more on databases

mustafah15 · Jul 16, 2023 · c459a35 · c459a35
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diff --git a/pages/ACID.md b/pages/ACID.md
@@ -14,4 +14,6 @@ title: ACID
 		- If the multiple transactions are running concurrently, they should not be affected by each other; the result should be the same as the result obtained if the transactions were running sequentially.
 		- [[database isolation]]
 	- **Durability**
-		- Changes that have been committed to the database should remain even in the case of the software and hardware failure. for instance if x account contains 10$ this information should not disappear upon hardware or software failure.
+		- Changes that have been committed to the database should remain even in the case of software and hardware failure. for instance, if x account contains 10$ this information should not disappear upon hardware or software failure.
+		- [[database durability]]
+		-
diff --git a/pages/database durability techniques.md b/pages/database durability techniques.md
@@ -0,0 +1,6 @@
+- WAL - write-ahead log
+	- writing a lot of data to disk is expensive, which is why DBMSs persist a compressed version of the changes known as WAL
+- asynchronous snapshot
+	- In this approach everything we write is kept in-memory and later on, asynchronously, it’s snapshot is synced/ written to the drive (persisted disk/ SSD/ Hard-drive) all at once.
+- AOF - append-only file
+	- Very similar to the WAL strategy, It keeps track of only the changes happening. A very lightweight way of storing the changes and also gives the possibility of reconstructing the state of the system in case of failures.
diff --git a/pages/database durability.md b/pages/database durability.md
@@ -0,0 +1,6 @@
+- the process of ensuring persisting transaction permanently and do not accidentally disappear or get erased even during a database crash.
+- durability actions are slow because to make things durable that means you write to disk and writing to the disk is slow.
+- this means changes made by committed transactions must be persisted in a durable non-volatile storage.
+- [[database durability techniques]]
+- os cache
+	- most of DBMSs bypass the os cache to ensure durability by fsync os which can be expensive and slow down commits
diff --git a/pages/database isolation.md b/pages/database isolation.md
@@ -1,4 +1,3 @@
 - can my inflight transaction see changes made by other transactions?
 - [[database read phenomenas]]
-- [[database isolation levels]]
--
+- [[database isolation levels]]