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POSTGRES中的性能問題(查詢緩慢)

2022-03-22 11:56:11 軟體設計

幾天來,我在非常具體的方面一直感到不便。例如,我們向谷歌發送某些資訊,一些檔案是根據腳本生成的。但是這個以前沒有問題,現在問題是它完成了,它創建了表,但它永遠不會完成。即表已創建并填充了資料,但它永遠不會結束。

這是查詢 https://www.mycompiler.io/view/9HIJyGPY0Pq

注意: 我放了鏈接,因為問題很長,stackoverflow 不允許更多。

但還要分析服務器端和我擁有的資源如下

  1. 作業系統:Ubuntu 服務器
  2. 記憶體:50GB
  3. 存盤:1TB
  4. CPU:16 核

我正在使用Glances進行監控,但這會發送訊息警報

Warning or critical alerts (last 2 entries)
                          2022-03-19 08:50:09 (0:00:07) - WARNING on CPU_IOWAIT (5.8)
2022-03-19 08:52:31       2022-03-19 08:17:59 (0:05:09) - CRITICAL on CPU_IOWAIT (Min:7.1 Mean:21.4 Max:31.7): kworker/u32:0, kworker/4:2, controller

這是我在 postgresql.conf 檔案中的配置

# 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
#                TB = terabytes                     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/9.6/main'     # use data in another directory
                    # (change requires restart)
hba_file = '/etc/postgresql/9.6/main/pg_hba.conf'   # host-based authentication file
                    # (change requires restart)
ident_file = '/etc/postgresql/9.6/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/9.6-main.pid'          # write an extra PID file
                    # (change requires restart)



# CONNECTIONS AND AUTHENTICATION


# - Connection Settings -

listen_addresses = '*'      # what IP address(es) to listen on;
                    # comma-separated list of addresses;
                    # defaults to 'localhost'; use '*' for all
                    # (change requires restart)
port = 5432             # (change requires restart)
max_connections = 550           # (change requires restart)
#superuser_reserved_connections = 3 # (change requires restart)
unix_socket_directories = '/var/run/postgresql' # comma-separated list of directories
                    # (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 = 'HIGH:MEDIUM: 3DES:!aNULL' # allowed SSL ciphers
                    # (change requires restart)
#ssl_prefer_server_ciphers = on     # (change requires restart)
#ssl_ecdh_curve = 'prime256v1'      # (change requires restart)
ssl_cert_file = '/etc/ssl/certs/ssl-cert-snakeoil.pem'      # (change requires restart)
ssl_key_file = '/etc/ssl/private/ssl-cert-snakeoil.key'     # (change requires restart)
#ssl_ca_file = ''           # (change requires restart)
#ssl_crl_file = ''          # (change requires restart)
#password_encryption = on
#db_user_namespace = off
#row_security = on

# GSSAPI using Kerberos
#krb_server_keyfile = ''
#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 = 20GB           # min 128kB
                    # (change requires restart)
#huge_pages = try           # on, off, or try
                    # (change requires restart)
#temp_buffers = 8MB         # min 800kB
#max_prepared_transactions = 0      # zero disables the feature
                    # (change requires restart)
# Caution: it is not advisable to set max_prepared_transactions nonzero unless
# you actively intend to use prepared transactions.
work_mem = 13107kB              # min 64kB
maintenance_work_mem = 10GB     # min 1MB
#replacement_sort_tuples = 150000   # limits use of replacement selection sort
#autovacuum_work_mem = -1       # min 1MB, or -1 to use maintenance_work_mem
#max_stack_depth = 2MB          # min 100kB
dynamic_shared_memory_type = posix  # the default is the first option
                    # supported by the operating system:
                    #   posix
                    #   sysv
                    #   windows
                    #   mmap
                    # use none to disable dynamic shared memory
                    # (change requires restart)

# - Disk -

#temp_file_limit = -1           # limits per-process temp file space
                    # in kB, or -1 for no limit

# - 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 = 0          # 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 multiplier on buffers scanned/round
#bgwriter_flush_after = 512kB       # measured in pages, 0 disables

