为什么此查询的仅索引扫描速度较慢？

Question

这里是解释/缓冲输出：https://explain.depesz.com/s/lOHQ

这是我的疑问：

q = (g.session.query(Email)
         .join(CampaignRecipient, and_(CampaignRecipient.email_id == Email._id,
                                       CampaignRecipient.campaign_id == campaign._id))
         .join(MailMergeSentLog, and_(MailMergeSentLog.email_id == Email._id,
                                      MailMergeSentLog.mail_merge_id == campaign._id))
         .join(PreviousStage, PreviousStage._id == MailMergeSentLog.mail_merge_stage_id)
         .filter(~Email._id.in_(alr_sent_subq))
         .filter(~Email._id.in_(sent_exclusion_subq))
         .filter(~Email._id.in_(open_exclusion_subq))
         .filter(~Email._id.in_(replies_exclusion_subq))
         .filter(~Email._id.in_(skipped_subq))
         .filter(Email.verified == True)
         .filter(Email._id.in_(last_stage_sent_subq))
         .filter(PreviousStage._id == prev_stage._id)
         .filter(MailMergeSentLog.date_created_utc <= datetime.datetime.utcnow() - datetime.timedelta(days=stage_obj.condition_magnitude) + ff_timedelta)
         )

我认为这个问题加入了这个问题：

.join(CampaignRecipient, and_(CampaignRecipient.email_id == Email._id,
                                   CampaignRecipient.campaign_id == campaign._id))

成为瓶颈。

但是，我有Email._id和CampaignRecipient.email_id的索引，请参阅：

Index('ix_email_id',
      Email._id)

Index('ix_campaign_recipients_email_id',
      CampaignRecipient.email_id)

表的大小为：

# select count(*) from campaign_recipients;
  count
---------
 1155053
(1 row)

和

# select count(*) from email;
 count
--------
 337010
(1 row)

这是原始SQL查询：

explain (analyze, buffers) SELECT email._id AS email__id, email.type AS email_type, email.email AS email_email, email.person_id AS email_person_id, email.organisation_id AS email_organisation_id, email.timestamp_utc AS email_timestamp_utc, email.verified AS email_verified, email.last_verified_timestamp_utc AS email_last_verified_timestamp_utc
    FROM email JOIN campaign_recipients ON campaign_recipients.email_id = email._id AND campaign_recipients.campaign_id = 'ed76aaa4-54d2-11e7-ae1c-0242ac110003'
    WHERE email._id NOT IN (SELECT email._id
    FROM email JOIN mail_merge_sent_log ON mail_merge_sent_log.email_id = email._id
    WHERE mail_merge_sent_log.mail_merge_stage_id = 'ed77797a-54d2-11e7-ae1c-0242ac110003') AND email.verified = true AND email._id NOT IN (SELECT email._id
    FROM email JOIN mail_merge_sent_log ON mail_merge_sent_log.email_id = email._id
    WHERE mail_merge_sent_log.mail_merge_id != mail_merge_sent_log.mail_merge_id) AND email._id NOT IN (SELECT email._id
    FROM email JOIN event_meta ON event_meta.val = email._id JOIN events ON events._id = event_meta.event_id
    WHERE events.campaign_id != events.campaign_id AND events.type = 'open_email' AND event_meta.key = 'email_id') AND email._id NOT IN (SELECT email._id
    FROM email JOIN event_meta ON event_meta.val = email._id JOIN events ON events._id = event_meta.event_id
    WHERE events.campaign_id != events.campaign_id AND events.type = 'new_correspondent' AND event_meta.key = 'email_id') ORDER BY campaign_recipients.order_idx
     LIMIT 1

如何优化此功能？