DESCRIPTION: Avoid query deparse and planning of shard query in local execution. Adds citus.enable_local_execution_local_plan GUC to allow avoiding unnecessary query deparsing to improve performance of fast-path queries targeting local shards.
If a fast path query resolves to a shard that is local to the node planning the query, a shortcut can be taken so that the OID of the shard is plugged into the parse tree, which is then planned by Postgres. In `local_executor.c` the task uses that plan instead of parsing and planning a shard query. How this is done: The fast path planner identifies if the shortcut is possible, and then the distributed planner checks, using `CheckAndBuildDelayedFastPathPlan()`, if a local plan can be generated or if the shard query should be generated.
This optimization is controlled by a GUC `citus.enable_local_execution_local_plan` which is on by default. A new
regress test `local_execution_local_plan` tests both row-sharding and schema sharding. Negative tests are added to
`local_shard_execution_dropped_column` to verify that the optimization is not taken when the shard is local but there is a difference between the shard and distributed table because of a dropped column.
With this commit we've started to propagate sequences and shell
tables within the object dependency resolution. So, ensuring any
dependencies for any object will consider shell tables and sequences
as well. Separate logics for both shell tables and sequences have
been removed.
Since both shell tables and sequences logic were implemented as a
part of the metadata handling before that logic, we were propagating
them while syncing table metadata. With this commit we've divided
metadata (which means anything except shards thereafter) syncing
logic into multiple parts and implemented it either as a part of
ActivateNode. You can check the functions called in ActivateNode
to check definition of different metadata.
Definitions of start_metadata_sync_to_node and citus_activate_node
have also been updated. citus_activate_node will basically create
an active node with all metadata and reference table shards.
start_metadata_sync_to_node will be same with citus_activate_node
except replicating reference tables. stop_metadata_sync_to_node
will remove all the metadata. All of those UDFs need to be called
by superuser.
With local query caching, we try to avoid deparse/parse stages as the
operation is too costly.
However, we can do deparse/parse operations once per cached queries, right
before we put the plan into the cache. With that, we avoid edge
cases like (4239) or (5038).
In a sense, we are making the local plan caching behave similar for non-cached
local/remote queries, by forcing to deparse the query once.
Colm
Burak Velioglu
Onder Kalaci