# - Asynchronous Behavior -

effective_io_concurrency = 200      # 1-1000; 0 disables prefetching
max_worker_processes = 16       # (change requires restart)
max_parallel_workers_per_gather = 4 # taken from max_worker_processes
#old_snapshot_threshold = -1        # 1min-60d; -1 disables; 0 is immediate
                    # (change requires restart)
#backend_flush_after = 0        # measured in pages, 0 disables



# WRITE AHEAD LOG


# - Settings -

#wal_level = minimal            # minimal, replica, or logical
                    # (change requires restart)
#fsync = on             # flush data to disk for crash safety
                        # (turning this off can cause
                        # unrecoverable data corruption)
#synchronous_commit = on        # synchronization level;
                    # off, local, remote_write, remote_apply, or on
#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_compression = off          # enable compression of full-page writes
#wal_log_hints = off            # also do full page writes of non-critical updates
                    # (change requires restart)
wal_buffers = 16MB          # min 32kB, -1 sets based on shared_buffers
                    # (change requires restart)
#wal_writer_delay = 200ms       # 1-10000 milliseconds
#wal_writer_flush_after = 1MB       # measured in pages, 0 disables

#commit_delay = 0           # range 0-100000, in microseconds
#commit_siblings = 5            # range 1-1000

# - Checkpoints -

#checkpoint_timeout = 5min      # range 30s-1d
max_wal_size = 4GB
min_wal_size = 1GB
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 - 1.0
#checkpoint_flush_after = 256kB     # measured in pages, 0 disables
#checkpoint_warning = 30s       # 0 disables

# - Archiving -

#archive_mode = off     # enables archiving; off, on, or always
                # (change requires restart)
#archive_command = ''       # command to use to archive a logfile segment
                # placeholders: %p = path of file to archive
                #               %f = file name only
                # e.g. 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f'
#archive_timeout = 0        # force a logfile segment switch after this
                # number of seconds; 0 disables


#------------------------------------------------------------------------------
# REPLICATION
#------------------------------------------------------------------------------

# - Sending Server(s) -

# Set these on the master and on any standby that will send replication data.

#max_wal_senders = 0        # max number of walsender processes
                # (change requires restart)
#wal_keep_segments = 0      # in logfile segments, 16MB each; 0 disables
#wal_sender_timeout = 60s   # in milliseconds; 0 disables

#max_replication_slots = 0  # max number of replication slots
                # (change requires restart)
#track_commit_timestamp = off   # collect timestamp of transaction commit
                # (change requires restart)

# - Master Server -

# These settings are ignored on a standby server.

#synchronous_standby_names = '' # standby servers that provide sync rep
                # number of sync standbys and comma-separated list of application_name
                # from standby(s); '*' = all
#vacuum_defer_cleanup_age = 0   # number of xacts by which cleanup is delayed

# - 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
#wal_receiver_timeout = 60s     # time that receiver waits for
                    # communication from master
                    # in milliseconds; 0 disables
#wal_retrieve_retry_interval = 5s   # time to wait before retrying to
                    # retrieve WAL after a failed attempt
#------------------------------------------------------------------------------
# QUERY TUNING
#------------------------------------------------------------------------------

# - Planner Method Configuration -

#enable_bitmapscan = on
#enable_hashagg = on
#enable_hashjoin = on
#enable_indexscan = on
#enable_indexonlyscan = 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 = 1.1          # 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
#parallel_tuple_cost = 0.1      # same scale as above
#parallel_setup_cost = 1000.0   # same scale as above
#min_parallel_relation_size = 8MB
effective_cache_size = 30GB

# - 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
#force_parallel_mode = off


#------------------------------------------------------------------------------
# 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'
#syslog_sequence_numbers = on
#syslog_split_messages = on

# This is only relevant when logging to eventlog (win32):
# (change requires restart)
#event_source = 'PostgreSQL'

# - 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 = '%m [%p] %q%u@%d '            # 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
                    #   %n = timestamp with milliseconds (as a Unix epoch)
                    #   %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_replication_commands = off
#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 = 'America/Bogota'


# - Process Title -

cluster_name = '9.6/main'           # added to process titles if nonempty
                    # (change requires restart)
#update_process_title = on


#------------------------------------------------------------------------------
# RUNTIME STATISTICS
#------------------------------------------------------------------------------

