Estou usando o Postgres 9.3.5 e tenho uma grande tabela no banco de dados, atualmente ela tem mais de 25 milhões de linhas e tende a ficar ainda maior rapidamente. Estou tentando selecionar linhas específicas (todos os unit_ids com apenas o mais recente unit_timestamppara cada uma delas) com uma consulta simples como:
SELECT unit_id, max(unit_timestamp) AS latest_timestamp FROM all_units GROUP BY unit_id;
Sem nenhum índice, essa consulta leva cerca de 35 segundos para ser executada. Com um índice definido ( CREATE INDEX partial_idx ON all_units (unit_id, unit_timestamp DESC);) o tempo de consulta é reduzido para cerca de (apenas) 19 segundos.
Gostaria de saber se será possível executar minha consulta em ainda menos tempo (como apenas alguns segundos) e, em caso afirmativo, quais etapas devo seguir para otimizá-la ainda mais?
Meu dump da estrutura da tabela se parece com isso:
CREATE TABLE "all_units" (
"unit_id" int4 NOT NULL,
"unit_timestamp" timestamp(6) NOT NULL,
"lon" float4,
"lat" float4,
"speed" float4,
"status" varchar(255) COLLATE "default"
)
ALTER TABLE "all_units" ADD PRIMARY KEY ("unit_id", "unit_timestamp");
O EXPLAIN (ANALYZE, BUFFERS)seguinte:
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------
HashAggregate (cost=663998.38..664069.73 rows=7135 width=12) (actual time=84715.050..84732.021 rows=11094 loops=1)
Buffers: shared hit=192 read=286819
-> Seq Scan on ais_sorted (cost=0.00..538335.92 rows=25132492 width=12) (actual time=0.608..41264.196 rows=25132492 loops=1)
Buffers: shared hit=192 read=286819
Total runtime: 84746.501 ms
e minhas configurações de psql no servidor ficam assim:
name | context | min_val | max_val | boot_val
-------------------------------------+------------+-----------+--------------+-----------------------------------------
allow_system_table_mods | postmaster | | | off
application_name | user | | |
archive_command | sighup | | |
archive_mode | postmaster | | | off
archive_timeout | sighup | 0 | 1073741823 | 0
array_nulls | user | | | on
authentication_timeout | sighup | 1 | 600 | 60
autovacuum | sighup | | | on
autovacuum_analyze_scale_factor | sighup | 0 | 100 | 0.1
autovacuum_analyze_threshold | sighup | 0 | 2147483647 | 50
autovacuum_freeze_max_age | postmaster | 100000000 | 2000000000 | 200000000
autovacuum_max_workers | postmaster | 1 | 8388607 | 3
autovacuum_multixact_freeze_max_age | postmaster | 10000000 | 2000000000 | 400000000
autovacuum_naptime | sighup | 1 | 2147483 | 60
autovacuum_vacuum_cost_delay | sighup | -1 | 100 | 20
autovacuum_vacuum_cost_limit | sighup | -1 | 10000 | -1
autovacuum_vacuum_scale_factor | sighup | 0 | 100 | 0.2
autovacuum_vacuum_threshold | sighup | 0 | 2147483647 | 50
backslash_quote | user | | | safe_encoding
bgwriter_delay | sighup | 10 | 10000 | 200
bgwriter_lru_maxpages | sighup | 0 | 1000 | 100
bgwriter_lru_multiplier | sighup | 0 | 10 | 2
block_size | internal | 8192 | 8192 | 8192
bonjour | postmaster | | | off
bonjour_name | postmaster | | |
bytea_output | user | | | hex
check_function_bodies | user | | | on
checkpoint_completion_target | sighup | 0 | 1 | 0.5
checkpoint_segments | sighup | 1 | 2147483647 | 3
checkpoint_timeout | sighup | 30 | 3600 | 300
checkpoint_warning | sighup | 0 | 2147483647 | 30
client_encoding | user | | | SQL_ASCII
client_min_messages | user | | | notice
commit_delay | superuser | 0 | 100000 | 0
commit_siblings | user | 0 | 1000 | 5
config_file | postmaster | | |
constraint_exclusion | user | | | partition
cpu_index_tuple_cost | user | 0 | 1.79769e+308 | 0.005
cpu_operator_cost | user | 0 | 1.79769e+308 | 0.0025
cpu_tuple_cost | user | 0 | 1.79769e+308 | 0.01
cursor_tuple_fraction | user | 0 | 1 | 0.1
data_checksums | internal | | | off
data_directory | postmaster | | |
DateStyle | user | | | ISO, MDY
db_user_namespace | sighup | | | off
deadlock_timeout | superuser | 1 | 2147483647 | 1000
debug_assertions | user | | | off
