How to handle caching counters by redis? - sql

Question

I am using Postgres as main DB and REDIS for caching. I am working on caching mechanism for one db query which takes to much time (It's about 5-6 JOINS + nested SELECTS). For now I am caching results of this query using SET 'some key' JSON.stringify(query.result). This works fine, however I have one column that cannot be cached - it is called commentsCount. It has to be always up to date. As a temporary solution, I am querying db just for this one particular field like this:
app.get('/post/getBySlug/:slug',function(req,res,next){
var cacheKey = req.params.slug+'|'+req.params.language; // "my-post-slug|en-us" for example
cache.get(cacheKey, function(err, post){
throw err if err;
if(post) {
db.getPostCommentsCount({ where: { id: post.id }}).done(function(err,commentsCount){
throw err if err;
post.commentsCount = commentsCount;
res.json(post);
next()
})
} else {
db.getFullPostBySlug(req.params.slug, req.params.language).done(function(err, post){
throw err if err;
cache.set(cacheKey, post);
res.json(post);
next();
})
}
})
})
But it is still now what I want, because main DB is still queried. Is there any standard/good practise on storing counters in REDIS? My comment insert function looks like this:
START TRANSACTION
INSERT INTO "Comments" VALUES (...) // insert comments
UPDATE "Posts" SET "commentsCount" = "commentsCount" + 1 WHERE "Posts"."id" = 123456 // update counter on post
COMMIT TRANSACTION
I am using transaction because I dont want comment to be inserted without incrementing comments count. As a "side" question - is it better to make 2 sql queries in transaction or write a trigger to handle incrementing counter??
According to my query (I posted link to gist in comments):
We dont plan more than 2 languages (though it is possible)
I made those counters because I have to keep counters separate per language, be able to order by those separate counters and also be able to order by sum of the counters (total for all languages) - I found it hard to make query that would order by sum of columns from separate rows while still returning those rows... (At the begining counters were stored in language translations).
Generally this query looks for post where exists translation with specific 'slug' and 'language' (slug+language on post translation is unique index). Morover post has to be published (isPublished = boolean) and post.status has to be 'published' (status = enum) or post.iscomingSoon has to be true (isComingSoon = boolean). Do you have idea what index/ordering I could add to this query? Or should I just remove limit?
In every translation table I keep language as TEXT. It can be for example en-us or zh-cn etc. Do you think I should make it enum or maybe I should make another table to store languages and just keep language_id in translations?
Author actually can be null :)