# - Query/Index Statistics Collector -

#track_activities = on
#track_counts = on
#track_io_timing = off
#track_functions = none         # none, pl, all
#track_activity_query_size = 1024   # (change requires restart)
stats_temp_directory = '/var/run/postgresql/9.6-main.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_multixact_freeze_max_age = 400000000    # maximum multixact 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
#lock_timeout = 0           # in milliseconds, 0 is disabled
#idle_in_transaction_session_timeout = 0        # in milliseconds, 0 is disabled
#vacuum_freeze_min_age = 50000000
#vacuum_freeze_table_age = 150000000
#vacuum_multixact_freeze_min_age = 5000000
#vacuum_multixact_freeze_table_age = 150000000
#bytea_output = 'hex'           # hex, escape
#xmlbinary = 'base64'
#xmloption = 'content'
#gin_fuzzy_search_limit = 0
#gin_pending_list_limit = 4MB

# - Locale and Formatting -

datestyle = 'iso, dmy'
#intervalstyle = 'postgres'
timezone = 'America/Bogota'
#timezone_abbreviations = 'Default'     # Select the set of available time zone
                    # abbreviations.  Currently, there are
                    #   Default
                    #   Australia (historical usage)
                    #   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 = 'es_CO.UTF-8'         # locale for system error message
                    # strings
lc_monetary = 'es_CO.UTF-8'         # locale for monetary formatting
lc_numeric = 'es_CO.UTF-8'          # locale for number formatting
lc_time = 'es_CO.UTF-8'             # locale for time formatting

# default configuration for text search
default_text_search_config = 'pg_catalog.spanish'

# - Other Defaults -

#dynamic_library_path = '$libdir'
#local_preload_libraries = ''
#session_preload_libraries = ''


#------------------------------------------------------------------------------
# LOCK MANAGEMENT
#------------------------------------------------------------------------------

#deadlock_timeout = 1s
#max_locks_per_transaction = 64     # min 10
                    # (change requires restart)
#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
#operator_precedence_warning = 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?
#data_sync_retry = off          # retry or panic on failure to fsync
                    # data?
                    # (change requires restart)


#------------------------------------------------------------------------------
# CONFIG FILE INCLUDES
#------------------------------------------------------------------------------

# These options allow settings to be loaded from files other than the
# default postgresql.conf.  Note that these are directives, not variable
# assignments, so they can usefully be given more than once.

#include_dir = '...'            # include files ending in '.conf' from
                    # a directory, e.g., 'conf.d'
#include_if_exists = '...'      # include file only if it exists
#include = '...'            # include file


#------------------------------------------------------------------------------
# CUSTOMIZED OPTIONS
#------------------------------------------------------------------------------

# Add settings for extensions here

The version that I have of postgres is 9.6, maybe the configuration that I have in the file is not correct, but could someone tell me what other options I can explore? or look at which part I have the fault

uj5u.com熱心網友回復:

該計劃img_products_unicas用作駕駛表,引擎正在閱讀它;那一定很慢。

我的猜測是 usingproducts可能會更好,因為它有兩個過濾謂詞。如果您同意,您可以使用一些技巧:

  1. 確保存在以下索引:

    • 產品(狀態、價格)
    • 檔案(product_id,主要)
    • img_products_unicas (product_id)
    • 類別(category_id)——我猜這個存在
  2. 如果查詢仍然選擇img_products_unicas作為驅動表,請嘗試將連接謂詞(通過添加 0 * f.product_id)更改為:

     INNER join img_products_unicas t4 on p.product_id   0 * f.product_id = t4.product_id
    

最重要的是,您應該確保表格的統計資訊是最新的。ANALYZE如果您還沒有這樣做,請在查詢中提到的每個表上使用。

轉載請註明出處,本文鏈接:https://www.uj5u.com/ruanti/446062.html

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  • 面試突擊第一季,第二季,第三季

    第一季必考 https://www.bilibili.com/video/BV1FE411y79Y?from=search&seid=15921726601957489746 第二季分布式 https://www.bilibili.com/video/BV13f4y127ee/?spm_id_fro ......

    uj5u.com 2020-09-10 05:35:24 more
  • 第三單元作業總結

    1.前言 這應該是本學期最后一次寫作業總結了吧。總體來說,對作業的節奏也差不多掌握了,作業做起來的效率也更高了。雖然和之前的作業一樣,作業中都要用到新的知識,但是相比之前,更加懂得了如何利用工具以及資料。雖然之間卡過殼,但總體而言,這幾次作業還算完成的比較好。 2.作業程序總結 相比前兩個單元,此單 ......

