Re: PostgreSQL vs oracle doing 1 million sqrts am I doing it wrong? - Mailing list pgsql-hackers

Thanks to all for the great info.  We are new to postgresql and this discussion has both instructed us and increased
ourrespect for the database and the community.
 

I am seeing a behavior that I don’t understand and hopefully you guys can clear it up.

I am using AWS postgresql db.m3.2xlarge and using pgadmin III 1.18 comparing against AWS oracle on db.m3.2xlarge using
sqldeveloper and TOAD.
 

I am running a query with 30 tables in the from clause, getting 137 columns back (this is our most basic query, they
geta lot more more complex).   It returns back 4800 rows.
 

In oracle 1st run takes 3.92 seconds, 2nd .38 seconds.  Scrolling to end takes and extra 1.5 seconds for total of 5.5.

Using pgadmin, I run the query.  Looking at the lower right hand I can see the time going up.  It stops at 8200 ms or
closeto it every time, then it takes an extra 6 seconds before it displays the rows on the screen.  2nd, 3rd, etc. runs
alltake about  same amount of time 8 sec plus 6 sec
 

I then changed it to return only 1 column back.   In oracle/sqldeveloper identical behavior as before, same time.  In
postgresqlit now goes down to 1.8 seconds for 1st, 2nd, etc. runs.
 

I then change it so that I am asking for the sum of 1 column.  In oracle time goes down to .2 seconds and postgresql
nowgoes down to .2 seconds also.
 

I then change it back to get the full result set and behavior goes back to original, oracle .38 since its cached,
postgresql8 seconds.
 

