Re: Add index scan progress to pg_stat_progress_vacuum

+    +/*
+    + * vacuum_worker_init --- initialize this module's shared memory hash
+    + * to track the progress of a vacuum worker
+    + */
+    +void
+    +vacuum_worker_init(void)
+    +{
+    +       HASHCTL     info;
+    +       long        max_table_size = GetMaxBackends();
+    +
+    +       VacuumWorkerProgressHash = NULL;
+    +
+    +       info.keysize = sizeof(pid_t);
+    +       info.entrysize = sizeof(VacProgressEntry);
+    +
+    +       VacuumWorkerProgressHash = ShmemInitHash("Vacuum Progress Hash",
+    +
+                      max_table_size,
+    +
+                      max_table_size,
+    +
+                      &info,
+    +
+                      HASH_ELEM | HASH_BLOBS);
+    +}

+    It seems to me that creating a shmem hash with max_table_size entries
+    for parallel vacuum process tracking is too much. IIRC an old patch
+    had parallel vacuum workers advertise its progress and changed the
+    pg_stat_progress_vacuum view so that it aggregates the results
+    including workers' stats. I think it’s better than the current one.
+    Why did you change that?

+    Regards,

I was trying to avoid a shared memory to track completed indexes, but aggregating stats does not work with parallel vacuums. This is because a parallel worker will exit before the vacuum completes causing the aggregated total to be wrong. 

For example

Leader_pid advertises it completed 2 indexes
Parallel worker advertises it completed 2 indexes

When aggregating we see 4 indexes completed.

After the parallel worker exits, the aggregation will show only 2 indexes completed. 

 --
 Sami Imseih
Amazon Web Services