Hi all,
I'm migrating a web application to an ORM framework (Doctrine) so I need a new way to get statistics about entities into the application without importing all data, only the results (e.g. load total number of children instead of loading all children into the application and counting it afterwards). My current solution is to create a view for those statistics and map it to an (read-only) entity in my application. This view is joined with the table containing the entities on which I need statistics.
The entity table is called 'work'. The view containing statistical information about works is called wps2.
The problem is that this join is performing very badly when more than one work is involved. It chooses a plan that is orders of magnitude slower.
I have attached
- The (simplified) table definitions
- The (simplified) view
- Two queries with explain analyze plan: "IN (1)" => fast, "IN (1,3)" => slow
- postgresql.conf
I do not understand why the planner does not consider the nested loop in the second case, like it does in the first case.
Can anyone help me?
Thanks.
Kind regards,
Mathieu
TABLE work (50k rows)
==========
Table "public.work"
Column | Type | Modifiers
----------------------+--------------------------+---------------------------------------------------
id | integer | not null default nextval('work_id_seq'::regclass)
Indexes:
"work_pkey" PRIMARY KEY, btree (id)
Referenced by:
TABLE "adaptation" CONSTRAINT "adaptation_adapted_id_fkey" FOREIGN KEY (adapted_id) REFERENCES work(id) ON DELETE CASCADE
TABLE "adaptation" CONSTRAINT "adaptation_original_id_fkey" FOREIGN KEY (original_id) REFERENCES work(id)
TABLE adaptation (10k rows)
================
Table "public.adaptation"
Column | Type | Modifiers
---------------+--------------------------+---------------------------------------------------------
id | integer | not null default nextval('adaptation_id_seq'::regclass)
original_id | integer | not null
adapted_id | integer | not null
Indexes:
"adaptation_pkey" PRIMARY KEY, btree (id)
"adaptation_adapted_idx" btree (adapted_id)
"adaptation_original_idx" btree (original_id)
Check constraints:
"self_adapt" CHECK (original_id <> adapted_id)
Foreign-key constraints:
"adaptation_adapted_id_fkey" FOREIGN KEY (adapted_id) REFERENCES work(id) ON DELETE CASCADE
"adaptation_original_id_fkey" FOREIGN KEY (original_id) REFERENCES work(id)
VIEW wps2
=========
View "public.wps2"
Column | Type | Modifiers | Storage | Description
--------+---------+-----------+---------+-------------
id | integer | | plain |
count | bigint | | plain |
View definition:
SELECT w.id, count(*) AS count
FROM work w
JOIN ( SELECT w.id, w.id AS ref
FROM work w
UNION ALL
SELECT d.adapted_id AS id, d.original_id AS ref
FROM adaptation d) x ON w.id = x.ref
GROUP BY w.id;
Query 1 : IN with one element
=============================
