Vlad-week3-DB #21
Vlad-week3-DB #21
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yunchen4
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yunchen4
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Hi Vlad,
You are doing a good job. I left a suggestion for deadlock situation. However I didn't find your answers for mongodb exercises. I have left a comment with the correct assignment file.
Please let me know on Slack when you complete it. Thank you and have a nice weekend!
| const fromRes = await db.query( | ||
| "SELECT balance FROM account WHERE account_number = $1 FOR UPDATE", | ||
| [fromAcc] | ||
| ); | ||
| const toRes = await db.query( | ||
| "SELECT balance FROM account WHERE account_number = $1 FOR UPDATE", | ||
| [toAcc] | ||
| ); |
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Suggestion: I see you want to lock the rows. It is better to always lock the rows based on a specific and predicted order, for example account ID with smaller number will be locked first. In this case the deadlock risk during high concurrency situation can be reduced. Otherwise, if two transactions happen almost the same time (for example account A->B and account B->A) the deadlock might happen.
| async function run() { | ||
| // 1) Connect | ||
| const client = new MongoClient(uri); | ||
| await client.connect(); | ||
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Needs rework: I didn't see the answers for exercises in this file?
yunchen4
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yunchen4
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LGTM, left a comment about possible blind spot.
| const updBushes = await col.updateMany( | ||
| { elements: "BUSHES" }, | ||
| { $set: { "elements.$": "BUSH" } } | ||
| ); |
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This is not wrong, but be aware that this query only updates the first occurance of BUSHES.
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