Forgive the bluntness of the statement, but why is anyone even worrying
about transactions as they relate to MySQL???
COMMIT in MySQL is passed to the table handler. In the case of MyISAM
tables, the handler disregards the statement. For InnoDB and BDB tables,
COMMIT acts as it does in PostgreSQL.
So various people in this thread implying that MySQL isn't really a
database need to do some more reading.
In summary, just encapsulate everything in transaction blocks and the
underlaying database will act appropriately.
Regards,
Chris
Aaron Stone wrote:
I don't even know where to begin in terms of designing the delivery chain
around transactions. Could we do it as simply as adding functions...
void db_begin_transaction(void);
void db_flush_transaction(void); (or db_commit_...?)
and then calling these functions before and after each major section of
database code? For the delivery chain, we could do it inside of
insert_message(). For dbmail-smtp, this basically means that the execution of
the whole program is within one transaction. For dbmail-lmtpd, it means that
each message is delivered within a transaction but the miscellaneous queries
before the main message delivery chain are not transacted. For MySQL, these
functions would be noops.
Thing that might work?
Aaron
Thomas Mueller <[EMAIL PROTECTED]> said:
Hi Aaron,
Do you have any way of narrowing this down to specific queries that are
taking the longest and/or are being executed the most? That would
identify which low-level database functions are being called, then we
can just trace our way up the call chain to see who's misbehaving or
acting on a flawed design. Also, if you could run similar tests against
the latest 1.2, it would help to give a frame of reference, particularly
for my delivery chain design.
That's simple: the main design flaw (actually that's no design flaw I
think, that's because the so called database MySQL couldn't do
transactions in the past) is that dbmail doesn't use transaction.
Because of that AutoCommit is used and whenever dbmail does anySqlQuery
Postgres does 'BEGIN; anySqlQuery; COMMIT;' - and that is terribly
slow. To ensure the Durability in ACID the database has to fflush()
every transaction to stable storage!
That's why there is only one solution: we have to use transaction.
With transactions we could remove the integrity checks of
dbmail-maintenance too, because the database guarantees integrity.
Anyway, I did a trace of all SQL queries when a mail is copied using
IMAP. I got 35 SELECT, 4 INSERT, 5 UPDATE (44 db operations to insert
one mail?).
When searching for the sequential scan I found something quite
interesting in the docs: the planer decides for every scan if a seqScan
is cheaper that an index scan, and does a seqScan even if an index
exists:
dbmail=> explain SELECT mailbox_idnr FROM mailboxes WHERE owner_idnr=2;
QUERY PLAN
---------------------------------------------------------
Seq Scan on mailboxes (cost=0.00..1.06 rows=3 width=8)
Filter: (owner_idnr = 2)
(2 rows)
The table has an index on owner_idnr.
So I should repeat this test with a database with several hundred to
thousand user, several dozen mailboxes for each user and several dozen
mails in each mailbox to find out if all required indizes are there.
Did anyone write a script to create such a database?
But I found a strange query:
SELECT mailbox_idnr FROM mailboxes WHERE mailbox_idnr = '4' AND
owner_idnr = '2'
mailbox_idnr is the primary key so that could be optimized to:
SELECT 4
;-)
I don't have a 1.2 installation, I'm sorry.
--
MfG Thomas Mueller - http://www.tmueller.com for pgp key (95702B3B)
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