In Google Chrome, is it possible to set tabs to hibernate when not in use (to reduce memory usage)? I've noticed that Chrome starts to lag significantly on my machine when I have more than 20 tabs open. It's already possible to do this in Firefox (since some extensions have been developed for this purpose), but I haven't found any equivalent for Chrome.
You can try out the TooManyTabs extension for Chrome. One of its listed features:
Suspend idle tabs and save memory, organize with custom columns.
As the OP discovered, The Great Suspender1 used to do this job very well.
Unfortunately, as you can see in a comment below, its new maintainer has added some suspicious code. So I cannot recommend this right now.
There are various alternatives on the Chrome Store. For example: "Tiny Suspender" (simple, but not actively maintained) and "Auto Tab Discard" (advanced).
I myself wrote an old userscript called Hibernate Idle Tabs, which can work in multiple browsers, but I think the browser-specific extensions are likely to be more efficient.
There's a new kid on the block: The Great Discarder. This Chrome plugin claims to free up memory as well as CPU; and it seems to work. With The Great Suspender, you can go to Customize And Control Button | More Tools | Task Manager, and see the CPU and memory each tab takes up. When a tab is hibernated, it virtually stops using CPU; but you can see that the memory is still in use. When it is discarded, it doesn't even show up in the Task Manager.
You can go to chrome://discards/ to see the total and the free memory (but the sum of memory in tasks in the Task Manager, i.e. Chrome's memory usage, appears to be a big secret now). You can set The Great Discarder to discard pages inactive after e.g. 20 sec. It takes longer than 20 secs. to actually discard your tabs, but if you have a lot open, using a lot of memory, you can readily refresh the discards page, and see the memory in use drop. You can then set The Great Discarder to discard pages after any of several convenient intervals (although not after n seconds). On a few pages I tested, it also remembered where I was scrolled to on the page, when I navigated back to the tabs.
Unlike The Great Suspender, when you click on a discarded tab, it comes up right away, vs. having to click on the page too to restore it; which I like. This ain't one of your grandpappy's suspenders.