`session.touch` is called on every request when `resave: false`

Description

[PR incoming with unit tests and implementation of option - default to no change from current behavior]

session.touch is called on every request when resave: false is set.

On in-memory stores such as connect-redis this has little impact other than additional traffic.

However, on disk-backed and/or globally replicated stores the costs can be significant, such as connect-dynamodb

Example Scenario with Costs - DynamoDB Store

DynamoDB Provisioned Capacity Pricing

• RCU = Read Capacity Unit
• WCU = Write Capacity Unit
• 60,000 RPM site / 60 seconds / minute = 1000 RPS
• Write on Every Request
  • 1,000 RPS requires
    • 1,000 RCU x $0.00013 = $0.13 / hour = $1,138 / year
    • 1,000 WCU x $0.00065 = $0.65 / hour = $5,964 / year
    • Total = $7,102 / year
• Write on Update or when 75% of originalMaxAge Expired
  • Assuming 1% of requests update the session or reach 75% of originalMaxAge
  • 1,000 RPS requires
    • 1,000 RCU x $0.00013 = $0.13 / hour = $1,138 / year
    • 10 WCU x $0.00065 = $0.0065 / hour = $57 / year
    • Total = $1,195
    • Savings = 83% vs Write on Every Request

Best cases for cost reduction

• Relatively longer sessions (e.g. minutes, hours, days, months, but not seconds)
• Session values infrequently updated

[dougwilson]

Hi @ragesoft 👋 . In your example, the query you are showing is not part of the resave feature, but rather that your store module is updating the expires column on your data store every time the session is accessed. That may be what you want, maybe not. Ideally the store would need to add an option on it’s end to allow you to control that behavior. This module just sends a signal to the store module that the session was accessed; what the store decides is the more appropriate thing to do with that signal is left up to the store module. I hope that helps.

[dougwilson]

There is a PR here: https://github.com/chill117/express-mysql-session/pull/133