Adjust DSM and DSA slot usage constants (back-patch).

1.  Previously, a DSA area would create up to four segments at each size
before doubling the size.  After this commit, it will create only two at
each size, so it ramps up faster and therefore needs fewer slots.

2.  Previously, the total limit on DSM slots allowed for 2 per connection.
Switch to 5 per connection.

This back-patches commit d061ea21 from release 13 into 10-12 based on a
field complaint.

Discussion: https://postgr.es/m/CAO03teA%2BjE1qt5iWDWzHqaufqBsF6EoOgZphnazps_tr_jDPZA%40mail.gmail.com
Discussion: https://postgr.es/m/CA%2BhUKGL6H2BpGbiF7Lj6QiTjTGyTLW_vLR%3DSn2tEBeTcYXiMKw%40mail.gmail.com

diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index 9bf16de940745f51a6bc725b9f6da533358b118d..40a1e46fc006936d67ae91f3c12b42737c5a04d2 100644 (file)
--- a/src/backend/storage/ipc/dsm.c
+++ b/src/backend/storage/ipc/dsm.c
@@ -45,13 +45,8 @@
 
 #define PG_DYNSHMEM_CONTROL_MAGIC      0x9a503d32
 
-/*
- * There's no point in getting too cheap here, because the minimum allocation
- * is one OS page, which is probably at least 4KB and could easily be as high
- * as 64KB.  Each currently sizeof(dsm_control_item), currently 8 bytes.
- */
 #define PG_DYNSHMEM_FIXED_SLOTS            64
-#define PG_DYNSHMEM_SLOTS_PER_BACKEND  2
+#define PG_DYNSHMEM_SLOTS_PER_BACKEND  5
 
 #define INVALID_CONTROL_SLOT       ((uint32) -1)
 

diff --git a/src/backend/utils/mmgr/dsa.c b/src/backend/utils/mmgr/dsa.c
index 900cd8357cac00dbc49736453d937654d26f3750..5a53c8290a43b027c212cd0ff974e058e55d345d 100644 (file)
--- a/src/backend/utils/mmgr/dsa.c
+++ b/src/backend/utils/mmgr/dsa.c
@@ -74,7 +74,7 @@
  * dsm.c's limits on total number of segments), or limiting the total size
  * an area can manage when using small pointers.
  */
-#define DSA_NUM_SEGMENTS_AT_EACH_SIZE 4
+#define DSA_NUM_SEGMENTS_AT_EACH_SIZE 2
 
 /*
  * The number of bits used to represent the offset part of a dsa_pointer.