Fixes#375
Prior to this change, shard pruning couldn't be done if:
- Table is hash-distributed
- Partition column of is VARCHAR
- Query to be pruned is a subquery
There were two problems:
- A bug in left-side/right-side checks for the partition column
- We were not considering relabeled types (VARCHAR was relabeled as TEXT)
While reading this code last week, it appeared as though there was no
place we ensured that the partition clause actually used equality ops.
As such, I was worried that we might transform a clause such as id < 5
into a constraint like hash(id) = hash(5) when doing shard pruning. The
relevant code seemed to just ensure:
1. The node is an OpExpr
2. With a related hash function
3. It compares the partition column
4. Against a constant
A superficial reading implied we didn't actually make sure the original
op was equality-related, but it turns out the hash lookup function DOES
ensure that for us. So I added a comment.
This change removes the whitelisting check on the WHERE clauses. Note that, before
this change, citus was already allowing all types of nodes with the following
format (i.e., wrap with a boolean test):
* SELECT col FROM table WHERE (ANY EXPRESSION) is TRUE;
Thus, this change is mostly useful for allowing the expressions in the WHERE clause
directly and avoiding "unsupport clause type" errors.
Fixes issue #258
Prior to this change, Citus gives a deceptive NOTICE message when a query
including ANY or ALL on a non-partition column is issued on a hash
partitioned table.
Let the github_events table be hash-distributed on repo_id column. Then,
issuing this query:
SELECT count(*) FROM github_events WHERE event_id = ANY ('{1,2,3}')
Gives this message:
NOTICE: cannot use shard pruning with ANY (array expression)
HINT: Consider rewriting the expression with OR clauses.
Note that since event_id is not the partition column, shard pruning would
not be applied in any case. However, the NOTICE message would be valid
and be given if the ANY clause would have been applied on repo_id column.
Reviewer: Murat Tuncer
All citusdb references in
- extension, binary names
- file headers
- all configuration name prefixes
- error/warning messages
- some functions names
- regression tests
are changed to be citus.
Previously we used, for historical reasons, MessageContext.
That is problematic if a single message from the client
causes a lot of statements to be planned. E.g. for the
copy_to_distributed_table script one insert statement
is planned for each row inserted via COPY, and only freed
when COPY has finished.
This entirely removes any restriction on the type of partitioning
during DML planning and execution. Though there aren't actually any
technical limitations preventing DML commands against append- (or even
range-) partitioned tables, we had initially forbidden this, as any
future stage operation could cause shards to overlap, banning all
subsequent DML operations to partition values contained within more
than one shards. This ended up mostly restricting us, so we're now
removing that restriction.
When two data types have the same binary representation, PostgreSQL may
add an implicit coercion between them by wrapping a node in a relabel
type. This wrapper signals that the wrapped value is completely binary
compatible with the designated "final type" of the relabel node. As an
example, the varchar type is often relabeled to text, since functions
provided for use with text (comparisons, hashes, etc.) are completely
compatible with varchar as well.
The hash-partitioned codepath contains functions that verify queries
actually contain an equality constraint on the partition column, but
those functions expect such constraints to be comparison operations
between a Var and Const. The RelabelType wrapper node causes these
functions to always return false, which bypasses shard pruning.
eren
Andres Freund
Jason Petersen
Onder Kalaci
Murat Tuncer
Metin Doslu
Jason Petersen