Of the 30 tables 6 are 10-50 gigs in size.  Our  setting are

"shared_buffers";"7639832kB"
"effective_cache_size";"15279664kB"
"allow_system_table_mods";"off"
"application_name";"pgAdmin III - Query Tool"
"archive_command";"/etc/rds/dbbin/pgscripts/rds_wal_archive %p"
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"archive_timeout";"5min"
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"autovacuum";"on"
"autovacuum_analyze_scale_factor";"0.1"
"autovacuum_analyze_threshold";"50"
"autovacuum_freeze_max_age";"200000000"
"autovacuum_max_workers";"3"
"autovacuum_multixact_freeze_max_age";"400000000"
"autovacuum_naptime";"1min"
"autovacuum_vacuum_cost_delay";"20ms"
"autovacuum_vacuum_cost_limit";"-1"
"autovacuum_vacuum_scale_factor";"0.2"
"autovacuum_vacuum_threshold";"50"
"backslash_quote";"safe_encoding"
"bgwriter_delay";"200ms"
"bgwriter_lru_maxpages";"100"
"bgwriter_lru_multiplier";"2"
"block_size";"8192"
"bonjour";"off"
"bonjour_name";""
"bytea_output";"escape"
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"checkpoint_completion_target";"0.9"
"checkpoint_segments";"16"
"checkpoint_timeout";"5min"
"checkpoint_warning";"30s"
"client_encoding";"UNICODE"
"client_min_messages";"notice"
"commit_delay";"0"
"commit_siblings";"5"
"constraint_exclusion";"partition"
"cpu_index_tuple_cost";"0.005"
"cpu_operator_cost";"0.0025"
"cpu_tuple_cost";"0.01"
"cursor_tuple_fraction";"0.1"
"DateStyle";"ISO, MDY"
"db_user_namespace";"off"
"deadlock_timeout";"1s"
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"debug_print_plan";"off"
"debug_print_rewritten";"off"
"default_statistics_target";"100"
"default_tablespace";""
"default_text_search_config";"pg_catalog.simple"
"default_transaction_deferrable";"off"
"default_transaction_isolation";"read committed"
"default_transaction_read_only";"off"
"default_with_oids";"off"
"effective_cache_size";"15279664kB"
"effective_io_concurrency";"1"
"enable_bitmapscan";"on"
"enable_hashagg";"on"
"enable_hashjoin";"on"
"enable_indexonlyscan";"on"
"enable_indexscan";"on"
"enable_material";"on"
"enable_mergejoin";"on"
"enable_nestloop";"on"
"enable_seqscan";"on"
"enable_sort";"on"
"enable_tidscan";"on"
"escape_string_warning";"on"
"event_source";"PostgreSQL"
"exit_on_error";"off"
"extra_float_digits";"0"
"from_collapse_limit";"8"
"fsync";"on"
"full_page_writes";"on"
"geqo";"on"
"geqo_effort";"5"
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"geqo_pool_size";"0"
"geqo_seed";"0"
"geqo_selection_bias";"2"
"geqo_threshold";"12"
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"integer_datetimes";"on"
"IntervalStyle";"postgres"
"join_collapse_limit";"8"
"krb_caseins_users";"off"
"krb_srvname";"postgres"
"lc_collate";"en_US.UTF-8"
"lc_ctype";"en_US.UTF-8"
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"lc_monetary";"C"
"lc_numeric";"C"
"lc_time";"C"
"listen_addresses";"*"
"lo_compat_privileges";"off"
"local_preload_libraries";""
"lock_timeout";"0"
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"log_destination";"stderr"
"log_disconnections";"off"
"log_duration";"off"
"log_error_verbosity";"default"
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"log_line_prefix";"%t:%r:%u@%d:[%p]:"
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"log_min_error_statement";"error"
"log_min_messages";"warning"
"log_parser_stats";"off"
"log_planner_stats";"off"
"log_rotation_age";"1h"
"log_rotation_size";"10MB"
"log_statement";"none"
"log_statement_stats";"off"
"log_temp_files";"-1"
"log_timezone";"UTC"
"log_truncate_on_rotation";"off"
"logging_collector";"on"
"maintenance_work_mem";"16MB"
"max_connections";"2486"
"max_files_per_process";"1000"
"max_function_args";"100"
"max_identifier_length";"63"
"max_index_keys";"32"
"max_locks_per_transaction";"64"
"max_pred_locks_per_transaction";"64"
"max_prepared_transactions";"0"
"max_stack_depth";"6MB"
"max_standby_archive_delay";"30s"
"max_standby_streaming_delay";"30s"
"max_wal_senders";"0"
"password_encryption";"on"
"port";"5432"
"post_auth_delay";"0"
"pre_auth_delay";"0"
"quote_all_identifiers";"off"
"random_page_cost";"4"
"restart_after_crash";"on"
"search_path";""$user",public"
"segment_size";"1GB"
"seq_page_cost";"1"
"server_encoding";"UTF8"
"server_version";"9.3.3"
"server_version_num";"90303"
"session_replication_role";"origin"
"shared_buffers";"7639832kB"
"sql_inheritance";"on"
"ssl";"on"
"ssl_ca_file";"/rdsdbdata/rds-metadata/ca-cert.pem"
"ssl_cert_file";"/rdsdbdata/rds-metadata/server-cert.pem"
"ssl_crl_file";""
"ssl_key_file";"/rdsdbdata/rds-metadata/server-key.pem"
"ssl_renegotiation_limit";"512MB"
"standard_conforming_strings";"on"
"statement_timeout";"0"
"superuser_reserved_connections";"3"
"synchronize_seqscans";"on"
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"synchronous_standby_names";""
"syslog_facility";"local0"
"syslog_ident";"postgres"
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"tcp_keepalives_idle";"300"
"tcp_keepalives_interval";"30"
"temp_buffers";"8MB"
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"TimeZone";"UTC"
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"transaction_isolation";"read committed"
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"vacuum_cost_limit";"200"
"vacuum_cost_page_dirty";"20"
"vacuum_cost_page_hit";"1"
"vacuum_cost_page_miss";"10"
"vacuum_defer_cleanup_age";"0"
"vacuum_freeze_min_age";"50000000"
"vacuum_freeze_table_age";"150000000"
"vacuum_multixact_freeze_min_age";"5000000"
"vacuum_multixact_freeze_table_age";"150000000"
"wal_block_size";"8192"
"wal_buffers";"16MB"
"wal_keep_segments";"0"
"wal_level";"archive"
"wal_receiver_status_interval";"10s"
"wal_receiver_timeout";"1min"
"wal_segment_size";"16MB"
"wal_sender_timeout";"1min"
"wal_sync_method";"fdatasync"
"wal_writer_delay";"200ms"
"work_mem";"1MB"
"xmlbinary";"base64"
"xmloption";"content"
"zero_damaged_pages";"off"
-----Original Message-----
From: Josh Berkus [mailto:josh@agliodbs.com] 
Sent: Thursday, August 07, 2014 7:14 PM
To: Tom Lane; James Cloos
Cc: pgsql-hackers@postgresql.org; Shaun Thomas; Mark Kirkwood; Ramirez, Danilo
Subject: Re: [HACKERS] PostrgeSQL vs oracle doing 1 million sqrts am I doing it wrong?

On 08/07/2014 04:48 PM, Tom Lane wrote:
> plpgsql is not efficient at all about coercions performed as a side 
> effect of assignments; if memory serves, it always handles them by 
> converting to text and back.  So basically the added cost here came 
> from float8out() and float4in().  There has been some talk of trying 
> to do such coercions via SQL casts, but nothing's been done for fear 
> of compatibility problems.

Yeah, that's a weeks-long project for someone.  And would require a lot of tests ...

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com