    uj5u.com 2020-09-10 05:35:41 more
  • 北航OO(2020)第四單元博客作業暨課程總結博客

    北航OO(2020)第四單元博客作業暨課程總結博客 本單元作業的架構設計 在本單元中,由于UML圖具有比較清晰的樹形結構,因此我對其中需要進行查詢操作的元素進行了包裝,在樹的父節點中存盤所有孩子的參考。考慮到性能問題,我采用了快取機制,一次查詢后盡可能快取已經遍歷過的資訊,以減少遍歷次數。 本單元我 ......

    uj5u.com 2020-09-10 05:35:48 more
  • BUAA_OO_第四單元

    一、UML決議器設計 ? 先看下題目:第四單元實作一個基于JDK 8帶有效性檢查的UML(Unified Modeling Language)類圖,順序圖,狀態圖分析器 MyUmlInteraction,實際上我們要建立一個有向圖模型,UML中的物件(元素)可能與同級元素連接,也可與低級元素相連形成 ......

    uj5u.com 2020-09-10 05:35:54 more
  • 6.1邏輯運算子

    邏輯運算子 1. && 短路與 運算式1 && 運算式2 01.運算式1為true并且運算式2也為true 整體回傳為true 02.運算式1為false,將不會執行運算式2 整體回傳為false 03.只要有一個運算式為false 整體回傳為false 2. || 短路或 運算式1 || 運算式2 ......

    uj5u.com 2020-09-10 05:35:56 more
  • BUAAOO 第四單元 & 課程總結

    1. 第四單元:StarUml檔案決議 本單元采用了圖模型決議UML。 UML檔案可以抽象為圖、子圖、邊的邏輯結構。 在實作中,圖的節點包括類、介面、屬性,子圖包括狀態圖、順序圖等。 采用了三次遍歷UML元素的方法建圖,第一遍遍歷建點,第二、三次遍歷設定屬性、連邊,實作圖物件的初始化。這里借鑒了一些 ......

    uj5u.com 2020-09-10 05:36:06 more
  • 談談我對C# 多型的理解

    面向物件三要素:封裝、繼承、多型。 封裝和繼承,這兩個比較好理解,但要理解多型的話,可就稍微有點難度了。今天,我們就來講講多型的理解。 我們應該經常會看到面試題目:請談談對多型的理解。 其實呢,多型非常簡單,就一句話:呼叫同一種方法產生了不同的結果。 具體實作方式有三種。 一、多載 多載很簡單。 p ......

    uj5u.com 2020-09-10 05:36:09 more
  • Python 資料驅動工具:DDT

    背景 python 的unittest 沒有自帶資料驅動功能。 所以如果使用unittest,同時又想使用資料驅動,那么就可以使用DDT來完成。 DDT是 “Data-Driven Tests”的縮寫。 資料:http://ddt.readthedocs.io/en/latest/ 使用方法 dd. ......

    uj5u.com 2020-09-10 05:36:13 more
  • Python里面的xlrd模塊詳解

    那我就一下面積個問題對xlrd模塊進行學習一下: 1.什么是xlrd模塊? 2.為什么使用xlrd模塊? 3.怎樣使用xlrd模塊? 1.什么是xlrd模塊? ?python操作excel主要用到xlrd和xlwt這兩個庫,即xlrd是讀excel,xlwt是寫excel的庫。 今天就先來說一下xl ......

    uj5u.com 2020-09-10 05:36:28 more
  • 當我們創建HashMap時,底層到底做了什么?

    jdk1.7中的底層實作程序(底層基于陣列+鏈表) 在我們new HashMap()時,底層創建了默認長度為16的一維陣列Entry[ ] table。當我們呼叫map.put(key1,value1)方法向HashMap里添加資料的時候: 首先,呼叫key1所在類的hashCode()計算key1 ......

    uj5u.com 2020-09-10 05:36:38 more
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  • 【中介者設計模式詳解】C/Java/JS/Go/Python/TS不同語言實作

