Nominatim slow query

I recently imported the nominatim with full planet and queries are undesirable performance. The first query, before the cache is created, takes longer than 20 seconds and sometimes I see this error:

Internal Server Error
Nominatim has encountered an internal error while accessing the database. This may happen because the database is broken or because of a bug in the software. If you think it is a bug, feel free to report it over on Github. Please include the URL that caused the problem and the complete error details below.
Message: Could not lookup place
SQL Error: DB Error: unknown error
Details:
SELECT     osm_type,    osm_id,    class,    type,    admin_level,    rank_search,    rank_address,    min(place_id) AS place_id,    min(parent_place_id) AS parent_place_id,    -1 as housenumber,    country_code,get_address_by_language(place_id,-1,ARRAY['short_name','name','brand','official_name','ref','type']) AS langaddress,    get_name_by_language(name,ARRAY['short_name','name','brand','official_name','ref','type']) AS placename,    get_name_by_language(name, ARRAY['ref']) AS ref,    avg(ST_X(centroid)) AS lon,     avg(ST_Y(centroid)) AS lat,     COALESCE(importance,0.75-(rank_search::float/40)) AS importance, (SELECT max(ai_p.importance * (ai_p.rank_address + 2))   FROM place_addressline ai_s, placex ai_p   WHERE ai_s.place_id = min(CASE WHEN placex.rank_search < 28 THEN placex.place_id ELSE placex.parent_place_id END)     AND ai_p.place_id = ai_s.address_place_id      AND ai_s.isaddress      AND ai_p.importance is not null) AS addressimportance,    (extratags->'place') AS extra_place  FROM placex WHERE place_id in (92672355,196842012,4488269,196732908,48310082,160137,91687842,70711723,83690356,77366185,74053027,92460750,82583385,113120861,177719652,86034442,82755806,76866792,83301006,92789547)    AND (        placex.rank_address between 0 and 30     OR (extratags->'place') = 'city'       )     AND linked_place_id is null  GROUP BY      osm_type,      osm_id,      class,      type,      admin_level,      rank_search,      rank_address,      housenumber,     country_code,      importance,      langaddress,      placename,      ref,      extratags->'place'  [nativecode=ERROR:  canceling statement due to statement timeout
CONTEXT:  PL/pgSQL function get_addressdata(bigint,integer) line 103 at FOR over SELECT rows
PL/pgSQL function get_address_by_language(bigint,integer,text[]) line 12 at FOR over SELECT rows]

Due to the delay of the queries I thought the problem was the lack of some index and then I executed:

nohup ./utils/setup.php --create-search-indices --ignore-errors &

Output:

2018-08-13 20:59:56 == Create Search indices
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LANGUAGE = (unset),
    LC_ALL = (unset),
    LC_CTYPE = "UTF-8",
    LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_US.UTF-8").
ERROR:  relation "idx_word_word_id" already exists
ERROR:  relation "idx_search_name_nameaddress_vector" already exists
ERROR:  relation "idx_search_name_name_vector" already exists
ERROR:  relation "idx_search_name_centroid" already exists
ERROR:  relation "idx_place_addressline_address_place_id" already exists
ERROR:  relation "idx_placex_rank_address" already exists
ERROR:  relation "idx_placex_pendingsector" already exists
ERROR:  relation "idx_placex_parent_place_id" already exists
ERROR:  relation "idx_placex_reverse_geometry" already exists
ERROR:  relation "idx_location_area_country_place_id" already exists
ERROR:  relation "idx_osmline_parent_place_id" already exists
ERROR:  relation "idx_search_name_country_centroid" already exists
NOTICE:  index "place_id_idx" does not exist, skipping
ERROR:  relation "idx_place_osm_unique" already exists
ERROR:  relation "idx_postcode_id" already exists
ERROR:  relation "idx_postcode_postcode" already exists
Summary of warnings:


2018-08-14 02:23:14 == Setup finished.

