Slow behavior in '--watch'

[DanielRosenwasser]

There have been a few cases reported by customers that using --watch has been on the slow side. We should elicit feedback to understand what's going on.

Examples:

• https://www.reddit.com/r/typescript/comments/48rzzq/protip_what_to_do_to_solve_the_current_slowness/
• https://gitter.im/Microsoft/TypeScript?at=56d86d9906ba9a282a28ecf1

[mhegazy]

//CC @zhengbli

[jeffreymorlan]

I've noticed this on Ubuntu (node v0.10.25). TypeScript 1.6 used to always detect changes within a second. 1.7 and 1.8 take about 2 seconds for a one-file project, and anywhere between 2-10 seconds for a large project.

It seems this only affects older versions of node. If I use node 4.0.0 or later, it's down to less than a second again.

[jhades]

this could be duplicate than #6178. I've noticed this in version 1.8.7

[zhengbli]

As @jeffreymorlan noticed, the current implementation does different things for new node (> v4.0) and older node. For the newer ones, it uses the non-polling watchers, which is fast. For the older node version, it uses polling watchers with a relatively large polling interval with concerns that a shorted polling interval might cause pains for HDD users on old machines.

@jhades, what is your environment when you notice this? What is your node version?

[vivainio]

I noticed this with one of the 1.8 prerelease versions (when I was experimenting with migration from 1.7 series, and "-m systemjs --outfile test.js"). 10 sec delay on windows. Just tried with current stable release, and can't reproduce it anymore. So possibly dupe of #6178

[jhades]

@zhengbli i'm on 4.2.1

[zhengbli]

@jhades Are you on Windows/Linux/Mac? Do you have a sample project that I can use to repro the issue? As I just tested on my windows machine with node 4.2.1 and TypeScript 1.8.7, changes in a project with 100+ ts files can be detected instantly with tsc --watch.

[jhades]

@zhengbli I'm on OSX 10.11.1

[DanielRosenwasser]

I have been seeing more and more projects suggesting/utilizing Watchman. Perhaps we should consider looking into it.

[chapati23]

tsc -w also got a LOT slower for me lately, tried all kinds of configs and debugging my code and external packages but it really seems this was introduced by typescript or node.

tried 1.7.3, 1.8.7 and 1.9.0-latest-dev on node 5.6 and node 5.7 (OSX 10.11.3), all take minimum 3-5sec to pick up file changes. unfortunately i can't really pinpoint which version exactly introduced the slow behavior but it definitely used to be a LOT faster.

[realyze]

Yep, 1.6 picks up the changes much faster (Mac OS X 10.11.2).

Update: With nvm and node 5.9.1 it's fast (< 1sec). My default node is 0.12 though.

[basarat]

I have been seeing more and more projects suggesting/utilizing Watchman. Perhaps we should consider looking into it.

Got excited, then saw poor windows support : https://facebook.github.io/watchman/docs/install.html Windows x64 on Windows Server 2012 R2 and later is currently in alpha status. 🌹