ADBDEV-6442: Refactor diskquota local_table_stats_map

[RekGRpth]

Refactor diskquota local_table_stats_map

During initialization, diskquota uses a non-optimal structure for the local
hashmap local_table_stats_map. This leads to increased RAM consumption during
cluster startup. This patch changes the specified structure, making the table
oid the key, and the value an array of sizes by segments. This significantly
reduces the amount of memory consumed. This patch also fixes a small bug with
duplicate oid tables in the active_oids string array in the dispatch_rejectmap
function.

---

Tests are not provided, but you can estimate the hashmap size using the hash_estimate_size function, for example, like this:

diff --git a/src/gp_activetable.c b/src/gp_activetable.c
index 0888c4d..5b7654d 100644
--- a/src/gp_activetable.c
+++ b/src/gp_activetable.c
@@ -954,6 +954,9 @@ load_table_size(HTAB *local_table_stats_map)
 	Portal                    portal;
 	char                     *sql = "select tableid, size, segid from diskquota.table_size";
 
+	elog(WARNING, "DiskQuotaActiveTableEntry = %li", hash_estimate_size(1000*1000*1000, sizeof(DiskQuotaActiveTableEntry)));
+	elog(WARNING, "ActiveTableEntryCombined = %li", hash_estimate_size(1000*1000, offsetof(ActiveTableEntryCombined, tablesize) + (1000 + 1) * sizeof(Size)));
+
 	if ((plan = SPI_prepare(sql, 0, NULL)) == NULL)
 		ereport(ERROR, (errmsg("[diskquota] SPI_prepare(\"%s\") failed", sql)));
 	if ((portal = SPI_cursor_open(NULL, plan, NULL, NULL, true)) == NULL)

that gives

2024-10-10 14:15:23.186300 +05,,,p684028,th1126361536,,,,0,con9,,seg-1,,,,sx1,"WARNING","01000","DiskQuotaActiveTableEntry = 40623489136",,,,,,,0,,"gp_activetable.c",957,
2024-10-10 14:15:23.186315 +05,,,p684028,th1126361536,,,,0,con9,,seg-1,,,,sx1,"WARNING","01000","ActiveTableEntryCombined = 8040421488",,,,,,,0,,"gp_activetable.c",958,

That is, the memory consumption for 1,000,000 tables on a 1000-segment cluster dropped from 38 gigabytes to 7.5 gigabytes.

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It is easier to view the changes with the "Hide whitespace" option enabled.

[RekGRpth]

#34