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ext/pgsql: adding pg_result_memory_size. #14214

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ext/pgsql: adding pg_result_memory_size. #14214

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1 change: 1 addition & 0 deletions UPGRADING
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Original file line number Diff line number Diff line change
Expand Up @@ -339,6 +339,7 @@ PHP 8.4 UPGRADE NOTES
3-parameter signature with a null $row parameter instead.
. Calling pg_field_is_null() with 2 arguments is deprecated. Use the
3-parameter signature with a null $row parameter instead.
. Added pg_result_memory_size to get the visibility the memory used by a query result.

- Reflection:
. Calling ReflectionMethod::__construct() with 1 argument is deprecated.
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1 change: 1 addition & 0 deletions ext/pgsql/config.m4
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Expand Up @@ -66,6 +66,7 @@ if test "$PHP_PGSQL" != "no"; then
AC_CHECK_LIB(pq, pg_encoding_to_char,AC_DEFINE(HAVE_PGSQL_WITH_MULTIBYTE_SUPPORT,1,[Whether libpq is compiled with --enable-multibyte]))
AC_CHECK_LIB(pq, lo_truncate64, AC_DEFINE(HAVE_PG_LO64,1,[PostgreSQL 9.3 or later]))
AC_CHECK_LIB(pq, PQsetErrorContextVisibility, AC_DEFINE(HAVE_PG_CONTEXT_VISIBILITY,1,[PostgreSQL 9.6 or later]))
AC_CHECK_LIB(pq, PQresultMemorySize, AC_DEFINE(HAVE_PG_RESULT_MEMORY_SIZE,1,[PostgreSQL 12 or later]))
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NOTE:
PostgreSQL: Documentation: 12: E.20. Release 12
https://www.postgresql.org/docs/12/release-12.html#id-1.11.6.24.5.9

E.20.3.7. Client Interfaces

  • Add libpq function PQresultMemorySize() to report the memory used by a query result (Lars Kanis, Tom Lane)

LIBS=$old_LIBS
LDFLAGS=$old_LDFLAGS

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17 changes: 17 additions & 0 deletions ext/pgsql/pgsql.c
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Expand Up @@ -2911,6 +2911,23 @@ PHP_FUNCTION(pg_set_error_context_visibility)
}
#endif

#ifdef HAVE_PG_RESULT_MEMORY_SIZE
PHP_FUNCTION(pg_result_memory_size)
{
zval *result;
pgsql_result_handle *pg_result;

if (zend_parse_parameters(ZEND_NUM_ARGS(), "O", &result, pgsql_result_ce) == FAILURE) {
RETURN_THROWS();
}

pg_result = Z_PGSQL_RESULT_P(result);
CHECK_PGSQL_RESULT(pg_result);

RETURN_LONG(PQresultMemorySize(pg_result->result));
}
#endif

/* {{{ Set client encoding */
PHP_FUNCTION(pg_set_client_encoding)
{
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4 changes: 4 additions & 0 deletions ext/pgsql/pgsql.stub.php
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Expand Up @@ -943,6 +943,10 @@ function pg_select(PgSql\Connection $connection, string $table_name, array $cond
#ifdef HAVE_PG_CONTEXT_VISIBILITY
function pg_set_error_context_visibility(PgSql\Connection $connection, int $visibility): int {}
#endif

#ifdef HAVE_PG_RESULT_MEMORY_SIZE
function pg_result_memory_size(PgSql\Result $result): int {}
#endif
}

namespace PgSql {
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14 changes: 13 additions & 1 deletion ext/pgsql/pgsql_arginfo.h
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29 changes: 29 additions & 0 deletions ext/pgsql/tests/pg_result_memory_size.phpt
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@@ -0,0 +1,29 @@
--TEST--
pg_result_memory_size
--EXTENSIONS--
pgsql
--SKIPIF--
<?php
include("inc/skipif.inc");
if (!function_exists('pg_result_memory_size')) die('skip function pg_result_memory_size() does not exist');
?>
--FILE--
<?php
include('inc/config.inc');

$db = pg_connect($conn_str);

$result = pg_query($db, 'select 1');
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question: is the memory usage deterministic right ? If that s the case if I redo this query it should be the same amount correct ?

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The memory usage returned by PQresultMemorySize() for the same query is generally consistent, but this cannot be guaranteed in all cases due to several factors:

  • Version of libpq: Although significant differences are unlikely, the lack of documented specifications of libpq means we cannot ensure identical behavior across all versions.
  • CPU architecture: Differences in architecture could potentially influence memory usage.
  • Query purity: Non-deterministic elements, such as the output of VOLATILE functions or results from INSERT INTO .. RETURNING ... / UPDATE ... RETURNING, can affect the memory used.

Based on some tests with simple queries, the memory usage has been consistent when none of these variables are at play. However, I must note that I am not deeply familiar with the internal implementation of libpq, so while my response is based on research and tests, it might not cover all possible scenarios.

(For the above reasons, I did not write the output size directly in the test, but instead tested by comparing the two results)

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@devnexen devnexen May 13, 2024 •
edited
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Thanks for the detail but what I meant if within your test if I do

$result = pg_query($db, 'select 1');
$size_3 = pg_result_memory_size($result);
var_dump($size_1 == $size_3);

it should be true then ?

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Yes, true in that case.
(Although not guaranteed, I don't think this behavior will change.)

$size_1 = pg_result_memory_size($result);

$result = pg_query($db, "select generate_series(1, 10000) as i, repeat('string', 100)");
$size_2 = pg_result_memory_size($result);

var_dump($size_1);
var_dump($size_2);
var_dump($size_1 < $size_2);
?>
--EXPECTF--
int(%d)
int(%d)
bool(true)
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