external
/
citus
mirror of https://github.com/citusdata/citus.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Support PostgreSQL 18’s new RTE kinds in Citus deparser (#8023) 

Fixes #8020 

PostgreSQL 18 introduces two new, *pseudo* rangetable‐entry kinds that
Citus’ downstream deparser must recognize:

1. **Pulled-up shard RTE clones** (`CITUS_RTE_SHARD` with `relid ==
InvalidOid`)
2. **Grouping-step RTE** (`RTE_GROUP`, alias `*GROUP*`, not actually in
the FROM clause)

Without special handling, Citus crashes or emits invalid SQL when
running against PG 18beta1:

* **`ERROR: could not open relation with OID 0`**
Citus was unconditionally calling `relation_open(rte->relid,…)` on
entries whose `relid` is 0.
* **`ERROR: missing FROM-clause entry for table "*GROUP*"`**
Citus’ `set_rtable_names()` assigned the synthetic `*GROUP*` alias but
never printed a matching FROM item.

This PR teaches Citus’ `ruleutils_18.c` to skip catalog lookups for RTEs
without valid OIDs and to suppress the grouping-RTE alias, restoring
compatibility with both PG 17 and PG 18.

---

## Background

* **Upstream commit
[[247dea8](247dea89f7)**
Introduced `RTE_GROUP` for the grouping step so that multiple subqueries
in `GROUP BY`/`HAVING` can be deduplicated and planned correctly.
* **Citus PR
[[#6428](https://github.com/citusdata/citus/pull/6428)](https://github.com/citusdata/citus/pull/6428)**
Added initial support for treating shard RTEs like real
relations—calling `relation_open()` to pick up renamed-column fixes.
Worked fine on PG 11–17, but PG 18’s pull-up logic clones those shard
RTEs with `relid=0`, leading to OID 0 crashes.

---

## Changes

1. **Guard `relation_open()`**
In `set_relation_column_names()`, only call `relation_open(rte->relid,
…)` when

   ```c
   OidIsValid(rte->relid)
   ```

Prevents the “could not open relation with OID 0” crash on both
pulled-up shards and synthetic RTEs.

2. **Handle pulled-up shards** (`CITUS_RTE_SHARD` with `relid=0`)
Copy column names directly from `rte->eref->colnames` instead of hitting
the catalog.

3. **Handle grouping RTE** (`RTE_GROUP`)

* **In `set_relation_column_names()`**: fallback to
`rte->eref->colnames` for `RTE_GROUP`.
   * **In `set_rtable_names()`**: explicitly assign

     ```c
     refname = NULL;  /* never show *GROUP* in FROM */
     ```

     so that no `*GROUP*` alias is ever printed.

   **Why this is required:**
PostgreSQL 18’s parser now represents the grouping step with a synthetic
RTE whose alias is always `*GROUP*`—and that RTE is **never** actually
listed in the `FROM` clause. If Citus’ deparser assigns and emits
`*GROUP*` as a table reference, the pushed-down SQL becomes:

   ```sql
SELECT *GROUP*.mygroupcol … -- but there is no “*GROUP*” in the FROM
list
   ```

   Workers then fail:

   ```
   ERROR: missing FROM-clause entry for table "*GROUP*"
   ```

By setting `refname = NULL` for `RTE_GROUP` in `set_rtable_names()`, the
deparser prints just the column name unqualified, exactly matching
upstream PG 18’s behavior and yielding valid SQL on the workers.

4. **Maintain existing behavior on PG 15–17**

* Shard RTEs *with* valid `relid` still open the catalog to pick up
renamed-column fixes.
   * No impact on other RTE kinds or versions prior to PG 18.

---
pull/8030/head^2
Mehmet YILMAZ 2025-07-17 13:15:31 +03:00 committed by GitHub
parent 5005be31e6
commit da24ede835
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
1 changed files with 30 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
src/backend/distributed/deparser/ruleutils_18.c
View File

@ -795,6 +795,11 @@ set_rtable_names(deparse_namespace *dpns, List *parent_namespaces,
/* Unnamed join has no refname */
refname = NULL;
}
else if (rte->rtekind == RTE_GROUP)
{
/* Use the name of the group */
refname = NULL;
}
else
{
/* Otherwise use whatever the parser assigned */
@ -1191,8 +1196,9 @@ set_relation_column_names(deparse_namespace *dpns, RangeTblEntry *rte,
* real_colnames[] will be indexed by physical column number, with NULL
* entries for dropped columns.
*/
if (rte->rtekind == RTE_RELATION ||
GetRangeTblKind(rte) == CITUS_RTE_SHARD)
if ((rte->rtekind == RTE_RELATION ||
GetRangeTblKind(rte) == CITUS_RTE_SHARD) &&
OidIsValid(rte->relid))
{
/* Relation --- look to the system catalogs for up-to-date info */
Relation rel;
@ -1214,6 +1220,28 @@ set_relation_column_names(deparse_namespace *dpns, RangeTblEntry *rte,
real_colnames[i] = pstrdup(NameStr(attr->attname));
}
relation_close(rel, AccessShareLock);
}
else if (GetRangeTblKind(rte) == CITUS_RTE_SHARD)
{
/* shard RTE without relid (pulled-up clone in PG18) */
/* use the column aliases already stored in rte->eref->colnames */
ncolumns = list_length(rte->eref->colnames);
real_colnames = (char **) palloc0(ncolumns * sizeof(char *));
for (i = 0; i < ncolumns; i++)
real_colnames[i] = pstrdup(strVal(list_nth(rte->eref->colnames, i)));
/* keep changed_any / has_anonymous defaults */
}
else if (rte->rtekind == RTE_GROUP)
{
/* ----- synthetic PG 18 RTE for GROUP BY / HAVING ----- */
ncolumns = list_length(rte->eref->colnames);
real_colnames = (char **) palloc0(ncolumns * sizeof(char *));
for (i = 0; i < ncolumns; i++)
real_colnames[i] = pstrdup(strVal(list_nth(rte->eref->colnames, i)));
}
else
{