What does this line mean? NOTICE: index "place_id_idx" does not exist, skipping

After that, I turn on the postgresql log and called the search api with these parameters:

http://nominatim.dev/nominatim/search.php?format=jsonv2&addressdetails=1&q=cancun

Logs:

2018-08-14 14:30:49 UTC [2489-1] www-data@nominatim LOG:  duration: 16092.775 ms  statement: SELECT     osm_type,    osm_id,    class,    type,    admin_level,    rank_search,    rank_address,    min(place_id) AS place_id,    min(parent_place_id) AS parent_place_id,    -1 as housenumber,    country_code,get_address_by_language(place_id,-1,ARRAY['short_name:en-en','name:en-en','short_name:en','name:en','short_name','name','brand','official_name:en-en','official_name:en','official_name','ref','type']) AS langaddress,    get_name_by_language(name,ARRAY['short_name:en-en','name:en-en','short_name:en','name:en','short_name','name','brand','official_name:en-en','official_name:en','official_name','ref','type']) AS placename,    get_name_by_language(name, ARRAY['ref']) AS ref,    avg(ST_X(centroid)) AS lon,     avg(ST_Y(centroid)) AS lat,     COALESCE(importance,0.75-(rank_search::float/40)) AS importance, (SELECT max(ai_p.importance * (ai_p.rank_address + 2))   FROM place_addressline ai_s, placex ai_p   WHERE ai_s.place_id = min(CASE WHEN placex.rank_search < 28 THEN placex.place_id ELSE placex.parent_place_id END)     AND ai_p.place_id = ai_s.address_place_id      AND ai_s.isaddress      AND ai_p.importance is not null) AS addressimportance,    (extratags->'place') AS extra_place  FROM placex WHERE place_id in (197441826,111603036,182595459,139694930,144830394,118512715,74049435,99932703,159450111,141912308,112119380,80303695,80305679,112647794,80522782,115827503,128389572,149585949,74675442,150225528)    AND (        placex.rank_address between 0 and 30     OR (extratags->'place') = 'city'       )     AND linked_place_id is null  GROUP BY      osm_type,      osm_id,      class,      type,      admin_level,      rank_search,      rank_address,      housenumber,     country_code,      importance,      langaddress,      placename,      ref,      extratags->'place'

2018-08-14 14:31:35 UTC [2490-1] ERROR:  function transliteration(text) does not exist at character 23
2018-08-14 14:31:35 UTC [2490-2] HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
2018-08-14 14:31:35 UTC [2490-3] QUERY:  SELECT gettokenstring(transliteration(name))
2018-08-14 14:31:35 UTC [2490-4] CONTEXT:  PL/pgSQL function public.make_standard_name(text) line 5 at assignment
    automatic analyze of table "nominatim.public.placex"

Looking at the logs I thought some functions might be missing, and execute this:

nohup ./utils/setup.php --create-functions --ignore-errors &

2018-08-14 14:48:04 == Create Functions
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
    LANGUAGE = (unset),
    LC_ALL = (unset),
    LC_CTYPE = "UTF-8",
    LANG = "en_US.UTF-8"
    are supported and installed on your system.
perl: warning: Falling back to a fallback locale ("en_US.UTF-8").
NOTICE:  drop cascades to function get_addressdata(bigint,integer)
NOTICE:  drop cascades to function get_wikipedia_match(hstore,character varying)
Summary of warnings:


2018-08-14 14:48:04 == Setup finished.

Some info about my installation:

Nominatim version 3.1.0

Ec2 t2.2xlarge with T2 Unlimited | vCPU 8 | 32GB RAM | SSD 870 GB gp2 2610/3000 IOPS

