Merge indexes for reblog on statuses table (#5831)

We added an index for `[account_id, reblog_of_id]`, but we already have a similar index for `reblog_of_id`. Those index will be bigger according to statuses count. For example, `reblog_of_id` index uses 800MB for 10GB statuses table.

So this patch swaps indexed columns like `[reblog_of_id, account_id]`, then it will covers both usage with single index.

Since those index creation may take a while, I've also disabled previous index creation.

1 files changed, 7 insertions, 0 deletions

diff --git a/db/migrate/20171125185353_add_index_reblog_of_id_and_account_to_statuses.rb b/db/migrate/20171125185353_add_index_reblog_of_id_and_account_to_statuses.rb
new file mode 100644
index 000000000..37662eaa5
--- /dev/null
+++ b/db/migrate/20171125185353_add_index_reblog_of_id_and_account_to_statuses.rb
@@ -0,0 +1,7 @@
+class AddIndexReblogOfIdAndAccountToStatuses < ActiveRecord::Migration[5.1]
+  disable_ddl_transaction!
+
+  def change
+    add_index :statuses, [:reblog_of_id, :account_id], algorithm: :concurrently
+  end
+end