Use in_batches.destroy_all instead of destroy_all

[alpaca-tc]

What is different?
Example for suspending account with huge follows.

• destroy_all
  • It locks all of associated records until complete deleting them. Therefore associated followers can not update Account of themselves for a while.
  • It loads all records at the first. It is very heavy.
• in_batches.destroy_all
  • It locks and releases for each record while saving.
  • It works with a batch of records.

Before association.destroy_all

SELECT "follows".* FROM "follows" WHERE "follows"."account_id" = $1  [["account_id", 2]]

BEGIN
  SELECT  "notifications".* FROM "notifications" WHERE "notifications"."activity_id" = $1 AND "notifications"."activity_type" = $2 LIMIT $3  [["activity_id", 1], ["activity_type", "Follow"], ["LIMIT", 1]]
  DELETE FROM "follows" WHERE "follows"."id" = $1  [["id", 1]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 2], ["LIMIT", 1]]
  UPDATE "accounts" SET "following_count" = COALESCE("following_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 2]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 3], ["LIMIT", 1]]
  UPDATE "accounts" SET "followers_count" = COALESCE("followers_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 3]]

  SELECT  "notifications".* FROM "notifications" WHERE "notifications"."activity_id" = $1 AND "notifications"."activity_type" = $2 LIMIT $3  [["activity_id", 2], ["activity_type", "Follow"], ["LIMIT", 1]]
  DELETE FROM "follows" WHERE "follows"."id" = $1  [["id", 2]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 2], ["LIMIT", 1]]
  UPDATE "accounts" SET "following_count" = COALESCE("following_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 2]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 4], ["LIMIT", 1]]
  UPDATE "accounts" SET "followers_count" = COALESCE("followers_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 4]]

  ...
COMMIT

After association.in_batches.destroy_all

SELECT  "follows"."id" FROM "follows" WHERE "follows"."account_id" = $1 ORDER BY "follows"."id" ASC LIMIT $2  [["account_id", 2], ["LIMIT", 1000]]
SELECT "follows".* FROM "follows" WHERE "follows"."account_id" = $1 AND "follows"."id" IN (1, 2, ...)  [["account_id", 2]]

BEGIN
  SELECT  "notifications".* FROM "notifications" WHERE "notifications"."activity_id" = $1 AND "notifications"."activity_type" = $2 LIMIT $3  [["activity_id", 1], ["activity_type", "Follow"], ["LIMIT", 1]]
  DELETE FROM "follows" WHERE "follows"."id" = $1  [["id", 1]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 2], ["LIMIT", 1]]
  UPDATE "accounts" SET "following_count" = COALESCE("following_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 2]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 3], ["LIMIT", 1]]
  UPDATE "accounts" SET "followers_count" = COALESCE("followers_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 3]]
COMMIT

BEGIN
  SELECT  "notifications".* FROM "notifications" WHERE "notifications"."activity_id" = $1 AND "notifications"."activity_type" = $2 LIMIT $3  [["activity_id", 2], ["activity_type", "Follow"], ["LIMIT", 1]]
  DELETE FROM "follows" WHERE "follows"."id" = $1  [["id", 2]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 2], ["LIMIT", 1]]
  UPDATE "accounts" SET "following_count" = COALESCE("following_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 2]]
  SELECT  "accounts".* FROM "accounts" WHERE "accounts"."id" = $1 LIMIT $2  [["id", 4], ["LIMIT", 1]]
  UPDATE "accounts" SET "followers_count" = COALESCE("followers_count", 0) - 1 WHERE "accounts"."id" = $1  [["id", 4]]
COMMIT
...