Hi King,
Thank you for the detailed explanation! Now I understand rollback journal a
bit more.
John Lin
J. King <jk...@jkingweb.ca> 於 2017年11月24日 週五 上午10:28寫道：
> The rollback journal is used to return the database to its previous state
> in the case of a partial write, not complete writes which are interrupted.
> As you didn't commit the transaction, no write occurred, never mind a
> partial one, so the database remained in its initial state.
>
> Deleting a rollback journal is a bad idea. In this case it was harmless,
> but normally it's an excellent way to corrupt your database.
>
> As to where uncommitted transactions live, I am not sure. I'll let someone
> else answer that.
>
> On November 23, 2017 9:13:20 PM EST, "林自均" <johnl...@gmail.com> wrote:
> >Hi folks,
> >
> >When I was learning about rollback journal, I did the following tests:
> >
> >(in shell 1)
> >$ sqlite3 /tmp/db.sqlite
> >SQLite version 3.21.0 2017-10-24 18:55:49
> >Enter ".help" for usage hints.
> >sqlite> PRAGMA journal_mode;
> >delete
> >sqlite> CREATE TABLE bank (name STR, money INT);
> >sqlite> INSERT INTO bank VALUES ("john", 5566);
> >sqlite> BEGIN;
> >sqlite> UPDATE bank SET money = money + 100 WHERE name = "john";
> >sqlite>
> >
> >(then in shell 2)
> >$ kill -kill $(pidof sqlite3) # kills the sqlite3 process in shell 1
> >$ rm -f /tmp/db.sqlite-journal
> >$ sqlite3 /tmp/db.sqlite .dump
> >PRAGMA foreign_keys=OFF;
> >BEGIN TRANSACTION;
> >CREATE TABLE bank (name STR, money INT);
> >INSERT INTO bank VALUES('john',5566);
> >COMMIT;
> >
> >I was expecting that deleting the rollback journal would commit the
> >uncommitted transaction (i.e. increase money from 5566 to 5666).
> >However,
> >it didn't.
> >
> >I also noticed that the md5sum of db.sqlite are the same before the
> >UPDATE
> >query and after it, which means that the UPDATE query doesn't really
> >write
> >into db.sqlite. Does it only write into memory?
> >
> >Thanks for answering my questions.
> >
> >John Lin
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>
> --
> Sent from my Android device with K-9 Mail. Please excuse my brevity.
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