The syncing had been almost a black box for me, until I read through Edward Unthank's amazing breakdown. There's one paragraph that's pertinent to your exact situation here. Long delay between Marketo and SFDC? "Timeliness of sync between Marketo and Salesforce "Sync lead to SFDC" and "Add lead to SFDC Campaign" is immediate, without a queue. When a lead runs through that flow step, the sync to SFDC happens. Marketo program/SFDC campaign sync happens through a queue every 7 (or so) minutes. That's the one that you see in the Admin section of Marketo, where "Last time Salesforce was synced" is. While this happens every 7 (or so) minutes, there's a set limit of campaign syncs happening with each call, and extra campaign syncs will be queued, waiting for a later program/campaign sync opportunity if there's room next time. SO, Marketo program/SFDC campaign syncs are more API-call efficient, but you run into queueing bottlenecks faster. I don't remember exact throughput numbers, but when I was doing a huge sync, the leads-synced-per-hour was around 8,000. Lead updates also happen every 7 (or so) minutes. That is, when you update a field value on a lead in Marketo, it's checked against SFDC every time to see if the value is different, then if it's different, Marketo updates the new value in SFDC (or vice versa). This faces the same lead-value-change queueing problem as Marketo programs/SFDC campaigns."
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