Fix shameful bug with maximum item size in entry tree

RUM posting trees received rightbound keys.  Accidentally RumMaxItemSize
was corrected according to this.  However RumMaxItemSize is related only
to entry tree which wasn't changed.  That cause long standing bug that long
lexemes can't fit entry tree.  Bug is fixed in this commit.  Also regression
test were added for longest lexemes with longest positions lists.

Makefile

@@ -12,7 +12,7 @@ DATA = rum--1.0.sql
 PGFILEDESC = "RUM index access method"
 
 REGRESS = rum rum_hash ruminv timestamp orderby orderby_hash altorder \
-	altorder_hash
+	altorder_hash limits
 
 LDFLAGS_SL += $(filter -lm, $(LIBS))
 

expected/limits.out

@@ -0,0 +1,162 @@
+-- Check we can put and query lexemes of maximum size 2046 bytes
+-- with maximum posting list size.
+CREATE TABLE limits_test (v tsvector);
+INSERT INTO limits_test (SELECT (SELECT (repeat(chr(65 + num % 26), 2046) || ':' || string_agg(i::text, ','))::tsvector FROM generate_series(1,1024) i) FROM generate_series(1,1000) num);
+CREATE INDEX limits_test_idx ON limits_test USING rum (v);
+SET enable_seqscan = off;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('A', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('B', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('C', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('D', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('E', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('F', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('G', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('H', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('I', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('J', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('K', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('L', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('M', 2046)::tsquery;
+ count 
+-------
+    39
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('N', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('O', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('P', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('Q', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('R', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('S', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('T', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('U', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('V', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('W', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('X', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('Y', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('Z', 2046)::tsquery;
+ count 
+-------
+    38
+(1 row)
+

sql/limits.sql

@@ -0,0 +1,33 @@
+-- Check we can put and query lexemes of maximum size 2046 bytes
+-- with maximum posting list size.
+CREATE TABLE limits_test (v tsvector);
+INSERT INTO limits_test (SELECT (SELECT (repeat(chr(65 + num % 26), 2046) || ':' || string_agg(i::text, ','))::tsvector FROM generate_series(1,1024) i) FROM generate_series(1,1000) num);
+CREATE INDEX limits_test_idx ON limits_test USING rum (v);
+
+SET enable_seqscan = off;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('A', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('B', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('C', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('D', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('E', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('F', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('G', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('H', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('I', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('J', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('K', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('L', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('M', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('N', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('O', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('P', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('Q', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('R', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('S', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('T', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('U', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('V', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('W', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('X', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('Y', 2046)::tsquery;
+SELECT COUNT(*) FROM limits_test WHERE v @@ repeat('Z', 2046)::tsquery;

src/rum.h

@@ -233,10 +233,19 @@ typedef signed char RumNullCategory;
 #define RumSetPostingOffset(itup,n) ItemPointerSetBlockNumber(&(itup)->t_tid,n)
 #define RumGetPosting(itup)			((Pointer) ((char*)(itup) + RumGetPostingOffset(itup)))
 
+/*
+ * Maximum size of an item on entry tree page. Make sure that we fit at least
+ * three items on each page. (On regular B-tree indexes, we must fit at least
+ * three items: two data items and the "high key". In RUM entry tree, we don't
+ * currently store the high key explicitly, we just use the rightmost item on
+ * the page, so it would actually be enough to fit two items.)
+ */
 #define RumMaxItemSize \
-	MAXALIGN_DOWN(((BLCKSZ - SizeOfPageHeaderData - \
-		MAXALIGN(sizeof(RumPageOpaqueData))) / 6 - \
-		sizeof(RumKey) /* right bound */))
+	Min(INDEX_SIZE_MASK, \
+		MAXALIGN_DOWN(((BLCKSZ - \
+						MAXALIGN(SizeOfPageHeaderData + 3 * sizeof(ItemIdData)) - \
+						MAXALIGN(sizeof(RumPageOpaqueData))) / 3)))
+
 
 /*
  * Access macros for non-leaf entry tuples