FYI, I documented better the peculiarity AndyS
noticed and emailed mariaDB team, see below
Jacek
-------- Original Message --------
Subject: myisam - unexpected file size and myisamchk behavior
Date: Thu, 20 Feb 2014 17:58:58 -0800
From: Jacek Becla <[log in to unmask]>
Organization: SLAC National Accelerator Laboratory
To: [log in to unmask] <[log in to unmask]>, [log in to unmask]
<[log in to unmask]>
Hello,
I run into something puzzling when testing 10.0.8.
In essence, I created several 250-million-row MyISAM
tables with different number of columns each by
running something like:
CREATE TABLE x50 AS
SELECT <50 columns here>
FROM <huge table>
LIMIT 25000000;
mysqldump x50 > x50.dump
mysql t < x50.dump
create table x40 as select <40 columns here> from x50;
create table x30 as select <30 columns here> from x40;
create table x20 as select <20 columns here> from x30;
create table x10 as select <10 columns here> from x30;
create table x05 as select < 5 columns here> from x10;
create table x04 as select < 4 columns here> from x05;
create table x03 as select < 3 columns here> from x04;
create table x02 as select < 2 columns here> from x03;
create table x01 as select < 1 column here> from x02;
size of the 50-column table is very puzzling:
columns MYD
[bytes]
50 5,613,095,416
40 7,925,000,000
30 5,900,000,000
20 3,875,000,000
10 1,825,000,000
5 825,000,000
4 725,000,000
3 525,000,000
2 425,000,000
1 225,000,000
Also, when I try running myisamchk, it runs (as expected)
for a minute or so, showing the row counter as usually,
and prints:
Data records: 25000000 Deleted blocks: 0
- check file-size
- check record delete-chain
- check key delete-chain
- check index reference
- check record links
while running it on any other table returns immediately with
Data records: 25000000 Deleted blocks: 0
- check file-size
- check record delete-chain
- check key delete-chain
- check index reference
(notice, there is no "check record links")
The actual commands I run are described here:
https://dev.lsstcorp.org/trac/wiki/db/tests/MySql/AriaVsMyISAM
Same thing happens when I try to reproduce it on much small
table. In case you want to reproduce it, the contents of
the two small tables can be found at:
http://www.slac.stanford.edu/~becla/tmp/myisamTest.tar.gz
Does anyone understand why we are seeing this unusual
behavior?
Thanks
Jacek
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