shs-local=# explain analyze SELECT w.id, wps.* FROM work w LEFT JOIN wps2 wps ON w.id = wps.id WHERE w.id in (1);
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------
Nested Loop Left Join (cost=0.00..33.17 rows=1 width=16) (actual time=0.062..0.064 rows=1 loops=1)
Join Filter: (w.id = w.id)
-> Index Scan using work_pkey on work w (cost=0.00..8.28 rows=1 width=4) (actual time=0.021..0.022 rows=1 loops=1)
Index Cond: (id = 1)
-> GroupAggregate (cost=0.00..24.87 rows=1 width=4) (actual time=0.032..0.032 rows=1 loops=1)
-> Nested Loop (cost=0.00..24.85 rows=2 width=4) (actual time=0.010..0.027 rows=4 loops=1)
-> Index Scan using work_pkey on work w (cost=0.00..8.28 rows=1 width=4) (actual time=0.004..0.005 rows=1 loops=1)
Index Cond: (id = 1)
-> Append (cost=0.00..16.55 rows=2 width=4) (actual time=0.005..0.018 rows=4 loops=1)
-> Index Scan using work_pkey on work w (cost=0.00..8.28 rows=1 width=4) (actual time=0.005..0.006 rows=1 loops=1)
Index Cond: (id = 1)
-> Index Scan using adaptation_original_idx on adaptation d (cost=0.00..8.27 rows=1 width=4) (actual time=0.006..0.011 rows=3 loops=1)
Index Cond: (original_id = 1)
Total runtime: 0.181 ms
Query 2 : IN with two elements
==============================
shs-local=# explain analyze SELECT w.id, wps.* FROM work w LEFT JOIN wps2 wps ON w.id = wps.id WHERE w.id in (1, 3);
QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------------------------
Merge Right Join (cost=14434.97..16024.43 rows=2 width=16) (actual time=101.258..101.261 rows=2 loops=1)
Merge Cond: (w.id = w.id)
-> GroupAggregate (cost=14418.57..15378.25 rows=50381 width=4) (actual time=101.215..101.217 rows=3 loops=1)
-> Sort (cost=14418.57..14570.53 rows=60782 width=4) (actual time=101.208..101.209 rows=9 loops=1)
Sort Key: w.id
Sort Method: external merge Disk: 824kB
-> Hash Join (cost=3751.57..8756.03 rows=60782 width=4) (actual time=24.223..69.882 rows=60783 loops=1)
Hash Cond: (w.id = w.id)
-> Append (cost=0.00..3115.82 rows=60782 width=4) (actual time=0.051..14.467 rows=60783 loops=1)
-> Seq Scan on work w (cost=0.00..2924.81 rows=50381 width=4) (actual time=0.050..9.206 rows=50382 loops=1)
-> Seq Scan on adaptation d (cost=0.00..191.01 rows=10401 width=4) (actual time=0.002..1.805 rows=10401 loops=1)
-> Hash (cost=2924.81..2924.81 rows=50381 width=4) (actual time=24.109..24.109 rows=50382 loops=1)
Buckets: 4096 Batches: 2 Memory Usage: 887kB
-> Seq Scan on work w (cost=0.00..2924.81 rows=50381 width=4) (actual time=0.005..12.655 rows=50382 loops=1)
-> Sort (cost=16.39..16.40 rows=2 width=4) (actual time=0.039..0.040 rows=2 loops=1)
Sort Key: w.id
Sort Method: quicksort Memory: 25kB
-> Bitmap Heap Scan on work w (cost=8.53..16.38 rows=2 width=4) (actual time=0.028..0.029 rows=2 loops=1)
Recheck Cond: (id = ANY ('{1,3}'::integer[]))
-> Bitmap Index Scan on work_pkey (cost=0.00..8.53 rows=2 width=0) (actual time=0.022..0.022 rows=2 loops=1)
Index Cond: (id = ANY ('{1,3}'::integer[]))
