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A comment on Show HN: Monty, Mongo tinified. MongoDB implemented in Python. Parent comment

Re:Show HN: Monty, Mongo tinified. MongoDB implemented in Py... by slver on Saturday May 29, 2021 @12:53PM (#27326517)
Its document model is vanilla BSON on disk.
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Re:Show HN: Monty, Mongo tinified. MongoDB implemented in Py... by avinassh on Saturday May 29, 2021 @01:45PM (#27326914)
It possible to update the BSON without loading the entire document in the memory? I am curious how Mongo does updates.
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Re:Show HN: Monty, Mongo tinified. MongoDB implemented in Py... by slver on Saturday May 29, 2021 @11:11PM (#27330290)
It’s a memory mapped file. If you update a bool or number value it’ll rewrite just that. If you update anything else it’ll often have to rewrite the entire document due to variable size.
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Re:Show HN: Monty, Mongo tinified. MongoDB implemented in Py... by MaBeuLux88 on Wednesday June 09, 2021 @06:56PM (#27454419)
That was true with MMAPv1. It's not since March 2015, when WiredTiger was introduced with MongoDB 3.0.
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Re:Show HN: Monty, Mongo tinified. MongoDB implemented in Py... by the-dude on Sunday May 30, 2021 @05:11AM (#27331787)
I assume when you say just that, it will write an entire page.
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Re:Show HN: Monty, Mongo tinified. MongoDB implemented in Py... by slver on Sunday May 30, 2021 @02:41PM (#27335450)
In practice yeah I guess.

But rewriting the document is more extensive, it might even have to be moved (because Mongo allocates certain number of bytes for it, and it might outgrow that).

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