postgres.git / summary / log / commit / refs

commit    f5332503ef0a65b90366c2a222e1b5aa64977a95
Author:   Thomas Munro <tmunro@postgresql.org>
Date:     Thu Nov 19 21:44:09 2020 +0000
First released in: 10.16, 11.11, 12.6

    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


 src/backend/storage/ipc/dsm.c | 7 +------
 src/backend/utils/mmgr/dsa.c  | 2 +-
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/src/backend/storage/ipc/dsm.c b/src/backend/storage/ipc/dsm.c
index a5e11187dcf..6d5eefb1d94 100644
--- 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 e09cae9b612..6ae13687568 100644
--- 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.


[parent: 513db7b7004c]