diff options
Diffstat (limited to 'src/backend/optimizer/plan/planner.c')
| -rw-r--r-- | src/backend/optimizer/plan/planner.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index eaee9eda771..3a4e28b5026 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -330,11 +330,13 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions, * functions are present in the query tree. * * (Note that we do allow CREATE TABLE AS, SELECT INTO, and CREATE - * MATERIALIZED VIEW to use parallel plans, but as of now, only the leader - * backend writes into a completely new table. In the future, we can - * extend it to allow workers to write into the table. However, to allow - * parallel updates and deletes, we have to solve other problems, - * especially around combo CIDs.) + * MATERIALIZED VIEW to use parallel plans, but this is safe only because + * the command is writing into a completely new table which workers won't + * be able to see. If the workers could see the table, the fact that + * group locking would cause them to ignore the leader's heavyweight + * GIN page locks would make this unsafe. We'll have to fix that somehow + * if we want to allow parallel inserts in general; updates and deletes + * have additional problems especially around combo CIDs.) * * For now, we don't try to use parallel mode if we're running inside a * parallel worker. We might eventually be able to relax this |