While reading Baron’s take on 5.1, I saw Mark‘s comment and part of it stuck with me:
And this is a huge problem when you run replication over a flaky network.
When you have a probability of error, there is a number of machines you can run to ensure you *always* have a failure. This number of machines is much less than you think.
How?
Seriously, how do I do this?
Following constraints: T1000 has no local DVD drive. No other Solaris hosts on network.
(Note that it takes about 15 seconds to find the Debian install instructions. “Put this file on tftp server, boot.”)
In what situation will this succeed:
ALTER TABLE t1 RENAME t2;
but this fail:
RENAME TABLE t1 TO t2;
?
Highlight the white text below for the answer:
When t1 is a temporary table.
Wow… I wonder why that is, I can’t think of any good reason…
Using the wonderful bittorrent, I got the CD image in next to no time (in contrast to the Solaris Express image I’m currently downloading via HTTP that’s taking forever).
Boot time in VirtualBox (off the ISO image) was rather quick, usual questions on keyboard layout and desired language (it’d be neater if these were GUI questions… but anyway). The GNOME desktop loaded up, popup window informed me that it had connected to the network. Awesome.
Package manager: opend quickly, using the opensolaris.org repository and it does seem to have a lot of packages… even MySQL 5.0.67 (and 4.0.24). Not 5.1 though, but it is early days (and it was just released as GA the other day).
At least one unusual thing was SUNWgrub and SUNWgrubS (where the S is for source). I assume this is some packaging oddity as I don’t ese other packages like this.
SUNWii wins the odd package name award.
The Time Slider seems like possibly the most awesome thing ever. It periodically takes ZFS snapshots of your disk and presents you with a time slider in nautilus so you can just view your data how it was in the past (at previous snapshots).
I can’t see how to change the keyboard layout to DVORAK (at least while booted off the CD image).
The getting started guide also shows how to get a development environment going… this is quite promising. Will do proper install shortly and do a step by step “building drizzle on OpenSolaris 2008.11” post.
The other day I ordered some soap nuts from Green And Nutty – and they arrived (rather quickly) yesterday (or today… I forget.. a package on the doorstep anyway). Kristy (owner) was telling me about the soap nuts ages ago… and I finally got around to giving them a go (otherwise known as “stewart put two and two together when needing to buy washing powder”).
I don’t have an allergy problem to normal soaps and aren’t on some exotic “everything must be natural” trip (although it does have a certain appeal).
One bonus thing (for me) is that I *know* that what I’m using for washing clothes is vegan.
Anyway, first wash with them today and no problems to report. Seemed to produce clean clothes (although weren’t that dirty to begin with). Will report further in future washes.
There’s a 2-for-1 offer for December which I took (1kg for $17.99)… which should be enough to last a year (for the average household… and I’m smaller than that).
What would you expect the following to fail with?
CREATE TABLE t1 (a int, b int);
insert into t1 values (100,100);
CREATE TEMPORARY TABLE t2 (a int, b int, primary key (a));
BEGIN;
INSERT INTO t2 values(100,100);
CREATE TEMPORARY TABLE IF NOT EXISTS t2 (primary key (a)) select * from t1;
If you answered ER_DUP_ENTRY then you are correct.
If you use IF NOT EXISTS in a CREATE TABLE ... SELECT statement, any rows selected by the SELECT part are inserted regardless of whether the table already exists.
Does anybody else find this behaviour “interesting”?
Sadly, after many years of service (over 5), my Microsoft VisualStudio.net bottle opener is no longer functional enough to keep on my keyring. See image below for the arrow pointing to where too much metal has chipped off that it no longer can open all beer.
It is a sad day.
Luckily, I have another one I can quickly add to my keyring to facilitate beer opening when needed.
Well… there’s:
(both of these are quite obvious).
But then you have:
Well… two types of temporary tables:
You may have seen these “#sql-foo.frm” etc files around.
but you can also CREATE TABLE `#sql-foo` (you know, because that’s a good string to use in your app). In fact, you can (and shouldn’t) create a table with the exact same name as the temporary #sql table and use it in your app.
So really the primary key for a table is: string database name, string table name, bool is_tmp. Oh, and the /tmp/ temporary tables just to screw with your braiiiinn.
In drizzle, this is what the storage engine API is ending up looking like. It’s the responsibility of the engine to encode the temporary table names so that they don’t clash with the non-temporary table names. This could be done by putting them in a different set of files, marking them with som eflag, or just passing the is_tmp flag to build_table_filename (or make_table_key) and being done with it.
I think this ends up being the least-hacky approach and it does mean we can remove the bass ackwards if(table_name[0]==’#’) checks from some engines.
totally jealous of this gift.. how awesome would it be to have that… mmmm…
FAIL:
WIN:
Putting on laundry in FAIL mode is quite fail. luckily didn’t have anything on floor and my washing machine doesn’t use much water.
Real noisy fucker. So loud, that if it’s in the garage but the back door is open, I still hear it.
Being used for drizzle dev on Solaris… although a switch to OpenSolaris or Linux is likely imminent. Straight Solaris 10 is just too annoying.
Well… nearly any engine.
I have a plan forming in my head to add some hooks to engines to help with creating temporary tables (the ones created while executing a query, not ones created during ALTER TABLE).
Currently, if you ALTER TABLE and we require a temporary table, it’s still database.table but we generate a table name that’s small, unique and begins with “#sql”.
I’ve changed some of the handler interface to accept two strings (database name, table name) instead of one “path” that may (or may not) end in “.FRM” and may (or may not) begin with “./” and may (or may not) use the “/” separator between database and table name (hint: on win32, it’s sometimes “”).
