Mysql Join performance MongoDB, Cassandra - mysql

Question

I have a join query which takes a lot of time to process.
SELECT
COUNT(c.id)
FROM `customers` AS `c`
LEFT JOIN `setting` AS `ssh` ON `c`.`shop_id` = `ssh`.`id`
LEFT JOIN `customer_extra` AS `cx` ON `c`.`id` = `cx`.`customer_id`
LEFT JOIN `customers_address` AS `ca` ON `ca`.`id` = `cx`.`customer_default_address_id`
LEFT JOIN `lytcustomer_tier` AS `ct` ON `cx`.`lyt_customer_tier_id` = `ct`.`id`
WHERE (c.shop_id = '12121') AND ((DATE(cx.last_email_open_date) > '2019-11-08'));
This is primarily because the table 'customers' has 2 million records.
I could go over into indexing etc. But, the larger point is, this 2.5 million could become a billion records 1 day.
I'm looking for solutions which can enhance performance.
I've given thought to
a) horizontal scalability. -: distribute the mysql table into different sections and query the count independently.
b) using composite indexes.
c) My favourite one -: Just create a seperate collection in mongodb or redis which only houses the count(output of this query) Since, the count is just 1 number. this will not require a huge size aka better query performance (Only question is, how many such queries are there, because that will increase size of the new collection)

Answer 1

Try this and see if it improve performance:
SELECT
COUNT(c.id)
FROM `customers` AS `c`
INNER JOIN `customer_extra` AS `cx` ON `c`.`id` = `cx`.`customer_id`
LEFT JOIN `setting` AS `ssh` ON `c`.`shop_id` = `ssh`.`id`
LEFT JOIN `customers_address` AS `ca` ON `ca`.`id` = `cx`.`customer_default_address_id`
LEFT JOIN `lytcustomer_tier` AS `ct` ON `cx`.`lyt_customer_tier_id` = `ct`.`id`
WHERE (c.shop_id = '12121') AND ((DATE(cx.last_email_open_date) > '2019-11-08'));
As I mention in the comment, since the condition AND ((DATE(cx.last_email_open_date) > '2019-11-08'));, already made customers table to INNER JOIN with customer_extra table, you might just change it to INNER JOIN customer_extra AS cx ON c.id = cx.customer_id and follow it with other LEFT JOIN.
The INNER JOIN will at least get the initial result to only return any customer who have last_email_open_date value based on what has been specified.

Answer 2

Say COUNT(*), not COUNT(c.id)
Remove these; they slow down the query without adding anything that I can see:
LEFT JOIN `setting` AS `ssh` ON `c`.`shop_id` = `ssh`.`id`
LEFT JOIN `customers_address` AS `ca` ON `ca`.`id` = `cx`.`customer_default_address_id`
LEFT JOIN `lytcustomer_tier` AS `ct` ON `cx`.`lyt_customer_tier_id` = `ct`.`id`
DATE(...) makes that test not "sargable". This works for DATE or DATETIME; and this is much faster:
cx.last_email_open_date > '2019-11-08'
Consider whether that should be >= instead of >.
Need an index on shop_id. (Please provide SHOW CREATE TABLE.)
Don't use LEFT JOIN when JOIN would work equally well.
If customer_extra is columns that should have been in customer, now is the time to move them in. That would let you use this composite index for even more performance:
INDEX(shop_id, last_email_open_date) -- in this order
With those changes, a billion rows in MySQL will probably not be a problem. If it is, there are still more fixes I can suggest.