postgresql - 在 View 中使用 hstore 比较转储和恢复 PostgreSQL 数据库失败

Question

我有一个比较两个 hstore 列的 View 。

当我转储和恢复此数据库时，恢复失败并显示以下错误消息:

Importing /tmp/hstore_test_2014-05-12.backup...
pg_restore: [archiver (db)] Error while PROCESSING TOC:
pg_restore: [archiver (db)] Error from TOC entry 172; 1259 1358132 VIEW hstore_test_view xxxx
pg_restore: [archiver (db)] could not execute query: ERROR:  operator does not exist: public.hstore = public.hstore
LINE 2:  SELECT NULLIF(hstore_test_table.column1, hstore_test_table....
                ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
    Command was: CREATE VIEW hstore_test_view AS
 SELECT NULLIF(hstore_test_table.column1, hstore_test_table.column2) AS "nullif"
   FROM hst...
pg_restore: [archiver (db)] could not execute query: ERROR:  relation "hstore_test_schema.hstore_test_view" does not exist
    Command was: ALTER TABLE hstore_test_schema.hstore_test_view OWNER TO xxxx;

我能够通过以下步骤在 PostgreSQL 9.3.0 中创建此错误:

CREATE DATABASE hstore_test;

\c hstore_test

CREATE EXTENSION hstore WITH SCHEMA public;

CREATE SCHEMA hstore_test_schema;

CREATE TABLE hstore_test_schema.hstore_test_table(
   id int,
   column1 hstore,
   column2 hstore,
   PRIMARY KEY( id )
);

CREATE VIEW hstore_test_schema.hstore_test_view AS
SELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;

为了完整起见，转储和恢复过程如下所示:

pg_dump -U xxxx -h localhost -f /tmp/hstore_test_2014-05-12.backup -Fc hstore_test
psql -U xxxx -h localhost -d postgres -c "DROP DATABASE hstore_test"
psql -U xxxx -h localhost -d postgres -c "CREATE DATABASE hstore_test"
pg_restore -U xxxx -h localhost -d hstore_test /tmp/hstore_test_2014-05-12.backup

pg_restore -l/tmp/hstore_test_2014-05-12.backup 建议在创建 View 之前启用 hstore 扩展:

;
; Archive created at Mon May 12 11:18:32 2014
;     dbname: hstore_test
;     TOC Entries: 15
;     Compression: -1
;     Dump Version: 1.12-0
;     Format: CUSTOM
;     Integer: 4 bytes
;     Offset: 8 bytes
;     Dumped from database version: 9.3.0
;     Dumped by pg_dump version: 9.3.0
;
;
; Selected TOC Entries:
;
2074; 1262 1358002 DATABASE - hstore_test xxxx
7; 2615 1358003 SCHEMA - hstore_test_schema xxxx
5; 2615 2200 SCHEMA - public postgres
2075; 0 0 COMMENT - SCHEMA public postgres
2076; 0 0 ACL - public postgres
173; 3079 11787 EXTENSION - plpgsql 
2077; 0 0 COMMENT - EXTENSION plpgsql 
174; 3079 1358004 EXTENSION - hstore 
2078; 0 0 COMMENT - EXTENSION hstore 
171; 1259 1358124 TABLE hstore_test_schema hstore_test_table xxxx
172; 1259 1358132 VIEW hstore_test_schema hstore_test_view xxxx
2069; 0 1358124 TABLE DATA hstore_test_schema hstore_test_table xxxx
1960; 2606 1358131 CONSTRAINT hstore_test_schema hstore_test_table_pkey xxxx

顺便说一句，用 col1 = col2 替换 NULLIF(col1, col2) 似乎可以使错误消失，尽管事实上它是类型的显式比较 pg_restore 正在提示。

Answer 1

这是一个 PostgreSQL 错误。 I have relayed your report to the pgsql-bugs list .

发生的事情是 pg_dump 在您的模式中创建表时将 search_path 设置为排除 public。这个是正常的。当它转储引用不在 search_path 上的事物的对象时，它会显式地对它们进行模式限定，以便它们起作用。

它适用于 = 的情况，因为 pg_dump 看到 = 实际上是 OPERATOR(public.=)在这种情况下，并以这种形式转储它:

CREATE VIEW hstore_test_view AS
 SELECT (hstore_test_table.column1 OPERATOR(public.=) hstore_test_table.column2) AS comparison
   FROM hstore_test_table;

但是，pg_dump 无法为通过 nullif 伪函数隐式使用的运算符执行此操作。这导致以下伪命令序列:

CREATE EXTENSION IF NOT EXISTS hstore WITH SCHEMA public;
...
SET search_path = hstore_test_schema, pg_catalog;
...
CREATE VIEW hstore_test_view AS
 SELECT NULLIF(hstore_test_table.column1, hstore_test_table.column2) AS comparison
   FROM hstore_test_table;

pg_dump 仅使用 pg_catalog.pg_get_viewdef 函数转储 View ，因此这可能需要服务器后端修复。

最简单的解决方法是不使用 nullif，将其替换为更冗长但等效的 case:

CASE WHEN column1 = column2 THEN NULL ELSE column1 END;

