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outtersgouttersg
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pdo_pgsql: unbuffered fetching: test & NEWS
memory & non-regression test mention in the NEWS file
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‎NEWS

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Original file line numberDiff line numberDiff line change
@@ -40,6 +40,12 @@ PHP NEWS
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- PDO_Firebird:
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. Fixed GH-15604 (Always make input parameters nullable). (sim1984)
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- PDO_PGSQL:
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. Implement GH-15387 Pdo\Pgsql::setAttribute(PDO::ATTR_PREFETCH, 0) or
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Pdo\PgSql::prepare(…, [ PDO::ATTR_PREFETCH => 0 ]) make fetch() lazy
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instead of storing the whole result set in memory (Guillaume Outters)
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/!\ In this mode statements cannot be run parallely
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- Reflection:
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. Fixed bug GH-15718 (Segfault on ReflectionProperty::get{Hook,Hooks}() on
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dynamic properties). (DanielEScherzer)
@@ -577,7 +583,7 @@ PHP NEWS
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. Added class Pdo\Pgsql. (danack, kocsismate)
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. Retrieve the memory usage of the query result resource. (KentarouTakeda)
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. Added Pdo\Pgsql::setNoticeCallBack method to receive DB notices.
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(outtersg)
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(Guillaume Outters)
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. Added custom SQL parser. (Matteo Beccati)
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- PDO_SQLITE:

