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Fix shard map reload synchronization

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This commit is contained in:
Konstantin Knizhnik
2023-12-01 21:13:09 +02:00
parent 864d5f84e9
commit 86c76d4b59
1 changed files with 36 additions and 24 deletions
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60
pgxn/neon/libpagestore.c
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@@ -71,7 +71,8 @@ static shmem_request_hook_type prev_shmem_request_hook;
typedef struct
{
size_t n_shards;
pg_atomic_uint64 update_counter;
pg_atomic_uint64 begin_update_counter;
pg_atomic_uint64 end_update_counter;
char shard_connstr[MAX_SHARDS][MAX_PS_CONNSTR_LEN];
} ShardMap;
@@ -112,7 +113,8 @@ psm_shmem_startup(void)
if (!found)
{
shard_map->n_shards = 0;
pg_atomic_init_u64(&shard_map->update_counter, 0);
pg_atomic_init_u64(&shard_map->begin_update_counter, 0);
pg_atomic_init_u64(&shard_map->end_update_counter, 0);
AssignPageserverConnstring(page_server_connstring, NULL);
}
LWLockRelease(AddinShmemInitLock);
@@ -149,9 +151,32 @@ static shardno_t
load_shard_map(shardno_t shard_no, char* connstr)
{
shardno_t n_shards;
uint64 update_counter = pg_atomic_read_u64(&shard_map->update_counter);
uint64 begin_update_counter;
uint64 end_update_counter;
if (shard_map_update_counter != update_counter)
/*
* There is race condition here between backendc and postmaster which can update shard map.
* We recheck update couner after copying connection string to check that configuration was not changed.
*/
do
{
begin_update_counter = pg_atomic_read_u64(&shard_map->begin_update_counter);
end_update_counter = pg_atomic_read_u64(&shard_map->end_update_counter);
n_shards = shard_map->n_shards;
if (shard_no >= n_shards)
elog(ERROR, "Shard %d is greater or equal than number of shards %d", shard_no, n_shards);
if (connstr)
strncpy(connstr, shard_map->shard_connstr[shard_no], MAX_PS_CONNSTR_LEN);
}
while (begin_update_counter != end_update_counter
|| begin_update_counter != pg_atomic_read_u64(&shard_map->begin_update_counter)
|| end_update_counter != pg_atomic_read_u64(&shard_map->end_update_counter));
if (shard_map_update_counter != end_update_counter)
{
/* Reset all connections if connection strings are changed */
for (shardno_t i = 0; i < max_attached_shard_no; i++)
@@ -160,26 +185,9 @@ load_shard_map(shardno_t shard_no, char* connstr)
pageserver_disconnect(i);
}
max_attached_shard_no = 0;
shard_map_update_counter = end_update_counter;
}
/*
* There is race condition here between backendc and postmaster which can update shard map.
* We recheck update couner after copying connection string to check that configuration was not changed.
*/
do
{
shard_map_update_counter = update_counter;
n_shards = shard_map->n_shards;
if (shard_no >= n_shards)
elog(ERROR, "Shard %d is greater or equal than number of shards %d", shard_no, n_shards);
if (connstr)
strncpy(connstr, shard_map->shard_connstr[shard_no], MAX_PS_CONNSTR_LEN);
update_counter = pg_atomic_read_u64(&shard_map->update_counter);
}
while (update_counter != shard_map_update_counter);
return n_shards;
}
@@ -575,7 +583,11 @@ AssignPageserverConnstring(const char *newval, void *extra)
if (i >= shard_map->n_shards ||
strcmp(shard_map->shard_connstr[i], shard_connstr) != 0)
{
shard_map_changed = true;
if (!shard_map_changed)
{
pg_atomic_add_fetch_u64(&shard_map->begin_update_counter, 1);
shard_map_changed = true;
}
memcpy(shard_map->shard_connstr[i], shard_connstr, connstr_len+1);
}
shard_connstr = sep + 1;
@@ -590,7 +602,7 @@ AssignPageserverConnstring(const char *newval, void *extra)
if (shard_map_changed)
{
shard_map->n_shards = i;
pg_atomic_add_fetch_u64(&shard_map->update_counter, 1);
pg_atomic_add_fetch_u64(&shard_map->end_update_counter, 1);
}
}
}