PostgreSQL 函數調試 & auto_explain

作者

digoal

日期

2016-11-21

標簽

PostgreSQL , pldebugger , 函數調試 , auto_explain

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背景

PostgreSQL的服務端編程能力比較強，不僅支持像java, R, python這種流行的編程語言，另外還內置了一個與Oracle plsql功能幾乎一致的plpgsql語言。

對于開發人員來說，有了語言還不夠的，調試是非常常見的需求。

所以PostgreSQL的函數語言怎么調試呢，使用pldebugger即可。

pldebugger的安裝

https://git.postgresql.org/gitweb/?p=pldebugger.git;a=summary

plpgsql調試方法

https://www.pgadmin.org/docs/1.22/debugger.html

除了函數的調試，還有函數內SQL的執行計劃如何觀測。

auto_explain

auto_explain 一個比較給力的模塊.

用于向日志輸出超出定義閾值執行時間的SQL的執行計劃。更強大的是可以選擇是否輸出內嵌SQL的執行計劃(如函數中的SQL).

auto_explain的輸出更詳細的解釋可以參考EXPLAIN的解釋。或者man EXPLAIN.

SYNOPSIS EXPLAIN [ ( option [, ...] ) ] statement EXPLAIN [ ANALYZE ] [ VERBOSE ] statement where option can be one of: ANALYZE [ boolean ] VERBOSE [ boolean ] COSTS [ boolean ] BUFFERS [ boolean ] FORMAT { TEXT | XML | JSON | YAML }

開啟方式有兩種 :

1. 通過配置文件postgresql.conf

需要重啟數據庫。

2. 通過LOAD 'auto_explain';

這個只在當前SESSION生效，不需要重啟數據庫, 需要超級用戶權限。

其實還可以設置local_preload_libraries，session_preload_libraries參數來啟用。

例子

1. 修改配置文件:

shared_preload_libraries = 'auto_explain'

新增如下配置:

auto_explain.log_min_duration = 0 # 為了方便查看,這里把時間設置為0,所有SQL都會被auto_explain捕獲輸出.實際使用的時候適當調大。如 100ms auto_explain.log_analyze = true # 以下可選 auto_explain.log_verbose = true auto_explain.log_buffers = true auto_explain.log_nested_statements = true

然后重啟數據庫.重啟時會輸出一個LOG

postgres@db5-> LOG: loaded library "$libdir/auto_explain.so"

下面來執行幾條SQL

postgres@db5-> psql -h 127.0.0.1 digoal digoal psql (9.1beta1) Type "help" for help. digoal=> select * from tbl_user_info limit 2; id | firstname | lastname | corp ----+-----------+----------+---------- 1 | zhou1 | digoal1 | sky-mobi 2 | zhou2 | digoal2 | sky-mobi (2 rows) digoal=> select count(*) from tbl_test; count --------- 1000100 (1 row)

日志輸出

2011-06-08 15:19:14.390 CST,"digoal","digoal",13789,"127.0.0.1:59549",4def2270.35dd,1,"SELECT",2011-06-08 15:19:12 CST,2/18,0,LOG,00 000,"duration: 0.040 ms plan: Query Text: select * from tbl_user_info limit 2; Limit (cost=0.00..0.04 rows=2 width=31) (actual time=0.020..0.023 rows=2 loops=1) Output: id, firstname, lastname, corp Buffers: shared hit=1 -> Seq Scan on public.tbl_user_info (cost=0.00..183.00 rows=10000 width=31) (actual time=0.014..0.015 rows=2 loops=1) Output: id, firstname, lastname, corp Buffers: shared hit=1",,,,,,,,,"psql" 2011-06-08 15:19:17.902 CST,"digoal","digoal",13789,"127.0.0.1:59549",4def2270.35dd,2,"SELECT",2011-06-08 15:19:12 CST,2/19,0,LOG,00 000,"duration: 1232.064 ms plan: Query Text: select count(*) from tbl_test; Aggregate (cost=16927.25..16927.26 rows=1 width=0) (actual time=1232.044..1232.045 rows=1 loops=1) Output: count(*) Buffers: shared hit=4426 -> Seq Scan on public.tbl_test (cost=0.00..14427.00 rows=1000100 width=0) (actual time=0.015..626.872 rows=1000100 loops=1) Output: id Buffers: shared hit=4426",,,,,,,,,"psql"

2. 通過LOAD 'auto_explain' ;

這個只在當前SESSION生效，不需要重啟數據庫, 需要超級用戶權限。

首先先恢復postgresql.conf的配置，去除前面的配置.然后重啟數據庫.