该语法没有提供一种方法来对 nullif 伪函数的运算符进行模式限定，就像我们对显式 OPERATOR(public.=) 所做的那样，因此修复看起来并不微不足道。

我预计同样的问题会影响 GREATEST 和 LEAST，也许还会影响 DISTINCT，但事实并非如此。即使它们在运行时不在 search_path 上，两者似乎都能找到所需的运算符，但如果运算符在 View 定义时不在 search_path 上，也不会失败。这表明他们可能正在使用类型的 b-tree 运算符类来查找运算符，通过表的属性找到的目录中的类型条目。 (更新:检查了来源，是的，这就是他们所做的)。据推测 nullif 也应该这样做，但不是。

相反，它死于:

hstore_test=# \set VERBOSITY verbose
hstore_test=# CREATE VIEW hstore_test_schema.hstore_test_view AS
SELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;
ERROR:  42883: operator does not exist: public.hstore = public.hstore
LINE 2: SELECT NULLIF(column1, column2) AS comparison FROM hstore_te...
               ^
HINT:  No operator matches the given name and argument type(s). You might need to add explicit type casts.
LOCATION:  op_error, parse_oper.c:722

当我在那里设置断点时，陷阱位于:

Breakpoint 1, op_error (pstate=pstate@entry=0x1189f38, op=op@entry=0x1189c10, oprkind=oprkind@entry=98 'b', arg1=arg1@entry=97207, arg2=arg2@entry=97207, 
    fdresult=FUNCDETAIL_NOTFOUND, location=location@entry=58) at parse_oper.c:706
706     {
(gdb) bt
#0  op_error (pstate=pstate@entry=0x1189f38, op=op@entry=0x1189c10, oprkind=oprkind@entry=98 'b', arg1=arg1@entry=97207, arg2=arg2@entry=97207, fdresult=FUNCDETAIL_NOTFOUND, 
    location=location@entry=58) at parse_oper.c:706
#1  0x000000000051a81b in oper (pstate=pstate@entry=0x1189f38, opname=opname@entry=0x1189c10, ltypeId=ltypeId@entry=97207, rtypeId=rtypeId@entry=97207, 
    noError=noError@entry=0 '\000', location=location@entry=58) at parse_oper.c:440
#2  0x000000000051ad34 in make_op (pstate=pstate@entry=0x1189f38, opname=0x1189c10, ltree=ltree@entry=0x118a528, rtree=0x118a590, location=58) at parse_oper.c:770
#3  0x00000000005155e1 in transformAExprNullIf (a=0x1189bc0, pstate=0x1189f38) at parse_expr.c:1021
#4  transformExprRecurse (pstate=pstate@entry=0x1189f38, expr=0x1189bc0) at parse_expr.c:244
#5  0x0000000000517484 in transformExpr (pstate=0x1189f38, expr=<optimized out>, exprKind=exprKind@entry=EXPR_KIND_SELECT_TARGET) at parse_expr.c:116
#6  0x000000000051ff30 in transformTargetEntry (pstate=pstate@entry=0x1189f38, node=0x1189bc0, expr=expr@entry=0x0, exprKind=exprKind@entry=EXPR_KIND_SELECT_TARGET, 
    colname=0x1189ba0 "comparison", resjunk=resjunk@entry=0 '\000') at parse_target.c:94
#7  0x00000000005212df in transformTargetList (pstate=pstate@entry=0x1189f38, targetlist=<optimized out>, exprKind=exprKind@entry=EXPR_KIND_SELECT_TARGET)
    at parse_target.c:167
#8  0x00000000004ef594 in transformSelectStmt (stmt=0x11899f0, pstate=0x1189f38) at analyze.c:942
#9  transformStmt (pstate=0x1189f38, parseTree=0x11899f0) at analyze.c:243
#10 0x00000000004f0a2d in parse_analyze (parseTree=0x11899f0, 
    sourceText=sourceText@entry=0x114e6b0 "CREATE VIEW hstore_test_schema.hstore_test_view AS\nSELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;", paramTypes=paramTypes@entry=0x0, numParams=numParams@entry=0) at analyze.c:100
#11 0x000000000057cc4e in DefineView (stmt=stmt@entry=0x114f7e8, 
    queryString=queryString@entry=0x114e6b0 "CREATE VIEW hstore_test_schema.hstore_test_view AS\nSELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;") at view.c:385
#12 0x000000000065b1cf in ProcessUtilitySlow (parsetree=parsetree@entry=0x114f7e8, 
    queryString=0x114e6b0 "CREATE VIEW hstore_test_schema.hstore_test_view AS\nSELECT NULLIF(column1, column2) AS comparison FROM hstore_test_schema.hstore_test_table;", 
    context=<optimized out>, params=params@entry=0x0, completionTag=completionTag@entry=0x7fffc98c9990 "", dest=<optimized out>) at utility.c:1207
#13 0x000000000065a54e in standard_ProcessUtility (parsetree=0x114f7e8, queryString=<optimized out>, context=<optimized out>, params=0x0, dest=<optimized out>, 
    completionTag=0x7fffc98c9990 "") at utility.c:829

所以眼前的问题看起来像 transformAExprNullIf 未能通过 b-tree opclass 和类型缓存使用其操作数的类型查找运算符。