Re: Table Partitioning Feature

Hi Emmanuel,

We are considering to following approach:
1. metadata table pg_partitions is defined as follows:
CATALOG(pg_partitions,2336) BKI_WITHOUT_OIDS
{
Oid partrelid; // partition table Oid
Oid parentrelid; // Parent table Oid
int4 parttype; // Type of partition, list, hash, range
Oid partkey; // partition key Oid
Oid keytype; /// type of partition key.
int4 keyorder /// order of the key in multi-key partitions.
text min;
text max; // min and max for range parti
text[] list;
int hash; // hash value
} FormData_pg_partitions;

2. C triggers will fire a query on this table to get the relevant
partition of the inserted/updated data using SPI interface. The query
will look something like (for range partitioning)

select min(partrelid)
from pg_partitions
where parentrelid = 2934 // we know this value
and (
( $1 between to_int(min ) and to_int(max) and
keyorder = 1) OR
($2 between to_date (min) and to_date (max) and
keyorder =2 )
....
)
group by
parentrelid
having
count(*) = <number of partition keys>

$1, $2, ... are the placeholders of the actual partition key values of
trigger tuple.

Since we know the type of partition keys, and the parentrelid, this
kind of query string can be saved in another table say, pg_part_map.
And its plan can be parsed once and saved in cache to be reused.
Do you see any issue with using SPI interface within triggers?

The advantage of this kind of approah is that trigger code can be made
genric for any kind of partition table.

Thanks,
Amit
Persistent Systems,
www.persistentsys.com

On 1/23/09, Emmanuel Cecchet <manu(at)frogthinker(dot)org> wrote:
> Amit,
>
> You might want to put this on the
> http://wiki.postgresql.org/wiki/Table_partitioning wiki
> page.
> How does your timeline look like for this implementation?
> I would be happy to contribute C triggers to your implementation. From what
> I understood in
> http://archives.postgresql.org/pgsql-hackers/2008-01/msg00269.php,
> you already have an implementation that parses the grammar and generates
> rules as if someone had written them. Is this code available?
>
> Regarding the use of triggers to push/move data to partitions, what if
> someone declares triggers on partitions? Especially if you have
> subpartitions, let's consider the case where there is a trigger on the
> parent, child and grandchild. If I do an insert in the parent, the user
> trigger on the parent will be executed, then the partition trigger that
> decides to move to the grandchild. Are we going to bypass the child trigger?
> If we also want fast COPY operations on partitioned table, we could have an
> optimized implementation that could bypass triggers and move the tuple
> directly to the appropriate child table.
>
> Thanks for this big contribution,
> Emmanuel
>
>
> >
> > Hi,
> >
> > We are implementing table partitioning feature to support
> > - the attached commands. The syntax conforms to most of the suggestion
> mentioned in
> http://archives.postgresql.org/pgsql-hackers/2008-01/msg00413.php,
> barring the following:
> > -- Specification of partition names is optional. System will be able to
> generate partition names in such cases.
> > -- sub partitioning
> > We are using pgsql triggers to push/move data to appropriate partitions,
> but we will definitely consider moving to C language triggers as suggested
> by manu.
> > - Global non-partitioned indexes (that will extend all the partitions).
> > - Foreign key support for tables referring to partitioned tables.
> >
> > Please feel free to post your comments and suggestions.
> >
> > Thanks,
> > Amit
> > Persistent Systems
> >
> >
> >
> >
> ------------------------------------------------------------------------
> >
> >
> >
>
>
> --
> Emmanuel Cecchet
> FTO @ Frog Thinker Open Source Development & Consulting
> --
> Web: http://www.frogthinker.org
> email: manu(at)frogthinker(dot)org
> Skype: emmanuel_cecchet
>
>