Remove catalog index price update by schedule subscription

[unicoder88]

Hi there!

It saddens me to inform that I discovered a bug with update by schedule which results to a lot of reindex operations in Algolia.
In PR #666 , we subscribed to catalog_product_index_price in order to see changed catalog rule prices.
In Magento 2.3 this still works well when it comes to individual product updates, but it goes mad with full catalog_product_price reindex.

This is likely the reason behind reported issue https://github.com/algolia/algoliasearch-magento-2/issues/831 .

Steps to reproduce

1. In Magento 2.3.1, install latest Algolia and switch all indexes to update by schedule mode.
   Initially algolia_products_cl is empty.
2. Reindex prices, e.g. bin/magento indexer:reindex catalog_product_price
3. Check algolia_products_cl and find that all products IDs were added - meaning full Algolia reindex!
4. Truncate or delete records from algolia_products_cl, or note last record number.
5. Reindex prices 2-nd time, e.g. bin/magento indexer:reindex catalog_product_price
6. Check algolia_products_cl, and see that no new records were added.
7. Reindex prices 3-rd time, e.g. bin/magento indexer:reindex catalog_product_price
8. Check algolia_products_cl, and see that all product IDs were added again.

What happens:

Reason here is catalog_product_index_price_replica table.

In scheduled mode, triggers are originally created on catalog_product_index_price,
and catalog_product_index_price_replica is empty.

https://prnt.sc/pdzjdh
https://prnt.sc/pdzjl6

In this state (scenario A), full price reindex does following:

1. truncates catalog_product_index_price_replica.
2. fills it with fresh index data.
3. switches catalog_product_index_price_replica vs catalog_product_index_price.
   During this switch, triggers follow renamed tables - triggers are now assigned to catalog_product_index_price_replica table.

https://prnt.sc/pdzjvw

In scenario A, no triggers are fired, even if some prices actually changed.

With switched table and triggers now assigned to _replica table, next full reindex does following:

1. truncates catalog_product_index_price_replica. On delete triggers won't fire with TRUNCATE command.
2. fills it with fresh index data. --- problem here!
   On insert triggers add every product in catalog to algolia_products_cl table. https://prnt.sc/pdzkhz
3. switches catalog_product_index_price_replica vs catalog_product_index_price.
   Triggers follow renamed table and are now assigned to original catalog_product_index_price table - scneatio A.

And so with every full price reindex, scenario A - no updates at all - alternates with scneario B - all products are added to changelog.

Full price index update can happen quite often, and some modules even invalidate this index on every product save (Amasty_Shopby)!

I have not come up with a proper solution here yet, so we had to install an alternative module that makes a plugin to catalog rules reindexing and detects product price changes, and then inserts changed product IDs into algolia_products_cl table manually. But this is not generic enough.

Cleaning up

Removing subscription from mview.xml doesn't seem to delete evil triggers, so I had to come up with schema migration. Should any other unfortunate code subscribe to the same index, the triggers will get recreated on next setup:upgrade recurring run.

What do you guys think?

[bsuravech]

@unicoder88 Thanks for the correction and for submitting. I've left a comment on the dropTriggers portion of the PR. It's unlikely there is another subscription on this table but we don't want to explicitly drop a trigger if there are other mview subscriptions there.

[peterjaap]

@bsuravech @damcou @unicoder88 although I agree this PR in itself is good, it's not a fix in the sense that it fixes the underlying problem, right?

How are products which prices are updated because of catalog price rules now added to the queue for resyncing?

[peterjaap]

@bsuravech still unsure about this one - it seems to me there's still no valid solution for a price rule kicking in not updating the products in Algolia, right?