[SERVER-72289] Add a section about how Timestamping works to the catalog/README architecture guide Created: 20/Dec/22  Updated: 17/Jan/23

Status: Backlog
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Task Priority: Major - P3
Reporter: Dianna Hohensee (Inactive) Assignee: Backlog - Storage Execution Team
Resolution: Unresolved Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Assigned Teams:
Storage Execution
Participants:

 Description   

We do not appear to have a section dedicated to timestamps in the architecture guide. But we sure do get a lot of questions about it, both from members within our own team and from external team members.



 Comments   
Comment by Dianna Hohensee (Inactive) [ 03/Jan/23 ]

Things like

How we set the storage engine oldestTimestamp & stableTimestamp values, and the read window of durable history that they define.

Other means of pinning the oldestTimestamp, why we do it / what feature is supported thereby

How are timestamps allotted to new incoming writes – from handing out a timestamp, to commit.

What does timestamp 0 do, when used in writes and reads – immediate visibility to readers (I forget whether it can suddenly show up in already opened snapshots) and checkpoint behavior.

Bit tangential, but whether or not we write oplog entries for some writes, how that is controlled.

Sketch of protections we now have in place against untimestamped writes

There does appear to be a replication timestamps section to the repl README here, but I think there are more interesting details about timestamps from the storage/storage execution perspective. The repl README, actually, discusses all_durable, but it doesn't make mention of the fact that all_durable is in-memory and repl's lastDurable something or other timestamp represents the crash-durable timestamp.

Comment by Gregory Noma [ 03/Jan/23 ]

dianna.hohensee@mongodb.com there should be a section in the repl arch guide about timestamps, are there any additional things about timestamps that you're interested in?

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