While that might technically work, Benedict, I am afraid that if we enable users to have this kind of power, they would start to set ALLOW FILTERING here and there in order to not think twice about their data model so they can just call it a day.
At the same time, we have a guardrail for allowing filtering. If we set a table to be allowed to be filtered on and we would have a guardrail to forbid it, which approach would be applied? ________________________________________ From: Benedict <bened...@apache.org> Sent: Friday, February 3, 2023 22:13 To: dev@cassandra.apache.org Subject: Re: Implicitly enabling ALLOW FILTERING on virtual tables NetApp Security WARNING: This is an external email. Do not click links or open attachments unless you recognize the sender and know the content is safe. Why not introduce a general table option that toggles ALLOW FILTERING behaviour and just flip it for virtual tables we want this behaviour for? Users can do it too, for their own tables for which it’s suitable. On 3 Feb 2023, at 20:59, Andrés de la Peña <adelap...@apache.org> wrote: For those eventual big virtual tables there is the mentioned flag indicating whether the table allows filtering without AF. I guess the question is how can a user know whether a certain virtual table is one of the big ones. That could be specified in the doc for each table, and it could also be included in the table properties, so it's displayed by DESCRIBE TABLE queries. On Fri, 3 Feb 2023 at 20:56, Chris Lohfink <clohfin...@gmail.com<mailto:clohfin...@gmail.com>> wrote: Just to 2nd what Scott days. While everything is in memory now, it may not be in the future, and if we add it implicitly, we are tying ourselves to be in memory only. However, I wouldn't -1 the idea. Another option may be a cqlsh option (ie like expand on/off) to always include a flag so it doesnt need to be added or something. Chris On Fri, Feb 3, 2023 at 1:24 PM C. Scott Andreas <sc...@paradoxica.net<mailto:sc...@paradoxica.net>> wrote: There are some ideas that development community members have kicked around that may falsify the assumption that "virtual tables are tiny and will fit in memory." One example is CASSANDRA-14629: Abstract Virtual Table for very large result sets https://issues.apache.org/jira/browse/CASSANDRA-14629 Chris's proposal here is to enable query results from virtual tables to be streamed to the client rather than being fully materialized. There are some neat possibilities suggested in this ticket, such as debug functionality to dump the contents of a raw SSTable via the CQL interface, or the contents of the database's internal caches. One could also imagine a feature like this providing functionality similar to a foreign data wrapper in other databases. I don't think the assumption that "virtual tables will always be small and always fit in memory" is a safe one. I don't think we should implicitly add "ALLOW FILTERING" to all queries against virtual tables because of this, in addition to concern with departing from standard CQL semantics for a type of tables deemed special. – Scott On Feb 3, 2023, at 6:52 AM, Maxim Muzafarov <mmu...@apache.org<mailto:mmu...@apache.org>> wrote: Hello Stefan, Regarding the decision to implicitly enable ALLOW FILTERING for virtual tables, which also makes sense to me, it may be necessary to consider changing the clustering columns in the virtual table metadata to regular columns as well. The reasons are the same as mentioned earlier: the virtual tables hold their data in memory, thus we do not benefit from the advantages of ordered data (e.g. the ClientsTable and its ClusteringColumn(PORT)). Changing the clustering column to a regular column may simplify the virtual table data model, but I'm afraid it may affect users who rely on the table metadata. On Fri, 3 Feb 2023 at 12:32, Andrés de la Peña <adelap...@apache.org<mailto:adelap...@apache.org>> wrote: I think removing the need for ALLOW FILTERING on virtual tables makes sense and would be quite useful for operators. That guard exists for performance issues that shouldn't occur on virtual tables. We also have a flag in case some future virtual table implementation has limitations regarding filtering, although it seems it's not the case with any of the existing virtual tables. It is not like we would promote bad habits because virtual tables are meant to be queried by operators / administrators only. It might even be quite the opposite, since in the current situation users might get used to routinely use ALLOW FILTERING for querying their virtual tables. It has been mentioned on the #cassandra-dev Slack thread where this started (1) that it's kind of an API inconsistency to allow querying by non-primary keys on virtual tables without ALLOW FILTERING, whereas it's required for regular tables. I think that a simply doc update saying that virtual tables, which are not regular tables, support filtering would be enough. Virtual tables are well identified by both the keyspace they belong to and doc, so users shouldn't have trouble knowing whether a table is virtual. It would be similar to the current exception for ALLOW FILTERING, where one needs to use it unless the table has an index for the queried column. (1) https://the-asf.slack.com/archives/CK23JSY2K/p1675352759267329 On Fri, 3 Feb 2023 at 09:09, Miklosovic, Stefan <stefan.mikloso...@netapp.com<mailto:stefan.mikloso...@netapp.com>> wrote: Hi list, the content of virtual tables is held in memory (and / or is fetched every time upon request). While doing queries against such table for a column outside of primary key, normally, users are required to specify ALLOW FILTERING. This makes total sense for "ordinary tables" for applications to have performant and effective queries but it kinds of loses the applicability for virtual tables when it literally holds just handful of entries in memory and it just does not matter, does it? What do you think about implicitly allowing filtering for virtual tables so we save ourselves from these pesky errors when we want to query arbitrary column and we need to satisfy CQL spec just to do that? It is not like we would promote bad habits because virtual tables are meant to be queried by operators / administrators only. We can also explicitly document this behavior. Among other options, we may try to implement secondary indices on virtual tables but I am not completely sure this is what we want because its complexity etc. Is it even necessary to put such complex logic in place just to be able to select any column on few entries in memory? I put together a draft here (1). It would be ever possible to implicitly allow filtering on virtual tables only and it would be implementator's responsibility to decide that, per table. For all virtual tables we currently have, I would enable this everywhere. I do not think there is any virtual table where we would not want to enable it or where people HAVE TO specify that. (1) https://github.com/apache/cassandra/pull/2131
