Is it possible to batch update table

[luoyuxia]

Currently, the clickhouse-jdbc doesn't support batch update table.
I wonder is it possible to modify clickhouse-jdbc to make it support the batch update.
if so, what's the best or elegant way to do that.
Should I send 'alter' statement one by one to clickhouse server in a batch?

[zhicwu]

Yes, batch processing is limited to insert at this point, because update and delete are too heavy and they're not recommended to use frequently. There's a light-weight version(see ClickHouse/ClickHouse#19627) under discussion, but it takes time to implement.

Anyway, I'm working on #296 which will resolve this - it's nothing special but executing statements one by one in synchronous mode.

[luoyuxia]

Thank you for your reply.

I have another question, does synchronous mode is neccessary? I mean when the mutations_sync = 0 (Mutations execute asynchronously), if first update a = 1 wher c = 2. and then second update a = 3 where c = 2. what's the eventually value of a? Can it guarantee eventually consistent?

[zhicwu]

I have another question, does synchronous mode is necessary?

It's not. Sorry I wasn't clear on this. It's controlled by mutations_sync, which defaults to 0(async) as in ClickHouse server. In a typical ELT scenario, you may want to enable synchronous mutation so that you can update something first and then query against the updated rows.

I mean when the mutations_sync = 0 (Mutations execute asynchronously), if first update a = 1 where c = 2. and then second update a = 3 where c = 2. what's the eventually value of a? Can it guarantee eventually consistent?

I'm not sure about implementation details like how it handles concurrent mutations(seems version-based), whether used a queue to serialize expensive operations or not, and of course its eventual consistency. I saw a similar question at ClickHouse/ClickHouse#23180 but no one answered. Perhaps you can ask the question on Telegram/Slack?

[luoyuxia]

Thank you very much!