digoal
2024-03-30
PostgreSQL , PolarDB , DuckDB , dsa , DSA_DEFAULT_INIT_SEGMENT_SIZE , DSA_MIN_SEGMENT_SIZE , DSA_MAX_SEGMENT_SIZE
Allow specifying initial and maximum segment sizes for DSA.
author Masahiko Sawada <msawada@postgresql.org>
Wed, 27 Mar 2024 02:43:29 +0000 (11:43 +0900)
committer Masahiko Sawada <msawada@postgresql.org>
Wed, 27 Mar 2024 02:43:29 +0000 (11:43 +0900)
commit bb952c8c8b13279eca039499249cb5dc60991603
tree ba7cc3ced86501cb0da23a66b9170ffae19dcf6c tree
parent 1f42337be535243e665f85916ce21b2d85d9f2b3 commit | diff
Allow specifying initial and maximum segment sizes for DSA.
Previously, the DSA segment size always started with 1MB and grew up
to DSA_MAX_SEGMENT_SIZE. It was inconvenient in certain scenarios,
such as when the caller desired a soft constraint on the total DSA
segment size, limiting it to less than 1MB.
This commit introduces the capability to specify the initial and
maximum DSA segment sizes when creating a DSA area, providing more
flexibility and control over memory usage.
Reviewed-by: John Naylor, Tomas Vondra
Discussion: https://postgr.es/m/CAD21AoAYGGC1ePjVX0H%2Bpp9rH%3D9vuPK19nNOiu12NprdV5TVJA%40mail.gmail.com
+/*
+ * The number of bits used to represent the offset part of a dsa_pointer.
+ * This controls the maximum size of a segment, the maximum possible
+ * allocation size and also the maximum number of segments per area.
+ */
+#if SIZEOF_DSA_POINTER == 4
+#define DSA_OFFSET_WIDTH 27 /* 32 segments of size up to 128MB */
+#else
+#define DSA_OFFSET_WIDTH 40 /* 1024 segments of size up to 1TB */
+#endif
+
+/*
+ * The default size of the initial DSM segment that backs a dsa_area created
+ * by dsa_create. After creating some number of segments of the initial size
+ * we'll double this size, and so on. Larger segments may be created if
+ * necessary to satisfy large requests.
+ */
+#define DSA_DEFAULT_INIT_SEGMENT_SIZE ((size_t) (1 * 1024 * 1024))
+
+/* The minimum size of a DSM segment. */
+#define DSA_MIN_SEGMENT_SIZE ((size_t) (256 * 1024L))
+
+/* The maximum size of a DSM segment. */
+#define DSA_MAX_SEGMENT_SIZE ((size_t) 1 << DSA_OFFSET_WIDTH)
+/* Create dsa_area with default segment sizes */
+#define dsa_create(tranch_id) \
+ dsa_create_ext(tranch_id, DSA_DEFAULT_INIT_SEGMENT_SIZE, \
+ DSA_MAX_SEGMENT_SIZE)
+
+/* Create dsa_area with default segment sizes in an existing share memory space */
+#define dsa_create_in_place(place, size, tranch_id, segment) \
+ dsa_create_in_place_ext(place, size, tranch_id, segment, \
+ DSA_DEFAULT_INIT_SEGMENT_SIZE, \
+ DSA_MAX_SEGMENT_SIZE)
+
