Hi Ammit, On Wed, 1 Mar 2017 11:14:15 +0900 Amit Langote <langote_amit...@lab.ntt.co.jp> wrote:
> Nagata-san, > > On 2017/02/28 23:33, Yugo Nagata wrote: > > Hi all, > > > > Now we have a declarative partitioning, but hash partitioning is not > > implemented yet. Attached is a POC patch to add the hash partitioning > > feature. I know we will need more discussions about the syntax and other > > specifications before going ahead the project, but I think this runnable > > code might help to discuss what and how we implement this. > > Great! Thank you! > > > * Description > > > > In this patch, the hash partitioning implementation is basically based > > on the list partitioning mechanism. However, partition bounds cannot be > > specified explicitly, but this is used internally as hash partition > > index, which is calculated when a partition is created or attached. > > > > The tentative syntax to create a partitioned table is as bellow; > > > > CREATE TABLE h (i int) PARTITION BY HASH(i) PARTITIONS 3 USING hashint4; > > > > The number of partitions is specified by PARTITIONS, which is currently > > constant and cannot be changed, but I think this is needed to be changed in > > some manner. A hash function is specified by USING. Maybe, specifying hash > > function may be ommitted, and in this case, a default hash function > > corresponding to key type will be used. > > > > A partition table can be create as bellow; > > > > CREATE TABLE h1 PARTITION OF h; > > CREATE TABLE h2 PARTITION OF h; > > CREATE TABLE h3 PARTITION OF h; > > > > FOR VALUES clause cannot be used, and the partition bound is > > calclulated automatically as partition index of single integer value. > > > > When trying create partitions more than the number specified > > by PARTITIONS, it gets an error. > > > > postgres=# create table h4 partition of h; > > ERROR: cannot create hash partition more than 3 for h > > Instead of having to create each partition individually, wouldn't it be > better if the following command > > CREATE TABLE h (i int) PARTITION BY HASH (i) PARTITIONS 3; > > created the partitions *automatically*? > > It makes sense to provide a way to create individual list and range > partitions separately, because users can specify custom bounds for each. > We don't need that for hash partitions, so why make users run separate > commands (without the FOR VALUES clause) anyway? We may perhaps need to > offer a way to optionally specify a user-defined name for each partition > in the same command, along with tablespace, storage options, etc. By > default, the names would be generated internally and the user can ALTER > individual partitions after the fact to specify tablespace, etc. I though that creating each partition individually is needed because some user will want to specify a tablespce to each partition. However, as you say, that isn't need for many cases because use can move a partition to other tablespaces afterward by ALTER. Thanks, Yugo Nagata > > Thanks, > Amit > > > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers -- Yugo Nagata <nag...@sraoss.co.jp> -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
