1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
|
-- tests for tidscans
CREATE TABLE tidscan(id integer);
-- only insert a few rows, we don't want to spill onto a second table page
INSERT INTO tidscan VALUES (1), (2), (3);
-- show ctids
SELECT ctid, * FROM tidscan;
ctid | id
-------+----
(0,1) | 1
(0,2) | 2
(0,3) | 3
(3 rows)
-- ctid equality - implemented as tidscan
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,1)';
QUERY PLAN
-----------------------------------
Tid Scan on tidscan
TID Cond: (ctid = '(0,1)'::tid)
(2 rows)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,1)';
ctid | id
-------+----
(0,1) | 1
(1 row)
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
QUERY PLAN
-----------------------------------
Tid Scan on tidscan
TID Cond: ('(0,1)'::tid = ctid)
(2 rows)
SELECT ctid, * FROM tidscan WHERE '(0,1)' = ctid;
ctid | id
-------+----
(0,1) | 1
(1 row)
-- OR'd clauses
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
QUERY PLAN
--------------------------------------------------------------
Tid Scan on tidscan
TID Cond: ((ctid = '(0,2)'::tid) OR ('(0,1)'::tid = ctid))
(2 rows)
SELECT ctid, * FROM tidscan WHERE ctid = '(0,2)' OR '(0,1)' = ctid;
ctid | id
-------+----
(0,1) | 1
(0,2) | 2
(2 rows)
-- ctid = ScalarArrayOp - implemented as tidscan
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
QUERY PLAN
-------------------------------------------------------
Tid Scan on tidscan
TID Cond: (ctid = ANY ('{"(0,1)","(0,2)"}'::tid[]))
(2 rows)
SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
ctid | id
-------+----
(0,1) | 1
(0,2) | 2
(2 rows)
-- ctid != ScalarArrayOp - can't be implemented as tidscan
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan WHERE ctid != ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
QUERY PLAN
------------------------------------------------------
Seq Scan on tidscan
Filter: (ctid <> ANY ('{"(0,1)","(0,2)"}'::tid[]))
(2 rows)
SELECT ctid, * FROM tidscan WHERE ctid != ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
ctid | id
-------+----
(0,1) | 1
(0,2) | 2
(0,3) | 3
(3 rows)
-- tid equality extracted from sub-AND clauses
EXPLAIN (COSTS OFF)
SELECT ctid, * FROM tidscan
WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
QUERY PLAN
--------------------------------------------------------------------------------------------------------------
Tid Scan on tidscan
TID Cond: ((ctid = ANY ('{"(0,2)","(0,3)"}'::tid[])) OR (ctid = '(0,1)'::tid))
Filter: (((id = 3) AND (ctid = ANY ('{"(0,2)","(0,3)"}'::tid[]))) OR ((ctid = '(0,1)'::tid) AND (id = 1)))
(3 rows)
SELECT ctid, * FROM tidscan
WHERE (id = 3 AND ctid IN ('(0,2)', '(0,3)')) OR (ctid = '(0,1)' AND id = 1);
ctid | id
-------+----
(0,1) | 1
(0,3) | 3
(2 rows)
-- nestloop-with-inner-tidscan joins on tid
EXPLAIN (COSTS OFF)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
QUERY PLAN
------------------------------------
Nested Loop
-> Seq Scan on tidscan t1
Filter: (id = 1)
-> Tid Scan on tidscan t2
TID Cond: (ctid = t1.ctid)
(5 rows)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
ctid | id | ctid | id
-------+----+-------+----
(0,1) | 1 | (0,1) | 1
(1 row)
EXPLAIN (COSTS OFF)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
QUERY PLAN
------------------------------------
Nested Loop Left Join
-> Seq Scan on tidscan t1
Filter: (id = 1)
-> Tid Scan on tidscan t2
TID Cond: (t1.ctid = ctid)
(5 rows)
SELECT t1.ctid, t1.*, t2.ctid, t2.*
FROM tidscan t1 LEFT JOIN tidscan t2 ON t1.ctid = t2.ctid WHERE t1.id = 1;
ctid | id | ctid | id
-------+----+-------+----
(0,1) | 1 | (0,1) | 1
(1 row)
-- exercise backward scan and rewind
BEGIN;
DECLARE c CURSOR FOR
SELECT ctid, * FROM tidscan WHERE ctid = ANY(ARRAY['(0,1)', '(0,2)']::tid[]);
FETCH ALL FROM c;
ctid | id
-------+----
(0,1) | 1
(0,2) | 2
(2 rows)
FETCH BACKWARD 1 FROM c;
ctid | id
-------+----
(0,2) | 2
(1 row)
FETCH FIRST FROM c;
ctid | id
-------+----
(0,1) | 1
(1 row)
ROLLBACK;
-- tidscan via CURRENT OF
BEGIN;
DECLARE c CURSOR FOR SELECT ctid, * FROM tidscan;
FETCH NEXT FROM c; -- skip one row
ctid | id
-------+----
(0,1) | 1
(1 row)
FETCH NEXT FROM c;
ctid | id
-------+----
(0,2) | 2
(1 row)
-- perform update
EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
UPDATE tidscan SET id = -id WHERE CURRENT OF c RETURNING *;
QUERY PLAN
---------------------------------------------------
Update on tidscan (actual rows=1 loops=1)
-> Tid Scan on tidscan (actual rows=1 loops=1)
TID Cond: CURRENT OF c
(3 rows)
FETCH NEXT FROM c;
ctid | id
-------+----
(0,3) | 3
(1 row)
-- perform update
EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
UPDATE tidscan SET id = -id WHERE CURRENT OF c RETURNING *;
QUERY PLAN
---------------------------------------------------
Update on tidscan (actual rows=1 loops=1)
-> Tid Scan on tidscan (actual rows=1 loops=1)
TID Cond: CURRENT OF c
(3 rows)
SELECT * FROM tidscan;
id
----
1
-2
-3
(3 rows)
-- position cursor past any rows
FETCH NEXT FROM c;
ctid | id
------+----
(0 rows)
-- should error out
EXPLAIN (ANALYZE, COSTS OFF, SUMMARY OFF, TIMING OFF)
UPDATE tidscan SET id = -id WHERE CURRENT OF c RETURNING *;
ERROR: cursor "c" is not positioned on a row
ROLLBACK;
DROP TABLE tidscan;
|