debug_pretty_print | user | | | on
debug_print_parse | user | | | off
debug_print_plan | user | | | off
debug_print_rewritten | user | | | off
default_statistics_target | user | 1 | 10000 | 100
default_tablespace | user | | |
default_text_search_config | user | | | pg_catalog.simple
default_transaction_deferrable | user | | | off
default_transaction_isolation | user | | | read committed
default_transaction_read_only | user | | | off
default_with_oids | user | | | off
dynamic_library_path | superuser | | | $libdir
effective_cache_size | user | 1 | 2147483647 | 16384
effective_io_concurrency | user | 0 | 1000 | 1
enable_bitmapscan | user | | | on
enable_hashagg | user | | | on
enable_hashjoin | user | | | on
enable_indexonlyscan | user | | | on
enable_indexscan | user | | | on
enable_material | user | | | on
enable_mergejoin | user | | | on
enable_nestloop | user | | | on
enable_seqscan | user | | | on
enable_sort | user | | | on
enable_tidscan | user | | | on
escape_string_warning | user | | | on
event_source | postmaster | | | PostgreSQL
exit_on_error | user | | | off
external_pid_file | postmaster | | |
extra_float_digits | user | -15 | 3 | 0
from_collapse_limit | user | 1 | 2147483647 | 8
fsync | sighup | | | on
full_page_writes | sighup | | | on
geqo | user | | | on
geqo_effort | user | 1 | 10 | 5
geqo_generations | user | 0 | 2147483647 | 0
geqo_pool_size | user | 0 | 2147483647 | 0
geqo_seed | user | 0 | 1 | 0
geqo_selection_bias | user | 1.5 | 2 | 2
geqo_threshold | user | 2 | 2147483647 | 12
gin_fuzzy_search_limit | user | 0 | 2147483647 | 0
hba_file | postmaster | | |
hot_standby | postmaster | | | off
hot_standby_feedback | sighup | | | off
ident_file | postmaster | | |
ignore_checksum_failure | superuser | | | off
ignore_system_indexes | backend | | | off
integer_datetimes | internal | | | on
IntervalStyle | user | | | postgres
join_collapse_limit | user | 1 | 2147483647 | 8
krb_caseins_users | sighup | | | off
krb_server_keyfile | sighup | | | FILE:/etc/postgresql-common/krb5.keytab
krb_srvname | sighup | | | postgres
lc_collate | internal | | | C
lc_ctype | internal | | | C
lc_messages | superuser | | |
lc_monetary | user | | | C
lc_numeric | user | | | C
lc_time | user | | | C
listen_addresses | postmaster | | | localhost
lo_compat_privileges | superuser | | | off
local_preload_libraries | backend | | |
lock_timeout | user | 0 | 2147483647 | 0
log_autovacuum_min_duration | sighup | -1 | 2147483647 | -1
log_checkpoints | sighup | | | off
log_connections | backend | | | off
log_destination | sighup | | | stderr
log_directory | sighup | | | pg_log
log_disconnections | backend | | | off
log_duration | superuser | | | off
log_error_verbosity | superuser | | | default
log_executor_stats | superuser | | | off
log_file_mode | sighup | 0 | 511 | 384
log_filename | sighup | | | postgresql-%Y-%m-%d_%H%M%S.log
log_hostname | sighup | | | off
log_line_prefix | sighup | | |
log_lock_waits | superuser | | | off
log_min_duration_statement | superuser | -1 | 2147483647 | -1
log_min_error_statement | superuser | | | error
log_min_messages | superuser | | | warning
log_parser_stats | superuser | | | off
log_planner_stats | superuser | | | off
log_rotation_age | sighup | 0 | 35791394 | 1440
log_rotation_size | sighup | 0 | 2097151 | 10240
log_statement | superuser | | | none
log_statement_stats | superuser | | | off
log_temp_files | superuser | -1 | 2147483647 | -1
log_timezone | sighup | | | GMT
log_truncate_on_rotation | sighup | | | off
logging_collector | postmaster | | | off
maintenance_work_mem | user | 1024 | 2147483647 | 16384
max_connections | postmaster | 1 | 8388607 | 100
max_files_per_process | postmaster | 25 | 2147483647 | 1000
max_function_args | internal | 100 | 100 | 100
max_identifier_length | internal | 63 | 63 | 63
max_index_keys | internal | 32 | 32 | 32
max_locks_per_transaction | postmaster | 10 | 2147483647 | 64
