139 lines
4.2 KiB
Plaintext
139 lines
4.2 KiB
Plaintext
--
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-- Test large object support
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--
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-- Load a file
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CREATE TABLE lotest_stash_values (loid oid, fd integer);
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-- lo_creat(mode integer) returns oid
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-- The mode arg to lo_creat is unused, some vestigal holdover from ancient times
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-- returns the large object id
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INSERT INTO lotest_stash_values (loid) SELECT lo_creat(42);
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-- NOTE: large objects require transactions
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BEGIN;
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-- lo_open(lobjId oid, mode integer) returns integer
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-- The mode parameter to lo_open uses two constants:
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-- INV_READ = 0x20000 = 2 * 16^4
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-- INV_WRITE = 0x40000 = 4 * 16^4
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-- The return value is a file descriptor-like value which remains valid for the
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-- transaction.
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UPDATE lotest_stash_values SET fd = lo_open(loid, CAST((2 | 4) * 16^4 AS integer));
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-- loread/lowrite names are wonky, different from other functions which are lo_*
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-- lowrite(fd integer, data bytea) returns integer
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-- the integer is the number of bytes written
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SELECT lowrite(fd, '
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Whose woods these are I think I know,
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His house is in the village though.
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He will not see me stopping here,
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To watch his woods fill up with snow.
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My little horse must think it queer,
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To stop without a farmhouse near,
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Between the woods and frozen lake,
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The darkest evening of the year.
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He gives his harness bells a shake,
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To ask if there is some mistake.
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The only other sound''s the sweep,
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Of easy wind and downy flake.
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The woods are lovely, dark and deep,
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But I have promises to keep,
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And miles to go before I sleep,
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And miles to go before I sleep.
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-- Robert Frost
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') FROM lotest_stash_values;
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-- lo_close(fd integer) returns integer
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-- return value is 0 for success, or <0 for error (actually only -1, but...)
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SELECT lo_close(fd) FROM lotest_stash_values;
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END;
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-- Read out a portion
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BEGIN;
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UPDATE lotest_stash_values SET fd=lo_open(loid, CAST((2 | 4) * 16^4 AS integer));
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-- lo_lseek(fd integer, offset integer, whence integer) returns integer
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-- offset is in bytes, whence is one of three values:
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-- SEEK_SET (= 0) meaning relative to beginning
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-- SEEK_CUR (= 1) meaning relative to current position
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-- SEEK_END (= 2) meaning relative to end (offset better be negative)
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-- returns current position in file
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SELECT lo_lseek(fd, 422, 0) FROM lotest_stash_values;
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-- loread/lowrite names are wonky, different from other functions which are lo_*
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-- loread(fd integer, len integer) returns bytea
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SELECT loread(fd, 35) FROM lotest_stash_values;
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SELECT lo_lseek(fd, -19, 1) FROM lotest_stash_values;
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SELECT lowrite(fd, 'n') FROM lotest_stash_values;
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SELECT lo_tell(fd) FROM lotest_stash_values;
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SELECT lo_lseek(fd, -156, 2) FROM lotest_stash_values;
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SELECT loread(fd, 35) FROM lotest_stash_values;
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SELECT lo_close(fd) FROM lotest_stash_values;
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END;
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-- lo_unlink(lobjId oid) returns integer
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-- return value appears to always be 1
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SELECT lo_unlink(loid) from lotest_stash_values;
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TRUNCATE lotest_stash_values;
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INSERT INTO lotest_stash_values (loid) SELECT lo_import('@abs_srcdir@/data/tenk.data');
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BEGIN;
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UPDATE lotest_stash_values SET fd=lo_open(loid, CAST((2 | 4) * 16^4 AS integer));
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-- with the default BLKSZ, LOBLKSZ = 2048, so this positions us for a block
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-- edge case
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SELECT lo_lseek(fd, 2030, 0) FROM lotest_stash_values;
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-- this should get half of the value from page 0 and half from page 1 of the
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-- large object
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SELECT loread(fd, 36) FROM lotest_stash_values;
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SELECT lo_tell(fd) FROM lotest_stash_values;
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SELECT lo_lseek(fd, -26, 1) FROM lotest_stash_values;
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SELECT lowrite(fd, 'abcdefghijklmnop') FROM lotest_stash_values;
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SELECT lo_lseek(fd, 2030, 0) FROM lotest_stash_values;
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SELECT loread(fd, 36) FROM lotest_stash_values;
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SELECT lo_close(fd) FROM lotest_stash_values;
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END;
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SELECT lo_export(loid, '@abs_builddir@/results/lotest.txt') FROM lotest_stash_values;
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\lo_import 'results/lotest.txt'
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\set newloid :LASTOID
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-- just make sure \lo_export does not barf
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\lo_export :newloid 'results/lotest2.txt'
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-- This is a hack to test that export/import are reversible
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-- This uses knowledge about the inner workings of large object mechanism
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-- which should not be used outside it. This makes it a HACK
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SELECT pageno, data FROM pg_largeobject WHERE loid = (SELECT loid from lotest_stash_values)
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EXCEPT
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SELECT pageno, data FROM pg_largeobject WHERE loid = :newloid;
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SELECT lo_unlink(loid) FROM lotest_stash_values;
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\lo_unlink :newloid
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TRUNCATE lotest_stash_values;
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