blog

commit: 7f3c6d37d21e703e364474c5d730584e3367442f
parent 39787baaef26153da283eb6bbd150a05bef69da8
Author: Haelwenn (lanodan) Monnier <contact@hacktivis.me>
Date:   Mon, 13 Mar 2023 22:21:46 +0100

notes/unix-defects: Filesystem lack of transactions

Diffstat:
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notes/index.xhtml
2
+-
M
notes/unix-defects.xhtml
11
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2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/notes/index.xhtml b/notes/index.xhtml
@@ -52,7 +52,7 @@
 				<tr><td><a href="systems.json">systems.json</a></td><td data-value="642" data-type="int">642 B</td><td>2023-01-09 20:04:17</td></tr>
 				<tr><td><a href="tips.md">tips.md</a></td><td data-value="174" data-type="int">174 B</td><td>2021-01-17 06:20:02</td></tr>
 				<tr><td><a href="tuple_truth_table.txt">tuple_truth_table.txt</a></td><td data-value="792" data-type="int">792 B</td><td>2021-01-17 06:20:02</td></tr>
-				<tr><td><a href="unix-defects">unix-defects</a></td><td data-value="4912" data-type="int">4 912 B</td><td>2023-03-08 22:29:32</td></tr>
+				<tr><td><a href="unix-defects">unix-defects</a></td><td data-value="5785" data-type="int">5 785 B</td><td>2023-03-13 21:22:22</td></tr>
 				<tr><td><a href="zfs">zfs</a></td><td data-value="1262" data-type="int">1 262 B</td><td>2021-01-17 06:20:02</td></tr>
 			</tbody>
 			</table>
diff --git a/notes/unix-defects.xhtml b/notes/unix-defects.xhtml
@@ -62,6 +62,17 @@
 				Compare this to Haiku
 			</p>
 
+			<h3 id="fs_atom">Filesystem lack of transactions</h3>
+			<p>
+				On Unixes, thanks to the lack of grouping writes into transactions (ie. <code>BEGIN … COMMIT</code> in SQL). The only way to get atomicity is to do manual Copy-on-Write: Copy to a temporary location, write there and then rename to the final destination, meaning you need to have full control over it to avoid race-conditions. And for atomicity over multiple files, a common parent directory is needed, otherwise you're in a bad state between the first rename and the last one.
+			</p>
+			<p>It also means:
+				<ul>
+					<li>Can't do safe operating system updates without ignoring the traditional hierarchy or separating in different filesystems (luckily ZFS subvolumes exists)</li>
+					<li>Horribly slow, you need to copy the file(s), even with hardlinking the ones you're not writing to, it takes a very long time</li>
+				</ul>
+			</p>
+
 			<h2>See Also</h2>
 			<ul>
 				<li><a href="https://utcc.utoronto.ca/~cks/space/blog/unix/CLibraryAPIRequiresC">The Unix C library API can only be reliably used from C</a></li>