maokaihe/mini_lsm
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

update summary

Browse Source 
Signed-off-by: Alex Chi Z <iskyzh@gmail.com>
This commit is contained in:
Alex Chi Z
2024-01-30 14:52:08 +08:00
parent acc3c959aa
commit 417e81e302
3 changed files with 16 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
mini-lsm-book/src/week3-06-serializable.md
View File

@@ -102,11 +102,21 @@ You can skip the check if `write_set` is empty. A read-only transaction can alwa
You should also modify the `put`, `delete`, and `write_batch` interface in `LsmStorageInner`. We recommend you define a helper function `write_batch_inner` that processes a write batch. If `options.serializable = true`, `put`, `delete`, and the user-facing `write_batch` should create a transaction instead of directly creating a write batch. Your write batch helper function should also return a `u64` commit timestamp so that `Transaction::Commit` can correctly store the committed transaction data into the MVCC structure.
## Task 4: Garbage Collection
In this task, you will need to modify:
```
src/mvcc/txn.rs
```
When you commit a transaction, you can also clean up the committed txn map to remove all transactions below the watermark, as they will not be involved in any future serializable validations.
## Test Your Understanding
* If you have some experience with building a relational database, you may think about the following question: assume that we build a database based on Mini-LSM where we store each row in the relation table as a key-value pair (key: primary key, value: serialized row) and enable serializable verification, does the database system directly gain ANSI serializable isolation level capability? Why or why not?
* The thing we implement here is actually write snapshot-isolation (see [A critique of snapshot isolation](https://dl.acm.org/doi/abs/10.1145/2168836.2168853)) that guarantees serializable. Is there any cases where the execution is serializable, but will be rejected by the write snapshot-isolation validation?
* There are databases that claim they have serializable snapshot isolation support by only tracking the keys accessed in gets and scans. Do they really prevent write skews caused by phantoms? (Okay... Actually, I'm talking about [BadgerDB](https://dgraph.io/blog/post/badger-txn/).)
* There are databases that claim they have serializable snapshot isolation support by only tracking the keys accessed in gets and scans (instead of key range). Do they really prevent write skews caused by phantoms? (Okay... Actually, I'm talking about [BadgerDB](https://dgraph.io/blog/post/badger-txn/).)
We do not provide reference answers to the questions, and feel free to discuss about them in the Discord community.