Search code examples
kdb

How to correctly enum and partition a kdb table?

I put together a few lines to partition my kdb table, which contains string columns of course and thus must to be enumerated.

I wonder if this code is completely correct or if it can be simplified further. In particular, I have some doubt about the need to create a partitioned table schema given the memory table and the disk table will have exactly the same layout. Also, there might be a way to avoid creating the temporary tbl_mem and tbl_mem_enum tables:

...
tbl_mem: select ts,sym,msg_type from oms_mem lj sym_mem;
tbl_mem_enum: .Q.en[`$sym_path] tbl_mem;
delete tbl_mem from `.;

(`$db;``!((17;2;9);(17;2;9))) set ([]ts:`time$(); ticker:`symbol$(); msg_type:`symbol$());
(`$db) upsert (select ts,ticker:sym,msg_type from tbl_mem_enum)
delete tbl_mem_enum from `.;

PS: I know, I shouldn't use "_" to name variables, but then what do I use to separate words in a variable or function name? . is also a kdb function.

Solution

  • I think you mean that your table contains symbol columns - these are the columns that you need to enumerate (strings don't need enumeration). You can do the write and enumeration in a single step. Also if you are using the same compression algo/level on all columns then it may be easier to just use .z.zd:

    .z.zd:17 2 9i;
(`$db) set .Q.en[`$sym_path] select ts, ticker:sym, msg_type from oms_mem lj sym_mem;

    It's generally recommended to use camelCase instead of '_'. Some useful info here: http://www.timestored.com/kdb-guides/q-coding-standards