Total runtime: 101.560 ms
POSTGRESQL.CONF
===============
# -----------------------------
# PostgreSQL configuration file
# -----------------------------
#
# This file consists of lines of the form:
#
# name = value
#
# (The "=" is optional.) Whitespace may be used. Comments are introduced with
# "#" anywhere on a line. The complete list of parameter names and allowed
# values can be found in the PostgreSQL documentation.
#
# The commented-out settings shown in this file represent the default values.
# Re-commenting a setting is NOT sufficient to revert it to the default value;
# you need to reload the server.
#
# This file is read on server startup and when the server receives a SIGHUP
# signal. If you edit the file on a running system, you have to SIGHUP the
# server for the changes to take effect, or use "pg_ctl reload". Some
# parameters, which are marked below, require a server shutdown and restart to
# take effect.
#
# Any parameter can also be given as a command-line option to the server, e.g.,
# "postgres -c log_connections=on". Some parameters can be changed at run time
# with the "SET" SQL command.
#
# Memory units: kB = kilobytes Time units: ms = milliseconds
# MB = megabytes s = seconds
# GB = gigabytes min = minutes
# h = hours
# d = days
#------------------------------------------------------------------------------
# FILE LOCATIONS
#------------------------------------------------------------------------------
# The default values of these variables are driven from the -D command-line
# option or PGDATA environment variable, represented here as ConfigDir.
data_directory = '/var/lib/postgresql/9.1/main' # use data in another directory
# (change requires restart)
hba_file = '/etc/postgresql/9.1/main/pg_hba.conf' # host-based authentication file
# (change requires restart)
ident_file = '/etc/postgresql/9.1/main/pg_ident.conf' # ident configuration file
# (change requires restart)
# If external_pid_file is not explicitly set, no extra PID file is written.
external_pid_file = '/var/run/postgresql/9.1-main.pid' # write an extra PID file
# (change requires restart)
#------------------------------------------------------------------------------
# CONNECTIONS AND AUTHENTICATION
#------------------------------------------------------------------------------
# - Connection Settings -
#listen_addresses = 'localhost' # what IP address(es) to listen on;
# comma-separated list of addresses;
# defaults to 'localhost', '*' = all
# (change requires restart)
port = 5432 # (change requires restart)
max_connections = 100 # (change requires restart)
# Note: Increasing max_connections costs ~400 bytes of shared memory per
# connection slot, plus lock space (see max_locks_per_transaction).
#superuser_reserved_connections = 3 # (change requires restart)
unix_socket_directory = '/var/run/postgresql' # (change requires restart)
#unix_socket_group = '' # (change requires restart)
#unix_socket_permissions = 0777 # begin with 0 to use octal notation
# (change requires restart)
#bonjour = off # advertise server via Bonjour
# (change requires restart)
#bonjour_name = '' # defaults to the computer name
# (change requires restart)
# - Security and Authentication -
#authentication_timeout = 1min # 1s-600s
ssl = true # (change requires restart)
#ssl_ciphers = 'ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH' # allowed SSL ciphers
# (change requires restart)
#ssl_renegotiation_limit = 512MB # amount of data between renegotiations
#password_encryption = on
#db_user_namespace = off
# Kerberos and GSSAPI
#krb_server_keyfile = ''
#krb_srvname = 'postgres' # (Kerberos only)
#krb_caseins_users = off
# - TCP Keepalives -
# see "man 7 tcp" for details
#tcp_keepalives_idle = 0 # TCP_KEEPIDLE, in seconds;
# 0 selects the system default
#tcp_keepalives_interval = 0 # TCP_KEEPINTVL, in seconds;
# 0 selects the system default
#tcp_keepalives_count = 0 # TCP_KEEPCNT;