max_pred_locks_per_transaction | postmaster | 10 | 2147483647 | 64
max_prepared_transactions | postmaster | 0 | 8388607 | 0
max_stack_depth | superuser | 100 | 2147483647 | 100
max_standby_archive_delay | sighup | -1 | 2147483647 | 30000
max_standby_streaming_delay | sighup | -1 | 2147483647 | 30000
max_wal_senders | postmaster | 0 | 8388607 | 0
password_encryption | user | | | on
port | postmaster | 1 | 65535 | 5432
post_auth_delay | backend | 0 | 2147 | 0
pre_auth_delay | sighup | 0 | 60 | 0
quote_all_identifiers | user | | | off
random_page_cost | user | 0 | 1.79769e+308 | 4
restart_after_crash | sighup | | | on
search_path | user | | | "$user",public
segment_size | internal | 131072 | 131072 | 131072
seq_page_cost | user | 0 | 1.79769e+308 | 1
server_encoding | internal | | | SQL_ASCII
server_version | internal | | | 9.3.5
server_version_num | internal | 90305 | 90305 | 90305
session_replication_role | superuser | | | origin
shared_buffers | postmaster | 16 | 1073741823 | 1024
shared_preload_libraries | postmaster | | |
sql_inheritance | user | | | on
ssl | postmaster | | | off
ssl_ca_file | postmaster | | |
ssl_cert_file | postmaster | | | server.crt
ssl_ciphers | postmaster | | | DEFAULT:!LOW:!EXP:!MD5:@STRENGTH
ssl_crl_file | postmaster | | |
ssl_key_file | postmaster | | | server.key
ssl_renegotiation_limit | user | 0 | 2147483647 | 524288
standard_conforming_strings | user | | | on
statement_timeout | user | 0 | 2147483647 | 0
stats_temp_directory | sighup | | | pg_stat_tmp
superuser_reserved_connections | postmaster | 0 | 8388607 | 3
synchronize_seqscans | user | | | on
synchronous_commit | user | | | on
synchronous_standby_names | sighup | | |
syslog_facility | sighup | | | local0
syslog_ident | sighup | | | postgres
tcp_keepalives_count | user | 0 | 2147483647 | 0
tcp_keepalives_idle | user | 0 | 2147483647 | 0
tcp_keepalives_interval | user | 0 | 2147483647 | 0
temp_buffers | user | 100 | 1073741823 | 1024
temp_file_limit | superuser | -1 | 2147483647 | -1
temp_tablespaces | user | | |
TimeZone | user | | | GMT
timezone_abbreviations | user | | |
trace_notify | user | | | off
trace_recovery_messages | sighup | | | log
trace_sort | user | | | off
track_activities | superuser | | | on
track_activity_query_size | postmaster | 100 | 102400 | 1024
track_counts | superuser | | | on
track_functions | superuser | | | none
track_io_timing | superuser | | | off
transaction_deferrable | user | | | off
transaction_isolation | user | | | default
transaction_read_only | user | | | off
transform_null_equals | user | | | off
unix_socket_directories | postmaster | | | /var/run/postgresql
unix_socket_group | postmaster | | |
unix_socket_permissions | postmaster | 0 | 511 | 511
update_process_title | superuser | | | on
vacuum_cost_delay | user | 0 | 100 | 0
vacuum_cost_limit | user | 1 | 10000 | 200
vacuum_cost_page_dirty | user | 0 | 10000 | 20
vacuum_cost_page_hit | user | 0 | 10000 | 1
vacuum_cost_page_miss | user | 0 | 10000 | 10
vacuum_defer_cleanup_age | sighup | 0 | 1000000 | 0
vacuum_freeze_min_age | user | 0 | 1000000000 | 50000000
vacuum_freeze_table_age | user | 0 | 2000000000 | 150000000
vacuum_multixact_freeze_min_age | user | 0 | 1000000000 | 5000000
vacuum_multixact_freeze_table_age | user | 0 | 2000000000 | 150000000
wal_block_size | internal | 8192 | 8192 | 8192
wal_buffers | postmaster | -1 | 2147483647 | -1
wal_keep_segments | sighup | 0 | 2147483647 | 0
wal_level | postmaster | | | minimal
wal_receiver_status_interval | sighup | 0 | 2147483 | 10
wal_receiver_timeout | sighup | 0 | 2147483647 | 60000
wal_segment_size | internal | 2048 | 2048 | 2048
wal_sender_timeout | sighup | 0 | 2147483647 | 60000
wal_sync_method | sighup | | | fdatasync
wal_writer_delay | sighup | 1 | 10000 | 200
work_mem | user | 64 | 2147483647 | 1024
xmlbinary | user | | | base64
xmloption | user | | | content
zero_damaged_pages | superuser | | | off
