felipecaputo / go-mysql-timezone-tests

A repo to test a possible improvement to go-mysql lib

Go MySQL driver Timestamp/Timezone validator

This repo was created with the idea to validate an improvement to go-mysql driver, since we found some problems working with TIMESTAMP fields in our project.

Problem

We have found that the time difference was happening when validating a time difference between the moment an action was taken from the user and now, and the data from the action was stored in the database.

When we were running locally, everything was working perfectly but, after deploy to staging there was an unexpected error. The system was telling that the difference was 3 hours more.

After we analyzed the problem we have found that:

• Driver uses, when not set, location from UTC
• Driver does not read the Timezone from the global or session from DB
• MySQL timestamp store data according to Timezone, based on session
• Combined loc argument and timezone argument from the connection string produced some different behaviors.

Behavior

ATTENTION: Database is en Europe/Sofia and images are considering America/Sao_Paulo
Considering: both loc and db variable
                Local time: 2020-05-11 18:29:54 -0300 -03,
                DB time: 2020-05-11 18:29:54 -0300 -03,
                Difference Local to DB: 0s

Considering: only loc
                Local time: 2020-05-11 18:29:54 -0300 -03,
                DB time: 2020-05-12 01:29:54 -0300 -03,
                Difference Local to DB: -7h0m0s

Considering: only DB variable
                Local time: 2020-05-11 21:29:54 +0000 UTC,
                DB time: 2020-05-11 18:29:54 +0000 UTC,
                Difference Local to DB: 3h0m0s

Considering: using none configuration
                Local time: 2020-05-11 21:29:54 +0000 UTC,
                DB time: 2020-05-12 01:29:54 +0000 UTC,
                Difference Local to DB: -4h0m0s

How to reproduce

I've built a simple app that exposes a post endpoint that allows you to post data to DB and read automatically.

There are 4 instances in the docker-compose.yml file and a MySQL database in this repo.

Source code from the program is in main.go

To run, you just need to run run.sh (and probably, need to give execution permissions to it before running chmod +x run.sh)

Proposal

Considering other database drivers, seems plausible that the driver could handle the timezone automatically, based on some configuration, considering it, and avoiding breaking anyone using the connection as it is now, I think that, creating a configTZ as a boolean configuration parameter, that default value will be false, to implement the timezone configuration behavior bellow, when set as true.

loc	nil	America/SaoPaulo	nil	America/Sao_Paulo
timezone	nil	nil	America/Sao_Paulo	Europa/Sofia
Behavior	Set loc to UTC and DB session to UTC OR Read from the database and set loc to the same timezone	After connect to database, configure session to America/Sao_Paulo timezone, and use it when parsing time	After connect to database, configure session to America/Sao_Paulo timezone, and use it when parsing time	Configure as specified by the user, but generates a warning, telling that TIMEZONE fields could face a difference after parse.