Nettleton: Scott0_: you must be across the aisle from domas!
Abels: How does it come up with that number?
Wollmer: Scott0_: count is a special breed on Innodb tables, doesn’t matter if it’s indexed, it does a table scan
Roorda: Wasn’t there a faster way?
Arena: Scott0_: counted b-trees
Dillion: Myisam stores the row count in the header
Manteca: Explain said it uses index though
Walken: Myisam has a very naive implementation of a counted tree
Sweeting: It has just one count
Villacorta: Scott0_: because of MVCC there isn’t just one count
Weiss: Each thread sees it’s own revision
Sieber: So it can’t rely on a global row count
Gottsch: Technically you can maintain counted-btree in mvcc environment too
Mcgilton: As long as counts are implemented as commutative operations
Sattley: Yeah, but I suspect the devs don’t see that as low hanging fruit, their too busy trying to make 5.7/8 fit for you
Mielnicki: Ah so I can specify something in the WHERE and it will count faster?
Neiner: Well, it is hard to implement them in concurrent fashion
Checketts: Scott0_: yes, because it will look for that in the index
Pysher: This is exactly what domas was talking about earlier. His query was doing a full index scan on 100mn+ entries, he got it to perform range scans and reduce the rows touched
Feerst: I wonder if column IS NOT NULL counts 😛
Henington: You have 594mn rows and so Innodb has to walk the ordered indexes to get the count
Dossett: Scott0_: PK can’t be null anyway
Nickas: But im not using the primary key anymore
Jacquot: So it’s a non-starter
Houlberg: Im using the first key in the index
Batun: There is an existing index
Marsingill: Scott0_: that just means you are using an index that’s even bigger than the PK :
Vigorito: So how do I get around this?
Dermody: Umm, don’t use count* to get precise row counts
Wilda: You mean adding up multiple range scans?
Stencil: Pedward: another interesting problem with optimizer
Heap: It ***umes that data is there
Kuning: Time to write another blog post
Pratte: Scott0_: the simple, but potentially naïve and costly approach is to use information_Schema.tables.table_rows
Kilgo: But querying that table can cause locking contention
Obryon: Lets see what that says
Rahimi: Pedward: it isn’t that expensive
Douthit: As well as causing mysql to read in tables
Tsan: Think about it though, I do full dumps nightly
Spingler: Scott0_: I used to have ‘EXPLAIN SELECT * FROM table’ as a dirty method
Christmann: Even if I explain my countid it gives me the total in the index
Bonhomme: Domas: try telling that to people who run those queries a lot and have 500 queries running at the same time, with a table cache of 2k
Dunford: Pedward: depends on stats_on_metadata value I guess
Papranec: What im doing is saving tabular data with each value in a csv as a row
Bou: Its kind of expensive, but allows to pull reports and graph data with lots of flexibility
Shellabarger: Scott0_: show index will give you the cardinality of the primary key, which is the number of rows in the table
Gallargo: Scott0_: are you storing in a CSV table or converting a CSV to an innodb table?
Graciano: Oh wow I’ve never seen the index displayed that way before