Custom Scan is a node in the planned statement which helps external providers
to abstract data scan not just for foreign data wrappers but also for regular
relations so you can benefit your version of caching or hardware optimizations.
This sounds like only an abstraction on the data scan layer, but we can use it
as an abstraction for our distributed queries. The only thing we need to do is
to find distributable parts of the query, plan for them and replace them with
a Citus Custom Scan. Then, whenever PostgreSQL hits this custom scan node in
its Vulcano style execution, it will call our callback functions which run
distributed plan and provides tuples to the upper node as it scans a regular
relation. This means fewer code changes, fewer bugs and more supported features
for us!
First, in the distributed query planner phase, we create a Custom Scan which
wraps the distributed plan. For real-time and task-tracker executors, we add
this custom plan under the master query plan. For router executor, we directly
pass the custom plan because there is not any master query. Then, we simply let
the PostgreSQL executor run this plan. When it hits the custom scan node, we
call the related executor parts for distributed plan, fill the tuple store in
the custom scan and return results to PostgreSQL executor in Vulcano style,
a tuple per XXX_ExecScan() call.
* Modify planner to utilize Custom Scan node.
* Create different scan methods for different executors.
* Use native PostgreSQL Explain for master part of queries.
Previously we'd segfault in PQisnonblocking() which, contrary to other
libpq calls, doesn't handle a NULL PQconn (because there'd be no
appropriate return value for that).
cr: @jasonmp85
Delete operation is blocked for any table distributed by hash using master_apply_delete_command. Suggested master_modify_multiple_shards command as a hint.
During later work the transaction debug output will change (as it will
in postgres 10), which makes it hard to see actual changes in the
INSERT ... SELECT ... test. Reduce to DEBUG2 after changing a debug
message to that log level.
This change ignores `citus.replication_model` setting and uses the
statement based replication in
- Tables distributed via the old `master_create_distributed_table` function
- Append and range partitioned tables, even if created via
`create_distributed_table` function
This seems like the easiest solution to #1191, without changing the existing
behavior and harming existing users with custom scripts.
This change also prevents RF>1 on streaming replicated tables on `master_create_worker_shards`
Prior to this change, `master_create_worker_shards` command was not checking
the replication model of the target table, thus allowing RF>1 with streaming
replicated tables. With this change, `master_create_worker_shards` errors
out on the case.
PostgreSQL 9.5.6 and 9.6.2 were released today and broke several tests
by adding TABLESPACE pg_default output to some DDL commands. Fixed all
occurrences.
cr: @anarazel
velioglu
Metin Döşlü
Metin Doslu
Andres Freund
Jason Petersen
Murat Tuncer
Murat Tuncer
Jason Petersen
Joe Nelson
Brian Cloutier
Marco Slot
Marco Slot
Burak Velioglu
Burak Velioglu
Eren Başak
sumedhpathak
Önder Kalacı
Brian Cloutier