# 0 selects the system default
#------------------------------------------------------------------------------
# RESOURCE USAGE (except WAL)
#------------------------------------------------------------------------------
# - Memory -
shared_buffers = 24MB # min 128kB
# (change requires restart)
#temp_buffers = 8MB # min 800kB
#max_prepared_transactions = 0 # zero disables the feature
# (change requires restart)
# Note: Increasing max_prepared_transactions costs ~600 bytes of shared memory
# per transaction slot, plus lock space (see max_locks_per_transaction).
# It is not advisable to set max_prepared_transactions nonzero unless you
# actively intend to use prepared transactions.
#work_mem = 1MB # min 64kB
#maintenance_work_mem = 16MB # min 1MB
#max_stack_depth = 2MB # min 100kB
# - Kernel Resource Usage -
#max_files_per_process = 1000 # min 25
# (change requires restart)
#shared_preload_libraries = '' # (change requires restart)
# - Cost-Based Vacuum Delay -
#vacuum_cost_delay = 0ms # 0-100 milliseconds
#vacuum_cost_page_hit = 1 # 0-10000 credits
#vacuum_cost_page_miss = 10 # 0-10000 credits
#vacuum_cost_page_dirty = 20 # 0-10000 credits
#vacuum_cost_limit = 200 # 1-10000 credits
# - Background Writer -
#bgwriter_delay = 200ms # 10-10000ms between rounds
#bgwriter_lru_maxpages = 100 # 0-1000 max buffers written/round
#bgwriter_lru_multiplier = 2.0 # 0-10.0 multipler on buffers scanned/round
# - Asynchronous Behavior -
#effective_io_concurrency = 1 # 1-1000. 0 disables prefetching
#------------------------------------------------------------------------------
# WRITE AHEAD LOG
#------------------------------------------------------------------------------
# - Settings -
#wal_level = minimal # minimal, archive, or hot_standby
# (change requires restart)
#fsync = on # turns forced synchronization on or off
#synchronous_commit = on # synchronization level; on, off, or local
#wal_sync_method = fsync # the default is the first option
# supported by the operating system:
# open_datasync
# fdatasync (default on Linux)
# fsync
# fsync_writethrough
# open_sync
#full_page_writes = on # recover from partial page writes
#wal_buffers = -1 # min 32kB, -1 sets based on shared_buffers
# (change requires restart)
#wal_writer_delay = 200ms # 1-10000 milliseconds
#commit_delay = 0 # range 0-100000, in microseconds
#commit_siblings = 5 # range 1-1000
# - Checkpoints -
#checkpoint_segments = 3 # in logfile segments, min 1, 16MB each
#checkpoint_timeout = 5min # range 30s-1h
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s # 0 disables
# - Archiving -
#archive_mode = off # allows archiving to be done
# (change requires restart)
#archive_command = '' # command to use to archive a logfile segment
#archive_timeout = 0 # force a logfile segment switch after this
# number of seconds; 0 disables
#------------------------------------------------------------------------------
# REPLICATION
#------------------------------------------------------------------------------
# - Master Server -
# These settings are ignored on a standby server
#max_wal_senders = 0 # max number of walsender processes
# (change requires restart)
#wal_sender_delay = 1s # walsender cycle time, 1-10000 milliseconds
#wal_keep_segments = 0 # in logfile segments, 16MB each; 0 disables
#vacuum_defer_cleanup_age = 0 # number of xacts by which cleanup is delayed
#replication_timeout = 60s # in milliseconds; 0 disables
#synchronous_standby_names = '' # standby servers that provide sync rep
# comma-separated list of application_name
# from standby(s); '*' = all
# - Standby Servers -
# These settings are ignored on a master server
#hot_standby = off # "on" allows queries during recovery
# (change requires restart)
#max_standby_archive_delay = 30s # max delay before canceling queries
# when reading WAL from archive;
# -1 allows indefinite delay
#max_standby_streaming_delay = 30s # max delay before canceling queries
# when reading streaming WAL;
# -1 allows indefinite delay
#wal_receiver_status_interval = 10s # send replies at least this often
# 0 disables
#hot_standby_feedback = off # send info from standby to prevent
# query conflicts
#------------------------------------------------------------------------------
# QUERY TUNING
#------------------------------------------------------------------------------
# - Planner Method Configuration -
#enable_bitmapscan = on
#enable_hashagg = on
#enable_hashjoin = on
#enable_indexscan = on
#enable_material = on
#enable_mergejoin = on
#enable_nestloop = on
#enable_seqscan = on
#enable_sort = on
#enable_tidscan = on
# - Planner Cost Constants -
#seq_page_cost = 1.0 # measured on an arbitrary scale
#random_page_cost = 4.0 # same scale as above
#cpu_tuple_cost = 0.01 # same scale as above
#cpu_index_tuple_cost = 0.005 # same scale as above