 Postgresql configurations:
- shared_buffers = 2GB
- maintenance_work_mem = 10GB
- work_mem = 50MB
- effective_cache_size = 24GB
- synchronous_commit = off
- checkpoint_timeout = 10min
- checkpoint_completion_target = 0.9
- fsync = on
- full_page_writes = on
- random_page_cost = 1.1
- wal_buffers = 16MB
- max_worker_processes = 8

df -h

Filesystem      Size  Used Avail Use% Mounted on
udev             16G     0   16G   0% /dev
tmpfs           3.2G  9.5M  3.2G   1% /run
/dev/xvda1      844G  674G  170G  80% /
tmpfs            16G  4.0K   16G   1% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs            16G     0   16G   0% /sys/fs/cgroup
/dev/loop0       13M   13M     0 100% /snap/amazon-ssm-agent/295
/dev/loop1       87M   87M     0 100% /snap/core/4917
/dev/loop2       87M   87M     0 100% /snap/core/4830
/dev/loop3       87M   87M     0 100% /snap/core/5145
tmpfs           3.2G     0  3.2G   0% /run/user/1000

free -h 

              total        used        free      shared  buff/cache   available
Mem:            31G        171M         29G        115M        1.5G         30G
Swap:            0B          0B          0B

nominatim=# \d search_name
                Table "public.search_name"
       Column       |          Type           | Modifiers
--------------------+-------------------------+-----------
 place_id           | bigint                  |
 importance         | double precision        |
 search_rank        | smallint                |
 address_rank       | smallint                |
 name_vector        | integer[]               |
 nameaddress_vector | integer[]               |
 country_code       | character varying(2)    |
 centroid           | geometry(Geometry,4326) |
Indexes:
    "idx_search_name_centroid" gist (centroid)
    "idx_search_name_name_vector" gin (name_vector) WITH (fastupdate=off)
    "idx_search_name_nameaddress_vector" gin (nameaddress_vector) WITH (fastupdate=off)
    "idx_search_name_place_id" btree (place_id)

nominatim=# \d placex
                   Table "public.placex"
     Column      |            Type             | Modifiers
-----------------+-----------------------------+-----------
 place_id        | bigint                      | not null
 parent_place_id | bigint                      |
 linked_place_id | bigint                      |
 importance      | double precision            |
 indexed_date    | timestamp without time zone |
 geometry_sector | integer                     |
 rank_address    | smallint                    |
 rank_search     | smallint                    |
 partition       | smallint                    |
 indexed_status  | smallint                    |
 osm_id          | bigint                      | not null
 osm_type        | character(1)                | not null
 class           | text                        | not null
 type            | text                        | not null
 name            | hstore                      |
 admin_level     | smallint                    |
 address         | hstore                      |
 extratags       | hstore                      |
 geometry        | geometry(Geometry,4326)     | not null
 wikipedia       | text                        |
 country_code    | character varying(2)        |
 housenumber     | text                        |
 postcode        | text                        |
 centroid        | geometry(Geometry,4326)     |
Indexes:
    "idx_place_id" UNIQUE, btree (place_id)
    "idx_placex_adminname" btree (make_standard_name(name -> 'name'::text), rank_search) WHERE osm_type = 'N'::bpchar AND rank_search < 26
    "idx_placex_geometry" gist (geometry)
    "idx_placex_linked_place_id" btree (linked_place_id) WHERE linked_place_id IS NOT NULL
    "idx_placex_osmid" btree (osm_type, osm_id)
    "idx_placex_parent_place_id" btree (parent_place_id) WHERE parent_place_id IS NOT NULL
    "idx_placex_pendingsector" btree (rank_search, geometry_sector) WHERE indexed_status > 0
    "idx_placex_rank_address" btree (rank_address)
    "idx_placex_rank_search" btree (rank_search)
    "idx_placex_reverse_geometry" gist (geometry) WHERE rank_search <> 28 AND (name IS NOT NULL OR housenumber IS NOT NULL) AND (class <> ALL (ARRAY['waterway'::text, 'railway'::text, 'tunnel'::text, 'bridge'::text, 'man_made'::text]))
Triggers:
    placex_before_delete AFTER DELETE ON placex FOR EACH ROW EXECUTE PROCEDURE placex_delete()
    placex_before_insert BEFORE INSERT ON placex FOR EACH ROW EXECUTE PROCEDURE placex_insert()
    placex_before_update BEFORE UPDATE ON placex FOR EACH ROW EXECUTE PROCEDURE placex_update()

I did not come up with a solution with no command executed

What else can I do to try to solve this?