‎ext/pdo_pgsql/tests/gh15287.phpt

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@@ -0,0 +1,180 @@
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--TEST--
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PDO PgSQL #15287 (Pdo\Pgsql has no real lazy fetch mode)
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--EXTENSIONS--
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pdo
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pdo_pgsql
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--SKIPIF--
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<?php
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require __DIR__ . '/config.inc';
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require __DIR__ . '/../../../ext/pdo/tests/pdo_test.inc';
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PDOTest::skip();
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?>
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--FILE--
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<?php
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require __DIR__ . '/../../../ext/pdo/tests/pdo_test.inc';
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$pdo = PDOTest::test_factory(__DIR__ . '/common.phpt');
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$pdo->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
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// We need a dataset of several KB so that memory gain is significant.
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// See https://www.postgresql.org/message-id/1140652.1687950987%40sss.pgh.pa.us
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$pdo->exec("create temp table t (n int, t text)");
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$pdo->exec("insert into t values (0, 'original')");
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for ($i = -1; ++$i < 8;) {
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$pdo->exec("insert into t select n + 1, 'non '||t from t");
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}
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$reqOf3 = 'select 79 n union all select 80 union all select 81';
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$reqOfBig = 'select * from t';
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function display($res)
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{
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echo implode("\n", array_map(fn($row) => implode("\t", $row), $res))."\n";
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}
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echo "=== non regression ===\n";
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// libpq explicitely requires single-row-mode statements to run one at a time (one stmt must
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// be fully read, or aborted, before another one can be launched).
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// Ensure that integration does not break the ability of the traditional, prefetched mode,
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// to mix fetching of multiple statements' result.
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$stmt1 = $pdo->query($reqOf3);
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$stmt2 = $pdo->query("select * from ($reqOf3) t order by n desc");
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for ($i = -1; ++$i < 3;) {
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display([ $stmt1->fetch() ]);
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display([ $stmt2->fetch() ]);
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}
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echo "=== mem test ===\n";
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// First execute without lazy fetching, as a reference and non-regression;
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// execute twice: in case warmup reduces memory consumption, we want the stabilized consumption.
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for ($i = -1; ++$i < 5;) {
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$attrs = [];
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switch ($i) {
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case 0:
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case 3:
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echo "Without lazy fetching:\n";
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break;
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case 2:
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echo "With statement-scoped lazy fetching:\n";
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$attrs = [ PDO::ATTR_PREFETCH => 0 ];
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break;
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case 4:
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echo "With connection-scoped lazy fetching:\n";
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$pdo->setAttribute(PDO::ATTR_PREFETCH, 0);
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break;
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}
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$stmt = $pdo->prepare($reqOfBig, $attrs);
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$stmt->execute();
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$res = [];
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// No fetchAll because we want the memory of the result of the FORElast call (the last one is empty).
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while (($re = $stmt->fetch())) {
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$res[] = $re;
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// Memory introspection relies on an optionally-compiled constant.
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if (defined('PDO::PGSQL_ATTR_RESULT_MEMORY_SIZE')) {
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$mem = $stmt->getAttribute(PDO::PGSQL_ATTR_RESULT_MEMORY_SIZE);
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} else {
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// If not there emulate a return value which validates our test.
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$mem = $i < 2 ? 1 : 0;
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}
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}
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echo "ResultSet is $mem bytes long\n";
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if ($i >= 2) {
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echo "ResultSet is " . ($mem > $mem0 ? "longer" : ($mem == $mem0 ? "not shorter" : ($mem <= $mem0 / 2 ? "more than twice shorter" : "a bit shorter"))) . " than without lazy fetching\n";
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} else {
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$mem0 = $mem;
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}
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}
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$pdo->setAttribute(PDO::ATTR_PREFETCH, 0);
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foreach ([
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[ 'query', 'fetch' ],
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[ 'query', 'fetchAll' ],
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[ 'prepare', 'fetch' ],
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[ 'prepare', 'fetchAll' ],
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] as $mode) {
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echo "=== with " . implode(' / ', $mode). " ===\n";
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switch ($mode[0]) {
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case 'query':
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$stmt = $pdo->query($reqOf3);
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break;
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case 'prepare':
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$stmt = $pdo->prepare($reqOf3);
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$stmt->execute();
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break;
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}
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switch ($mode[1]) {
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case 'fetch':
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$res = [];
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while (($re = $stmt->fetch())) {
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$res[] = $re;
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}
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break;
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case 'fetchAll':
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$res = $stmt->fetchAll();
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break;
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}
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display($res);
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}
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echo "DML works too:\n";
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$pdo->exec("create temp table t2 as select 678 n, 'ok' status");
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echo "multiple calls to the same prepared statement, some interrupted before having read all results:\n";
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$stmt = $pdo->prepare("select :1 n union all select :1 + 1 union all select :1 + 2 union all select :1 + 3");
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$stmt->execute([ 32 ]);
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$res = []; for ($i = -1; ++$i < 2;) $res[] = $stmt->fetch(); display($res);
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$stmt->execute([ 15 ]);
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$res = []; while (($re = $stmt->fetch())) $res[] = $re; display($res);
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$stmt->execute([ 0 ]);
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$res = []; for ($i = -1; ++$i < 2;) $res[] = $stmt->fetch(); display($res);
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display($pdo->query("select * from t2")->fetchAll());
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?>
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--EXPECTF--
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=== non regression ===
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79
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81
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80
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80
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81
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79
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=== mem test ===
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Without lazy fetching:
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ResultSet is %d bytes long
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ResultSet is %d bytes long
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With statement-scoped lazy fetching:
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ResultSet is %d bytes long
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ResultSet is more than twice shorter than without lazy fetching
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Without lazy fetching:
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ResultSet is %d bytes long
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ResultSet is not shorter than without lazy fetching
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With connection-scoped lazy fetching:
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ResultSet is %d bytes long
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ResultSet is more than twice shorter than without lazy fetching
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=== with query / fetch ===
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79
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80
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81
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=== with query / fetchAll ===
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79
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80
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81
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=== with prepare / fetch ===
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79
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80
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81
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=== with prepare / fetchAll ===
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79
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80
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81
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DML works too:
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multiple calls to the same prepared statement, some interrupted before having read all results:
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32
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33
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15
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16
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17
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18
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0
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1
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678 ok

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