This may not solve your problem, but it may help. (especially if you use innodb as your storage engine)
I took a look at how the Save method in client.cpp worked and saw some issues in the way locking happens and transactions are used (or not used).
From what I can tell between the lock in front of the DB connection and the lack of bulking up statements into a transaction, this could cause some serious issues if people were not using a very good ssd on their database and had quick network connection to their database of choice. You can easly get 'fsync' choked. Symptions are low io/cpu usage, everything starts lagging out waiting for the locks to be release for fsync to happen on the database for transaction purposes.
I've created a pull request.
https://github.com/EQEmu/Server/pull/827
**WARNING*** my testing has been minimal so use as your own risk, but I am encouraged by the results (over 2x faster with zero load on the system)
**Note**, you will also need to included two indexes on tables, its in the pull request. Its important as we are doing table scans during the save without them.
Hope this can help some of you. right now its a stop gap and hopefully I can come up with a better solution in the near future. I would like feedback if it helps resolve the lag issues with pets out.
This is an example bulking of the transactions of a simple save.
START TRANSACTION;
REPLACE INTO `character_currency` (id, platinum, gold, silver, copper,platinum_bank, gold_bank, silver_bank, copper_bank,platinum_cursor, gold_cursor, silver_cursor, copper_cursor, radiant_crystals, career_radiant_crystals, ebon_crystals, career_ebon_crystals)VALUES (685273, 184, 153, 149, 101, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);
REPLACE INTO `character_bind` (id, zone_id, instance_id, x, y, z, heading, slot) VALUES (685273, 189, 0, 18.000000, -147.000000, 20.000000, 64.000000, 0);
REPLACE INTO `character_bind` (id, zone_id, instance_id, x, y, z, heading, slot) VALUES (685273, 41, 0, -980.000000, 148.000000, -38.000000, 64.000000, 1);
REPLACE INTO `character_bind` (id, zone_id, instance_id, x, y, z, heading, slot) VALUES (685273, 41, 0, -980.000000, 148.000000, -38.000000, 64.000000, 2);
REPLACE INTO `character_bind` (id, zone_id, instance_id, x, y, z, heading, slot) VALUES (685273, 41, 0, -980.000000, 148.000000, -38.000000, 64.000000, 3);
REPLACE INTO `character_bind` (id, zone_id, instance_id, x, y, z, heading, slot) VALUES (685273, 41, 0, -980.000000, 148.000000, -38.000000, 64.000000, 4);
DELETE FROM `character_buffs` WHERE `character_id` = '685273';
DELETE FROM `character_pet_buffs` WHERE `char_id` = 685273;
DELETE FROM `character_pet_inventory` WHERE `char_id` = 685273;
INSERT INTO `character_pet_info` (`char_id`, `pet`, `petname`, `petpower`, `spell_id`, `hp`, `mana`, `size`) VALUES (685273, 0, 'Labann000', 0, 632, 3150, 0, 5.000000) ON DUPLICATE KEY UPDATE `petname` = 'Labann000', `petpower` = 0, `spell_id` = 632, `hp` = 3150, `mana` = 0, `size` = 5.000000;
DELETE FROM `character_tribute` WHERE `id` = 685273;REPLACE INTO character_activities (charid, taskid, activityid, donecount, completed) VALUES (685273, 22, 1, 0, 0), (685273, 22, 2, 0, 0), (685273, 22, 3, 0, 0), (685273, 22, 4, 0, 0), (685273, 22, 5, 0, 0);
REPLACE INTO character_activities (charid, taskid, activityid, donecount, completed) VALUES (685273, 23, 0, 0, 0);REPLACE INTO character_activities (charid, taskid, activityid, donecount, completed) VALUES (685273, 138, 0, 0, 0);
REPLACE INTO `character_data` ( id,account_id,`name`, last_name, gender, race, class, `level`, deity,birthday,last_login,time_played,pvp_status,l evel2, anon, gm, intoxication,hair_color,beard_color,eye_color_1,ey e_color_2,hair_style,beard,ability_time_seconds,ab ility_number,ability_time_minutes,ability_time_hou rs, title,suffix, exp, points, mana, cur_hp, str, sta, cha, dex, `int`,agi, wis, face, y, x, z, heading, pvp2, pvp_type,autosplit_enabled, zone_change_count, drakkin_heritage, drakkin_tattoo,drakkin_details, toxicity,hunger_level,thirst_level,ability_up,zone _id, zone_instance,leadership_exp_on, ldon_points_guk, ldon_points_mir, ldon_points_mmc, ldon_points_ruj, ldon_points_tak, ldon_points_available,tribute_time_remaining, show_helm, career_tribute_points,tribute_points,tribute_activ e,endurance, group_leadership_exp,raid_leadership_exp, group_leadership_points, raid_leadership_points, air_remaining,pvp_kills, pvp_deaths,pvp_current_points, pvp_career_points, pvp_best_kill_streak,pvp_worst_death_streak, pvp_current_kill_streak, aa_points_spent, aa_exp, aa_points, group_auto_consent, raid_auto_consent, guild_auto_consent, RestTimer, e_aa_effects, e_percent_to_aa, e_expended_aa_spent, e_last_invsnapshot, mailkey ) VALUES (685273,90536,'Rekka','',0,6,13,50,396,1550636815, 1552018689,22507,0,70,0,1,0,17,255,4,4,2,255,0,0,0 ,0,'','',164708608,345,2299,1589,60,80,60,75,134,9 0,83,3,-1831.625000,-225.750000,3.127999,37.500000,0,0,0,0,0,0,0,0,4480 ,4480,0,22,0,0,0,0,0,0,0,0,4294967295,0,0,0,0,1291 ,0,0,0,0,60,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,'B F01A8C0586571A2');
COMMIT;
If this doesn't help, I'm sorry if I have muddied the waters a bit.