Hi Jan, Just a follow up on my previous email. I understood that simply changing the setting for innodb_compression_algorithm would not change any existing tables. Between each test I was running the employees.sql script from the example database. This contains the following sql at the start of the script…. DROP TABLE IF EXISTS dept_emp, dept_manager, titles, salaries, employees, departments; So I definitely think there’s something up here. I’ve performed a similar set of tests below… SET GLOBAL innodb_compression_algorithm=none; source employees.sql du –sh /var/lib/mysql/employees – 385M <- Note all tables are created here with the PAGE_COMPRESSED=1 option. INNODB_SYS_TABLESPACES shows all are Barrcacuda/Dynamic Next I run the ALTER TABLE … ROW_FORMAT=COMPRESSED PAGE_COMPRESSED=DEFAULT; for each table in the employees database du –sh /var/lib/mysql/employees – 135MB; <- Expected 119MB here, probably due to a log file. SET GLOBAL innodb_compression_algorithm=zlib <- After each compression algorithm change I run alter for each tables as above du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=lzo <- Alter run du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=lz4 <- Alter run… du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=lzma <- alter run du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=bzip2 < alter run du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=snappy <- alter run du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_use_trim=1; # Now set trim and run above tests again SET GLOBAL innodb_compression_algorithm=zlib # Again the alter table statements are executed as above du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=lzo du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=lz4 du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=lzma du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=bzip2 du –sh /var/lib/mysql/employees – 119MB SET GLOBAL innodb_compression_algorithm=snappy du –sh /var/lib/mysql/employees – 119MB Recreating the database without the PAGE_COMPRESSED=1 options, then run ALTER TABLE … ROW_FORMAT=COMPRESSED results in a database size of 119MB. When I attempt the compression without ROW_FORMAT=COMPRESSED I get the same results as I previously poste, i.e. no difference in db size apart from when using lzma. Cheers, Rhys From: Jan Lindström [mailto:jan.lindstrom@mariadb.com] Sent: 14 May 2015 06:14 To: Rhys Campbell Cc: maria-discuss@lists.launchpad.net Subject: Re: [Maria-discuss] Innodb Page Compression On Wed, May 13, 2015 at 6:00 PM, Rhys Campbell <Rhys.Campbell@tradingscreen.com<mailto:Rhys.Campbell@tradingscreen.com>> wrote: 1. Why when trim is not used is the db size unchanged apart from lzma? SET GLOBAL innodb_compression_algorithm effects only new tables, it does not change existing tables. If you want to change compression algorithm for existing table you need to do: SET GLOBAL innodb_compression_algorithm = lzo; CREATE TABLE t1 (a int not null primary key, b char(200)) engine=innodb page_compressed =1; -- uses lzo SET GLOBAL innodb_compression_algorithm = lz4; -- no change to existing tables ALTER TABLE t1 ENGINE=InnoDB; -- noe table t1 uses compression algorithm lz4; 2. Why is the compressed size the same for all algorithms? Is the correct algorithm being used? No 3. Can I confirm which algorithm has been used for a page. I can’t see anything in information_schema Not really at the moment, I need to think about adding support for this. 4. Status variables / info schema not working? Status variables work only if pages are really compressed or decompressed see 1) 5. ALTER TABLE … PAGE_COMPRESSED = 1 doesn’t work. Must I always do a full dump & load to enable page compression? You have incorrect syntax. ALTER TABLE departments ROW_FORMAT=COMPRESSED means legacy row-compression and if departments table is page compressed you need to specify ALTER TABLE departments ROW_FORMAT=COMPRESSED PAGE_COMPRESSED=DEFAULT; 6. Lzma/9 compression is not that impressive. Is it meant to rival tokudb? (converting to tokudb results in a db size of ~ 54MB and this includes logs!) See 1) tokudb might use different version of lzma as they use bundled one. R: Jan