    * 中介者模式是一種行為型設計模式,它可以用來減少類之間的直接依賴關系,
    * 將物件之間的通信封裝到一個中介者物件中,從而使得各個物件之間的關系更加松散。
    * 在中介者模式中,物件之間不再直接相互互動,而是通過中介者來中轉訊息。 ......

    uj5u.com 2023-04-20 08:20:47 more
  • 露天煤礦現場調研和交流案例分享

    他們集團的資訊化公司及研究院在一個礦區正在做智能礦山的統一平臺的 試點,專案投資大概1億,包括了礦山的各方面的內容,顯示得我們這次交流有點多余。他們2年前開始做智能礦山的規劃,有很多煤礦行業專家的加持,他們的描述是非常完美,但是去年底應該上線的平臺,現在還沒有看到影子。他們確實有很多場景需求,但是被... ......

    uj5u.com 2023-04-20 08:20:25 more
  • 《社區人員管理》實戰案例設計&個人案例分享

    設計是一個讓人夢想成真程序,開始編碼、測驗、除錯之前進行需求分析和架構設計,才能保證關鍵方面都做正確 ......

    uj5u.com 2023-04-20 08:20:17 more
  • 軟體架構生態化-多角色交付的探索實踐

    作為一個技術架構師,不僅僅要緊跟行業技術趨勢,還要結合研發團隊現狀及痛點,探索新的交付方案。在日常中,你是否遇到如下問題 “ 業務需求排期長研發是瓶頸;非研發角色感受不到研發技改提效的變化;引入ISV 團隊又擔心質量和安全,培訓周期長“等等,基于此我們探索了一種新的技術體系及交付方案來解決如上問題。 ......

    uj5u.com 2023-04-20 08:20:10 more
  • 【中介者設計模式詳解】C/Java/JS/Go/Python/TS不同語言實作

    * 中介者模式是一種行為型設計模式,它可以用來減少類之間的直接依賴關系,
    * 將物件之間的通信封裝到一個中介者物件中,從而使得各個物件之間的關系更加松散。
    * 在中介者模式中,物件之間不再直接相互互動,而是通過中介者來中轉訊息。 ......

    uj5u.com 2023-04-20 08:19:44 more
  • 露天煤礦現場調研和交流案例分享

    他們集團的資訊化公司及研究院在一個礦區正在做智能礦山的統一平臺的 試點,專案投資大概1億,包括了礦山的各方面的內容,顯示得我們這次交流有點多余。他們2年前開始做智能礦山的規劃,有很多煤礦行業專家的加持,他們的描述是非常完美,但是去年底應該上線的平臺,現在還沒有看到影子。他們確實有很多場景需求,但是被... ......

    uj5u.com 2023-04-20 08:19:07 more
  • 《社區人員管理》實戰案例設計&個人案例分享

    設計是一個讓人夢想成真程序,開始編碼、測驗、除錯之前進行需求分析和架構設計,才能保證關鍵方面都做正確 ......

    uj5u.com 2023-04-20 08:18:57 more
  • 軟體架構生態化-多角色交付的探索實踐

    作為一個技術架構師,不僅僅要緊跟行業技術趨勢,還要結合研發團隊現狀及痛點,探索新的交付方案。在日常中,你是否遇到如下問題 “ 業務需求排期長研發是瓶頸;非研發角色感受不到研發技改提效的變化;引入ISV 團隊又擔心質量和安全,培訓周期長“等等,基于此我們探索了一種新的技術體系及交付方案來解決如上問題。 ......

    uj5u.com 2023-04-20 08:18:49 more
  • 05單件模式

    #經典的單件模式 public class Singleton { private static Singleton uniqueInstance; //一個靜態變數持有Singleton類的唯一實體。 // 其他有用的實體變數寫在這里 //構造器宣告為私有,只有Singleton可以實體化這個類! ......

    uj5u.com 2023-04-19 08:42:51 more
  • 【架構與設計】常見微服務分層架構的區別和落地實踐

    軟體工程的方方面面都遵循一個最基本的道理:沒有銀彈,架構分層模型更是如此,每一種都有各自優缺點,所以請根據不同的業務場景,并遵循簡單、可演進這兩個重要的架構原則選擇合適的架構分層模型即可。 ......

    uj5u.com 2023-04-19 08:42:41 more