[jira] [Commented] (CASSANDRA-12268) Make MV Index creation robust for wide referent rows

["Carl Yeksigian (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-12268?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15404719#comment-15404719 ] 

Carl Yeksigian commented on CASSANDRA-12268:
--------------------------------------------

I've pushed the progress I've made so far on this ticket to a [branch|https://github.com/carlyeks/cassandra/tree/ticket/12268]. For the mutations which require merging with the previous values, we return a single collection of Mutations; for updates only (there are no base values to compare with, such as during building), we return each update as a mutation which gets written and pushed.

I am working on verifying that this provides a solution to the problem; if it does, I'll move onto working on the batching of mutations.

> Make MV Index creation robust for wide referent rows
> ----------------------------------------------------
>
>                 Key: CASSANDRA-12268
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12268
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Shook
>            Assignee: Carl Yeksigian
>
> When creating an index for a materialized view for extant data, heap pressure is very dependent on the cardinality of of rows associated with each index value. With the way that per-index value rows are created within the index, this can cause unbounded heap pressure, which can cause OOM. This appears to be a side-effect of how each index row is applied atomically as with batches.
> The commit logs can accumulate enough during the process to prevent the node from being restarted. Given that this occurs during global index creation, this can happen on multiple nodes, making stable recovery of a node set difficult, as co-replicas become unavailable to assist in back-filling data from commitlogs.
> While it is understandable that you want to avoid having relatively wide rows  even in materialized views, this represents a particularly difficult scenario for triage.
> The basic recommendation for improving this is to sub-group the index creation into smaller chunks internally, providing a maximal bound against the heap pressure when it is needed.



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