Altermv tutorial #34854
Altermv tutorial #34854
Conversation
| things like querying materialized views from different clusters, indexed vs. | ||
| non-indexed, and so on." | ||
|
|
||
| {{< if-released "v26.10" >}} |
There was a problem hiding this comment.
| FROM highest_bid_per_auction | ||
| WHERE end_time < mz_now(); | ||
| ``` | ||
| {{% include-example file="examples/create_materialized_view" example="example-create-materialized-view" %}} |
There was a problem hiding this comment.
I replaced this with the example from quickstart (with the modification of creating a view -> creating a materialized view).
|
|
||
| ## Details | ||
|
|
||
| ### Replacing a materialized view |
There was a problem hiding this comment.
| - name: "syntax-apply-replacement" | ||
| code: | | ||
| ALTER MATERIALIZED VIEW <name> APPLY REPLACEMENT <replacement_name>; | ||
| ALTER MATERIALIZED VIEW <name> APPLY REPLACEMENT <replacement_view>; |
There was a problem hiding this comment.
changed to view ... in case people thought we were renaming.
| the target materialized view. See [`CREATE REPLACEMENT MATERIALIZED VIEW | ||
| <replacement_view>...FOR <name>...`](/sql/create-materialized-view). | ||
|
|
||
| - name: "example-apply-replacement" |
There was a problem hiding this comment.
| Materialize supports a two-step process for replacing materialized views | ||
| in-place, i.e., without recreating downstream objects: | ||
|
|
||
| 1. **Create a replacement**: Use `CREATE REPLACEMENT MATERIALIZED VIEW` to |
There was a problem hiding this comment.
since there's the guide being written, I condensed this.
https://preview.materialize.com/materialize/34854/sql/create-materialized-view/#use-case
| #### Restrictions | ||
| #### Query performance of replacement views | ||
|
|
||
| - The replacement must have the same schema as the target materialized view: |
There was a problem hiding this comment.
I incorporated this not quite as a restriction ... but more on how to run the command
| --- | ||
| You cannot run `ALTER MATERIALIZED VIEW ... APPLY REPLACEMENT` command within a | ||
| transaction block. Instead, the `ALTER MATERIALIZED VIEW ... APPLY REPLACEMENT` | ||
| command must be run outside of an explicit transaction. |
There was a problem hiding this comment.
Oh ... actually, given that we only allow:
- read-only transactions (for SELECT only txn or SUBSCRIBE-based txns)
- insert-only transactions
We might not actually need this .. because the list of things we don't allow in a transaction block is everything but the aforementioned bullet points.
| ``` | ||
|
|
||
| If the target view is behind, it is recommended to drop the replacement | ||
| view instead of having it run for an extended period, buffering |
There was a problem hiding this comment.
Q: Is this something people can gauge by how far behind the target is? or is it just people check again after some time and see that it is still behind?
Q: Can people reduce the likelihood of the target being behind by applying the replacement view soon after it hydrates?
| If the replacement view is ahead of the target view, both the command and | ||
| the replacement view wait for the target view to catch up. During this | ||
| wait, the replacement view buffers any changes it receives from its | ||
| inputs, which, depending on the amount to buffer, could cause the cluster |
There was a problem hiding this comment.
Q: If someone runs the command before checking and it hangs, should we tell people to break out of it?
1 participant
Wanted to get a pulse on the changes before tweaking the guide a bit.
For ease of review, added a patch to fake the release of v26.10 (2d89321) which will be reverted before merging [hence, converted to draft]