[Postgres-xl-developers] Ticket #13 Allow custom distribution functions
petr.chmelar at greycortex.com
Wed Aug 31 07:41:19 PDT 2016
we would like to migrate from pgpool-II to Postgres-XL, since their
parallel mode become obsolete
in version 3.5.
The main issue for us is that we must use geographically distributed
architecture and the lines interconnecting them are not always suitable
for DISTRIBUTE BY alternatives you provide. We need PLpg/SQL or plain
SQL function like "prefer_local" so the Coordinator may be able to
determine the exact location of target row from incoming statement.
Thus, we propose to develop the extension within GreyCortex.
We have investigated the possibility to add the locate_whatever_insert
and locate_whatever_select functions into src/include/pgxc/locator.h and
src/backend/pgxc/locator/locator.c and we have the following questions:
* How to modify your SQL modifications, eg. DISTRIBUTE BY
* What is the difference between DISTRIBUTE BY and DISTRIBUTED - it is
not well explained in
however it seems to use HASH by default.
* How is it possible to pass the custom function name to the functions
according to your SQL modifications? Can we use name or
regprocedure/regproc (pg_proc), please?
We have also identified a show stopper concerning our deployment of
PgXL. According to
http://files.postgres-xl.org/documentation/queries-with.html you can do:
EXECUTE DIRECT ON (datanode_1)
'WITH deleted AS (
DELETE FROM ONLY table
WHERE timestamp < now()
However, it says both with or without EXECUTE DIRECT on both Node and
ERROR: INSERT/UPDATE/DELETE is not supported in subquery
We have found this in the planner.c (#ifdef XCP if (root->query_level >
1) ereport ...). Does this mean PgXL doesn't support subqueries somehow?
So, the questions are:
* Can we use standard PostgreSQL for data nodes, please?
* Otherwise, can we allow INSERT/UPDATE/DELETE in subquery in case we
perform this on a Node only?
* Can we discuss our involvement in the development via Skype or
* Or should we contact someone from 2ndQuadrant, please?
We'll be happy to join the community. Thank you and cheers,
DB Developer, GreyCortex
+420 602 54 2468
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