#cpu_operator_cost = 0.0025 # same scale as above
#effective_cache_size = 128MB
# - Genetic Query Optimizer -
#geqo = on
#geqo_threshold = 12
#geqo_effort = 5 # range 1-10
#geqo_pool_size = 0 # selects default based on effort
#geqo_generations = 0 # selects default based on effort
#geqo_selection_bias = 2.0 # range 1.5-2.0
#geqo_seed = 0.0 # range 0.0-1.0
# - Other Planner Options -
#default_statistics_target = 100 # range 1-10000
#constraint_exclusion = partition # on, off, or partition
#cursor_tuple_fraction = 0.1 # range 0.0-1.0
#from_collapse_limit = 8
#join_collapse_limit = 8 # 1 disables collapsing of explicit
# JOIN clauses
#------------------------------------------------------------------------------
# ERROR REPORTING AND LOGGING
#------------------------------------------------------------------------------
# - Where to Log -
#log_destination = 'stderr' # Valid values are combinations of
# stderr, csvlog, syslog, and eventlog,
# depending on platform. csvlog
# requires logging_collector to be on.
# This is used when logging to stderr:
#logging_collector = off # Enable capturing of stderr and csvlog
# into log files. Required to be on for
# csvlogs.
# (change requires restart)
# These are only used if logging_collector is on:
#log_directory = 'pg_log' # directory where log files are written,
# can be absolute or relative to PGDATA
#log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log' # log file name pattern,
# can include strftime() escapes
#log_file_mode = 0600 # creation mode for log files,
# begin with 0 to use octal notation
#log_truncate_on_rotation = off # If on, an existing log file with the
# same name as the new log file will be
# truncated rather than appended to.
# But such truncation only occurs on
# time-driven rotation, not on restarts
# or size-driven rotation. Default is
# off, meaning append to existing files
# in all cases.
#log_rotation_age = 1d # Automatic rotation of logfiles will
# happen after that time. 0 disables.
#log_rotation_size = 10MB # Automatic rotation of logfiles will
# happen after that much log output.
# 0 disables.
# These are relevant when logging to syslog:
#syslog_facility = 'LOCAL0'
#syslog_ident = 'postgres'
#silent_mode = off # Run server silently.
# DO NOT USE without syslog or
# logging_collector
# (change requires restart)
# - When to Log -
#client_min_messages = notice # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# log
# notice
# warning
# error
#log_min_messages = warning # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# info
# notice
# warning
# error
# log
# fatal
# panic
#log_min_error_statement = error # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# info
# notice
# warning
# error
# log
# fatal
# panic (effectively off)
#log_min_duration_statement = -1 # -1 is disabled, 0 logs all statements
# and their durations, > 0 logs only
# statements running at least this number
# of milliseconds
# - What to Log -
#debug_print_parse = off
#debug_print_rewritten = off
#debug_print_plan = off
#debug_pretty_print = on
#log_checkpoints = off
#log_connections = off
#log_disconnections = off
#log_duration = off
#log_error_verbosity = default # terse, default, or verbose messages
#log_hostname = off
log_line_prefix = '%t ' # special values:
# %a = application name
# %u = user name
# %d = database name
# %r = remote host and port
# %h = remote host
# %p = process ID
# %t = timestamp without milliseconds
# %m = timestamp with milliseconds
# %i = command tag
# %e = SQL state
# %c = session ID
# %l = session line number
# %s = session start timestamp
# %v = virtual transaction ID
# %x = transaction ID (0 if none)
# %q = stop here in non-session
# processes
# %% = '%'
# e.g. '<%u%%%d> '
#log_lock_waits = off # log lock waits >= deadlock_timeout
#log_statement = 'none' # none, ddl, mod, all
#log_temp_files = -1 # log temporary files equal or larger
# than the specified size in kilobytes;
# -1 disables, 0 logs all temp files
#log_timezone = '(defaults to server environment setting)'
#------------------------------------------------------------------------------
# RUNTIME STATISTICS
#------------------------------------------------------------------------------
# - Query/Index Statistics Collector -
#track_activities = on
#track_counts = on
#track_functions = none # none, pl, all
#track_activity_query_size = 1024 # (change requires restart)
#update_process_title = on
#stats_temp_directory = 'pg_stat_tmp'
# - Statistics Monitoring -
#log_parser_stats = off
#log_planner_stats = off
#log_executor_stats = off
#log_statement_stats = off
#------------------------------------------------------------------------------
# AUTOVACUUM PARAMETERS
#------------------------------------------------------------------------------
#autovacuum = on # Enable autovacuum subprocess? 'on'
