However, on MacOS it appears that Outlook uses a local SQLite DB to index the cached items but stores all of them (emails, calender items, etc.) as files deep inside your Outlook Profile directory.

In the Windows world, Outlook historically saved all this cached info in a single OST file.

I'm not an Outlook expert, but know it creates a local cache of all your Outlook items so you can view them when you're offline. I presume that when you first open Outlook or resume from a sleep state, it triggers a Calendar sync and then chokes on all those Calendar Items and Reminders across your personal calendar AND ALL the Shared Calendars. The problem is that when you add that many calendars, Outlook both downloads all those calendar items to a local cache (more on that below) but also keeps ALL those calendars sync'd. They're handy because you can quickly toggle someone's calendar on to check availability, schedule meetings, etc. No, those are not typos, so WTH is happening?!? Here's what I speculate.įor convenience, I had added about 25 Shared Calendars to my Calendar view but never displayed more than 2 or 3 at once. Mac OS Version: Version 11.5.1 (Build 20G80) Here are my specs from an Outlook for Mac Diagnostic Log: Performance impact mostly seen when doing anything related to Calendar functions When clicking to respond to a meeting reminder pop-up, spinning pinwheels of death for prolonged periods (sometimes several minutes). When viewed in Activity Monitor during these states, frequent 'Outlook not responding' messages Slow to open and VERY slow to respond either when being launched from an active session or when resuming from a sleep state.Įxcessive and prolonged CPU utilization during either state mentioned above I've been fighting performance issues with Outlook for weeks/months and finally figured out the culprit (for me, at least): Shared Calendars. Well, I've got a 2019 16' MacBook Pro with 32GB RAM and an Intel 8-core i9 CPU. Removing the Shared Calendars solved my performance issues. Tl dr: Having many Shared Calendars caused excessive CPU utilization & poor performance due to lengthy Outlook syncs.

Outlook para Mac lento