So ha_delete_table is now: ha_delete_table(db, table_name). Sanity!
(this has the downside of being a incompatible change that doesn’t break the build as there seems to be no way in C++ to say “derived classes cannot implement a function of this name”).
This is annoying for temporary tables however.
They don’t reside in a database… they’re off in la-la land (otherwise known as opt_drizzle_tmpdir).
Now… in MySQL 5.1 the ability for multiple temporary directories was added, and the MySQL server will cycle through them. The clusterfuck part of this was that a mutex was added… so every time the code goes to get the name of a (or for 99.99999999% of cases, the) temporary directory, it has to grab a mutex. With modern systems being able to have *many* simultaneous IO operations (e.g. create files) this is just dumb. It’s gone.
If you want to use multiple spindles for temporary tables it’s called RAID people (or buy an SSD, mkfs.ext2 it and just wipe it on reboot. simple.)
Anyway… back to temporary tables:
they’re in /tmp or something. So an API that’s foo(const char *db, const char *table_name) doesn’t work as well.
Also, for a bunch of engines, it’s good to know that you’re using a temporary table. You probably want to store these somewhere that never needs fsync() or anything like that. If the server goes away, these tables are *gone*. So optimise for that.
Heck, it may even be good to store temporary tables in your distributed engine (if that engine is memory based) as it’s often faster to access remote memory than local disk (although with SSD this is a whole different ball game… in fact, I’m not sure if it’s even still a ball game.. it’s possibly frisbee)
But currently there’s hardcoded a mi_create (MyISAM create) call in the server and in the 6.0-maria tree, an #ifdef around if it’s mi_create or maria_create.
So not any engine yet… but one can dream. Yes, I dare to dream.
(although why I was dreaming of a small board with a PowerPC 603, 8MB RAM and a mini DVI port the other night is quite beyond me)
They are wrong.
Misleading at best.
Reworking parts of Drizzle (which came directly from MySQL) it can get painfully obvious. Things like “afaiu” and “???” appear in more than one place (that is if the comment isn’t just obviously wrong).
A comment merely states what one person thought the code did at some point in the past. It has no relation to what the code actually does now.
From ha_myisam.cc:
/*
TODO: switch from protocol to push_warning here. The main reason we didn’t
it yet is parallel repair. Due to following trace:
mi_check_print_msg/push_warning/sql_alloc/my_pthread_getspecific_ptr.
Also we likely need to lock mutex here (in both cases with protocol and
push_warning).
*/
protocol->prepare_for_resend();
protocol->store(name, length, system_charset_info);
protocol->store(param->op_name, system_charset_info);
protocol->store(msg_type, system_charset_info);
protocol->store(msgbuf, msg_length, system_charset_info);
if (protocol->write())
sql_print_error(“Failed on my_net_write, writing to stderr instead: %s\n”,
msgbuf);
return;
Hopefully this will serve as a good TODO list to go and fix at some point.
If you went “wtf” at The Drizzle Snowman – WIN! – Jay Pipes on PlanetMySQL suddenly ending at “create table”, you should click through and see the unicode character for a snowman.
In other fun, we’ve also created tables with the name of cloud symbol, umbrella symbol and umbrella with rain drops symbol. All of these seem rather appropriate for Drizzle.
It’s the FRM file format version number.
It’s not the version of the table as one might expect (i.e. after CREATE it’s 1. Then, if you ALTER, it’s 2. Alter again 3 etc).
In Drizzle, we now return 0.
In future, I plan that Drizzle will allow the engine to say what version it is (where 0 is “dunno”).
This’ll be a good step towards being able to cope with multiple versions of a table in use at once (and making sense of this to the user).
So… in removing the FRM file in Drizzle, I found a bit of a nugget on how drop table works (currently in the MySQL server and now “did” in Drizzle).
If you DROP TABLE t1; this is what happens
I do like the “probably”.
Oh, and on a “storage engine api” front, some places seem to expect handler::delete_table(const char* name) to return ENOENT on table not existing. In reality however:
fputs(“Â InnoDB: Error: table “, stderr);
ut_print_name(stderr, trx, TRUE, name);
fputs(” does not exist in the InnoDB internaln”
“InnoDB: data dictionary though MySQL is”
” trying to drop it.n”
“InnoDB: Have you copied the .frm file”
” of the table to then”
“InnoDB: MySQL database directory”
” from another database?n”
“InnoDB: You can look for further help fromn”
“InnoDB: http://dev.mysql.com/doc/refman/5.1/en/”
“innodb-troubleshooting.htmln”,
stderr);
and just to add to the fun, elsewhere in the code, a access(2) call on the frm file name is used to determine if the table exists or not.
The road to removing the FRM has all sorts of these weird-ass things along it. Kinda nice to be able to replace this with something better (and, hopefully – good).
But let me sum up with sql_table.cc:
“This code is wrong and will be removed, please do not copy.”
Scaling MySQL on a 256-way T5440 server using Solaris ZFS and Java 1.7
*cough*
(and then wipe coffee off the computer)
of course the real aim should be to scale with one instance on the machine as scaling with multiple instances on the one machine isn’t scaling at all – it’s scale out, but with more problems (now when one machine goes down, so do 1110202434 database instances).
from elliot: phrase from nearest book
My result:
“A lot of UN staff call themselves human rights experts but need a shoulder to cry on each time there’s a killing”
– Emergency Sex (and other desperate measures)
Kenneth Cain, Heidi Postlewait and Andrew Thomson
In 2 years (ish):
In 5 years:
That’s all for now…