# requires track_counts to also be on.
#log_autovacuum_min_duration = -1 # -1 disables, 0 logs all actions and
# their durations, > 0 logs only
# actions running at least this number
# of milliseconds.
#autovacuum_max_workers = 3 # max number of autovacuum subprocesses
# (change requires restart)
#autovacuum_naptime = 1min # time between autovacuum runs
#autovacuum_vacuum_threshold = 50 # min number of row updates before
# vacuum
#autovacuum_analyze_threshold = 50 # min number of row updates before
# analyze
#autovacuum_vacuum_scale_factor = 0.2 # fraction of table size before vacuum
#autovacuum_analyze_scale_factor = 0.1 # fraction of table size before analyze
#autovacuum_freeze_max_age = 200000000 # maximum XID age before forced vacuum
# (change requires restart)
#autovacuum_vacuum_cost_delay = 20ms # default vacuum cost delay for
# autovacuum, in milliseconds;
# -1 means use vacuum_cost_delay
#autovacuum_vacuum_cost_limit = -1 # default vacuum cost limit for
# autovacuum, -1 means use
# vacuum_cost_limit
#------------------------------------------------------------------------------
# CLIENT CONNECTION DEFAULTS
#------------------------------------------------------------------------------
# - Statement Behavior -
#search_path = '"$user",public' # schema names
#default_tablespace = '' # a tablespace name, '' uses the default
#temp_tablespaces = '' # a list of tablespace names, '' uses
# only default tablespace
#check_function_bodies = on
#default_transaction_isolation = 'read committed'
#default_transaction_read_only = off
#default_transaction_deferrable = off
#session_replication_role = 'origin'
#statement_timeout = 0 # in milliseconds, 0 is disabled
#vacuum_freeze_min_age = 50000000
#vacuum_freeze_table_age = 150000000
#bytea_output = 'hex' # hex, escape
#xmlbinary = 'base64'
#xmloption = 'content'
# - Locale and Formatting -
datestyle = 'iso, dmy'
#intervalstyle = 'postgres'
#timezone = '(defaults to server environment setting)'
#timezone_abbreviations = 'Default' # Select the set of available time zone
# abbreviations. Currently, there are
# Default
# Australia
# India
# You can create your own file in
# share/timezonesets/.
#extra_float_digits = 0 # min -15, max 3
#client_encoding = sql_ascii # actually, defaults to database
# encoding
# These settings are initialized by initdb, but they can be changed.
lc_messages = 'en_US.UTF-8' # locale for system error message
# strings
lc_monetary = 'nl_BE.UTF-8' # locale for monetary formatting
lc_numeric = 'nl_BE.UTF-8' # locale for number formatting
lc_time = 'nl_BE.UTF-8' # locale for time formatting
# default configuration for text search
default_text_search_config = 'pg_catalog.english'
# - Other Defaults -
#dynamic_library_path = '$libdir'
#local_preload_libraries = ''
#------------------------------------------------------------------------------
# LOCK MANAGEMENT
#------------------------------------------------------------------------------
#deadlock_timeout = 1s
#max_locks_per_transaction = 64 # min 10
# (change requires restart)
# Note: Each lock table slot uses ~270 bytes of shared memory, and there are
# max_locks_per_transaction * (max_connections + max_prepared_transactions)
# lock table slots.
#max_pred_locks_per_transaction = 64 # min 10
# (change requires restart)
#------------------------------------------------------------------------------
# VERSION/PLATFORM COMPATIBILITY
#------------------------------------------------------------------------------
# - Previous PostgreSQL Versions -
#array_nulls = on
#backslash_quote = safe_encoding # on, off, or safe_encoding
#default_with_oids = off
#escape_string_warning = on
#lo_compat_privileges = off
#quote_all_identifiers = off
#sql_inheritance = on
#standard_conforming_strings = on
#synchronize_seqscans = on
# - Other Platforms and Clients -
#transform_null_equals = off
#------------------------------------------------------------------------------
# ERROR HANDLING
#------------------------------------------------------------------------------
#exit_on_error = off # terminate session on any error?
#restart_after_crash = on # reinitialize after backend crash?
#------------------------------------------------------------------------------
# CUSTOMIZED OPTIONS
#------------------------------------------------------------------------------
#custom_variable_classes = '' # list of custom variable class names
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