.0/user-guides/operating-vitess/backup-and-restore/creating-a-backup/) to learn which options are required and how to configure them. | ||
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| ### <a id="dynamic-vreplication-configuration"/>Dynamic VReplication Configuration</a> | ||
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| Previously, many of the configuration options for VReplication Workflows had to be provided using VTTablet flags. This | ||
| meant that any change to VReplication configuration required restarting VTTablets. We now allow these to be overridden | ||
| while creating a workflow or dynamically after the workflow is already in progress. | ||
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| ### <a id="reference-table-materialization"/>Reference Table Materialization</a> | ||
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| There is a new option in [`Materialize` workflows](https://vitess.io/docs/reference/vreplication/materialize/) to keep a synced copy of [reference or lookup tables](https://vitess.io/docs/reference/vreplication/reference_tables/) | ||
| (countries, states, zip codes, etc) from an unsharded keyspace, which holds the source of truth for the reference | ||
| table, to all shards in a sharded keyspace. | ||
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| ### <a id="new-vexplain-modes"/>New VEXPLAIN Modes: TRACE and KEYS</a> | ||
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| #### VEXPLAIN TRACE | ||
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| The new `TRACE` mode for `VEXPLAIN` provides a detailed execution trace of queries, showing how they're processed through various | ||
| operators and interactions with tablets. This mode is particularly useful for: | ||
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| - Identifying performance bottlenecks | ||
| - Understanding query execution patterns | ||
| - Optimizing complex queries | ||
| - Debugging unexpected query behavior | ||
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| `TRACE` mode runs the query and logs all interactions, returning a JSON representation of the query execution plan with additional | ||
| statistics like number of calls, average rows processed, and number of shards queried. | ||
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| #### VEXPLAIN KEYS | ||
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| The `KEYS` mode for `VEXPLAIN` offers a concise summary of query structure, highlighting columns used in joins, filters, and | ||
| grouping operations. This information is crucial for: | ||
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| - Identifying potential sharding key candidates | ||
| - Optimizing query performance | ||
| - Analyzing query patterns to inform database design decisions | ||
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| `KEYS` mode analyzes the query structure without executing it, providing JSON output that includes grouping columns, join columns, | ||
| filter columns (potential candidates for indexes, primary keys, or sharding keys), and the statement type. | ||
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| These new `VEXPLAIN` modes enhance Vitess's query analysis capabilities, allowing for more informed decisions about sharding | ||
| strategies and query optimization. | ||
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| ### <a id="errant-gtid-vttablet"/>Errant GTID Detection on VTTablets</a> | ||
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| VTTablets now run an errant GTID detection logic before they join the replication stream. So, if a replica has an errant GTID, it will | ||
| not start replicating from the primary. This protects us from running into situations which are very difficult to recover from. | ||
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| For users running with the vitess-operator on Kubernetes, this change means that replica tablets with errant GTIDs will have broken | ||
| replication and will report as unready. Users will need to manually replace and clean up these errant replica tablets. | ||
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| ### <a id="auto-replace-mysql-autoinc-with-seq"/>Automatically Replace MySQL auto_increment Clauses with Vitess Sequences</a> | ||
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| In https://github.com/vitessio/vitess/pull/16860 we added support for replacing MySQL `auto_increment` clauses with [Vitess Sequences](https://vitess.io/docs/reference/features/vitess-sequences/), performing all of the setup and initialization | ||
| work automatically during the [`MoveTables`](https://vitess.io/docs/reference/vreplication/movetables/) workflow. As part of that work we have deprecated the | ||
| [`--remove-sharded-auto-increment` boolean flag](https://vitess.io/docs/20.0/reference/programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_create/) and you should begin using the new | ||
| [`--sharded-auto-increment-handling` flag](https://vitess.io/docs/21.0/reference/programs/vtctldclient/vtctldclient_movetables/vtctldclient_movetables_create/) instead. Please see the new | ||
| [`MoveTables` Auto Increment Handling](https://vitess.io/docs/21.0/reference/vreplication/movetables/#auto-increment-handling) documentation for additional details. | ||
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| ## v21.0 | ||
| * **[21.0.0](21.0.0)** | ||
| * [Changelog](21.0.0/changelog.md) | ||
| * [Release Notes](21.0.0/release_notes.md) |