Can't create index on text column

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Eric Jain
Your email address : Eric.Jain@isb-sib.ch

System Configuration
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Architecture (example: Intel Pentium) : Intel Pentium

Operating System (example: Linux 2.0.26 ELF) : Linux 2.4.18-19.8.0smp

PostgreSQL version (example: PostgreSQL-7.3): PostgreSQL-7.3.3

Compiler used (example: gcc 2.95.2) : gcc 3.2

Please enter a FULL description of your problem:
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Can't create index on text column containing a specific value:

ERROR: index_formtuple: data takes 8720 bytes, max is 8191

Please describe a way to repeat the problem. Please try to provide a
concise reproducible example, if at all possible:
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1)

CREATE TABLE statements (
model TEXT NOT NULL,
statement TEXT,
subject TEXT NOT NULL,
predicate TEXT NOT NULL,
object_resource TEXT,
object_string TEXT,
object_number DOUBLE PRECISION
)
WITHOUT OIDS
;

2) COPY statements FROM 'statements.tab'; /* See attachment */

3) CREATE INDEX object_string_index ON statements(object_string);

Note: Can't reproduce this error with other values, even if they are
larger. But I do not see what is special about the offending string, it
doesn't seem to contain any characters outside the range A-Z.

Interestingly, octet_length(object_string) does not produce 8720, but
8797.

If you know how this problem might be fixed, list the solution below:
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A temporary workaround may be to create an index on
"substr(object_string for 100)"...