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Store stripe_size in shared memory (#12560)

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## Problem

See https://databricks.slack.com/archives/C09254R641L/p1752004515032899

stripe_size GUC update may be delayed at different backends and so cause
inconsistency with connection strings (shard map).

## Summary of changes

Postmaster should store stripe_size in shared memory as well as
connection strings.
It should be also enforced that stripe size is defined prior to
connection strings in postgresql.conf

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
Co-authored-by: Kosntantin Knizhnik <konstantin.knizhnik@databricks.com>
This commit is contained in:
Konstantin Knizhnik
2025-07-17 23:32:34 +03:00
committed by GitHub
parent 43fd5b218b
commit 7fef4435c1
2 changed files with 21 additions and 6 deletions
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20
pgxn/neon/libpagestore.c
View File

@@ -90,6 +90,7 @@ typedef struct
{
char connstring[MAX_SHARDS][MAX_PAGESERVER_CONNSTRING_SIZE];
size_t num_shards;
size_t stripe_size;
} ShardMap;
/*
@@ -110,6 +111,11 @@ typedef struct
* has changed since last access, and to detect and retry copying the value if
* the postmaster changes the value concurrently. (Postmaster doesn't have a
* PGPROC entry and therefore cannot use LWLocks.)
*
* stripe_size is now also part of ShardMap, although it is defined by separate GUC.
* Postgres doesn't provide any mechanism to enforce dependencies between GUCs,
* that it we we have to rely on order of GUC definition in config file.
* "neon.stripe_size" should be defined prior to "neon.pageserver_connstring"
*/
typedef struct
{
@@ -230,7 +236,10 @@ ParseShardMap(const char *connstr, ShardMap *result)
p = sep + 1;
}
if (result)
{
result->num_shards = nshards;
result->stripe_size = stripe_size;
}
return true;
}
@@ -291,12 +300,13 @@ AssignPageserverConnstring(const char *newval, void *extra)
* last call, terminates all existing connections to all pageservers.
*/
static void
load_shard_map(shardno_t shard_no, char *connstr_p, shardno_t *num_shards_p)
load_shard_map(shardno_t shard_no, char *connstr_p, shardno_t *num_shards_p, size_t* stripe_size_p)
{
uint64 begin_update_counter;
uint64 end_update_counter;
ShardMap *shard_map = &pagestore_shared->shard_map;
shardno_t num_shards;
size_t stripe_size;
/*
* Postmaster can update the shared memory values concurrently, in which
@@ -311,6 +321,7 @@ load_shard_map(shardno_t shard_no, char *connstr_p, shardno_t *num_shards_p)
end_update_counter = pg_atomic_read_u64(&pagestore_shared->end_update_counter);
num_shards = shard_map->num_shards;
stripe_size = shard_map->stripe_size;
if (connstr_p && shard_no < MAX_SHARDS)
strlcpy(connstr_p, shard_map->connstring[shard_no], MAX_PAGESERVER_CONNSTRING_SIZE);
pg_memory_barrier();
@@ -345,6 +356,8 @@ load_shard_map(shardno_t shard_no, char *connstr_p, shardno_t *num_shards_p)
if (num_shards_p)
*num_shards_p = num_shards;
if (stripe_size_p)
*stripe_size_p = stripe_size;
}
#define MB (1024*1024)
@@ -353,9 +366,10 @@ shardno_t
get_shard_number(BufferTag *tag)
{
shardno_t n_shards;
size_t stripe_size;
uint32 hash;
load_shard_map(0, NULL, &n_shards);
load_shard_map(0, NULL, &n_shards, &stripe_size);
#if PG_MAJORVERSION_NUM < 16
hash = murmurhash32(tag->rnode.relNode);
@@ -408,7 +422,7 @@ pageserver_connect(shardno_t shard_no, int elevel)
* Note that connstr is used both during connection start, and when we
* log the successful connection.
*/
load_shard_map(shard_no, connstr, NULL);
load_shard_map(shard_no, connstr, NULL, NULL);
switch (shard->state)
{