普通用戶不允許加載auto_explain模塊.(普通用戶只允許加載$libdir/plugins目錄下的模塊,但是auto_explain即使拷貝到這個目錄也不行)

digoal=> load 'auto_explain'; ERROR: access to library "auto_explain" is not allowed digoal=> \c digoal postgres You are now connected to database "digoal" as user "postgres". digoal=# load 'auto_explain'; LOAD digoal=# set auto_explain.log_min_duration=0; SET digoal=# select * from tbl_user_info limit 2; id | firstname | lastname | corp ----+-----------+----------+---------- 1 | zhou1 | digoal1 | sky-mobi 2 | zhou2 | digoal2 | sky-mobi (2 rows)

查看日志

2011-06-08 15:25:33.361 CST,"postgres","digoal",13968,"127.0.0.1:15445",4def23d5.3690,1,"SELECT",2011-06-08 15:25:09 CST,2/9,0,LOG,0 0000,"duration: 0.048 ms plan: Query Text: select * from tbl_user_info limit 2; Limit (cost=0.00..0.04 rows=2 width=31) -> Seq Scan on tbl_user_info (cost=0.00..183.00 rows=10000 width=31)",,,,,,,,,"psql"

連接到digoal用戶，這個LOAD的模塊消失(后面會有解釋).

digoal=# load 'auto_explain'; LOAD digoal=# set session auto_explain.log_min_duration=0; SET digoal=# \c digoal digoal You are now connected to database "digoal" as user "digoal". digoal=> select * from tbl_user_info limit 3; id | firstname | lastname | corp ----+-----------+----------+---------- 1 | zhou1 | digoal1 | sky-mobi 2 | zhou2 | digoal2 | sky-mobi 3 | zhou3 | digoal3 | sky-mobi (3 rows)

查看日志，沒有auto_explain的輸出.即使這里使用了session來定義這個參數的有效范圍。

原因是session重新分配了，因為\c digoal digoal 相當于重新連接，backend也重新生成,如下.

digoal=> select * from pg_stat_activity; datid | datname | procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_s tart | xact_start | query_start | waiting | current_query -------+---------+---------+----------+---------+------------------+-------------+-----------------+-------------+------------------ -------------+-------------------------------+-------------------------------+---------+--------------------------------- 16430 | digoal | 14155 | 16423 | digoal | psql | 127.0.0.1 | | 5959 | 2011-06-08 15:31: 32.794906+08 | 2011-06-08 15:31:40.616346+08 | 2011-06-08 15:31:40.616346+08 | f | select * from pg_stat_activity; (1 row) digoal=> \c digoal postgres You are now connected to database "digoal" as user "postgres". digoal=# select * from pg_stat_activity; datid | datname | procpid | usesysid | usename | application_name | client_addr | client_hostname | client_port | backend_ start | xact_start | query_start | waiting | current_query -------+---------+---------+----------+----------+------------------+-------------+-----------------+-------------+----------------- --------------+-------------------------------+-------------------------------+---------+--------------------------------- 16430 | digoal | 14161 | 10 | postgres | psql | 127.0.0.1 | | 5961 | 2011-06-08 15:31 :43.937297+08 | 2011-06-08 15:31:45.178005+08 | 2011-06-08 15:31:45.178005+08 | f | select * from pg_stat_activity; (1 row)

那么如何避免這樣的情況發生呢? 答案是使用set role .

digoal=# load 'auto_explain'; LOAD digoal=# set session auto_explain.log_min_duration=0; SET digoal=# set role digoal; SET digoal=> select * from tbl_user_info limit 3; id | firstname | lastname | corp ----+-----------+----------+---------- 1 | zhou1 | digoal1 | sky-mobi 2 | zhou2 | digoal2 | sky-mobi 3 | zhou3 | digoal3 | sky-mobi (3 rows)

再看日志,已經有了 :

2011-06-08 15:29:30.011 CST,"postgres","digoal",14062,"127.0.0.1:5939",4def24bc.36ee,1,"SELECT",2011-06-08 15:29:00 CST,2/29,0,LOG,0 0000,"duration: 0.031 ms plan: Query Text: select * from tbl_user_info limit 3; Limit (cost=0.00..0.05 rows=3 width=31) -> Seq Scan on tbl_user_info (cost=0.00..183.00 rows=10000 width=31)",,,,,,,,,"psql"

如果你不想看日志這么麻煩，想在client直接顯示，也很方便，設置client_min_messages='log'就可以看到auto explain的輸出了。

set client_min_messages='log'; set auto_explain.log_min_duration = 0; set auto_explain.log_analyze = true; set auto_explain.log_verbose = true; set auto_explain.log_buffers = true; set auto_explain.log_nested_statements = true;postgres=# do language plpgsql $$ declare begin perform 1 from pg_class where oid=1; end; $$;LOG: duration: 0.008 ms plan: Query Text: SELECT 1 from pg_class where oid=1 Index Only Scan using pg_class_oid_index on pg_catalog.pg_class (cost=0.27..1.29 rows=1 width=4) (actual time=0.006..0.006 rows=0 loops=1)Output: 1Index Cond: (pg_class.oid = '1'::oid)Heap Fetches: 0Buffers: shared hit=2 DO

參考

1. man LOAD

2. man EXPLAIN

3.?http://www.postgresql.org/docs/9.6/static/auto-explain.html

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