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Merge with #5837
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@jcsp
Konstantin Knizhnik authored and jcsp committed Dec 5, 2023
1 parent 21c3c55 commit 66fdb54
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Showing 2 changed files with 91 additions and 73 deletions.
162 changes: 90 additions & 72 deletions pgxn/neon/libpagestore.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,7 @@ bool (*old_redo_read_buffer_filter) (XLogReaderState *record, uint8 block_id) =

static bool pageserver_flush(shardno_t shard_no);
static void pageserver_disconnect(shardno_t shard_no);
static void AssignPageserverConnstring(const char *newval, void *extra);

static shmem_startup_hook_type prev_shmem_startup_hook;
#if PG_VERSION_NUM>=150000
Expand All @@ -70,20 +71,19 @@ static shmem_request_hook_type prev_shmem_request_hook;
typedef struct
{
size_t n_shards;
size_t update_counter;
pg_atomic_uint64 begin_update_counter;
pg_atomic_uint64 end_update_counter;
char shard_connstr[MAX_SHARDS][MAX_PS_CONNSTR_LEN];
} ShardMap;


static ShardMap* shard_map;
static LWLockId shard_map_lock;
static size_t shard_map_update_counter;
static bool config_updated;
static uint64 shard_map_update_counter;

typedef struct
{
/*
* connection for each shard
* Connection for each shard
*/
PGconn *conn;
/*
Expand Down Expand Up @@ -112,9 +112,10 @@ psm_shmem_startup(void)
shard_map = (ShardMap*)ShmemInitStruct("shard_map", sizeof(ShardMap), &found);
if (!found)
{
shard_map_lock = (LWLockId)GetNamedLWLockTranche("shard_map_lock");
shard_map->n_shards = 0;
shard_map->update_counter = 1; /* force update of shared map on forst access */
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);
}
Expand All @@ -128,7 +129,6 @@ psm_shmem_request(void)
#endif

RequestAddinShmemSpace(sizeof(ShardMap));
RequestNamedLWLockTranche("shard_map_lock", 1);
}

static void
Expand All @@ -151,74 +151,41 @@ static shardno_t
load_shard_map(shardno_t shard_no, char* connstr)
{
shardno_t n_shards;
bool exclusive_lock = false;
LWLockAcquire(shard_map_lock, LW_SHARED);
uint64 begin_update_counter;
uint64 end_update_counter;

if (shard_map_update_counter != shard_map->update_counter || config_updated)
/*
* 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
{
ParseConnString:
{
char const* shard_connstr = page_server_connstring;
char const* sep;
size_t connstr_len;
int i = 0;
bool shard_map_changed = false;
do
{
sep = strchr(shard_connstr, ',');
connstr_len = sep != NULL ? sep - shard_connstr : strlen(shard_connstr);
if (connstr_len == 0)
break; /* trailing comma */
if (i >= MAX_SHARDS)
elog(ERROR, "Too many shards");
if (connstr_len >= MAX_PS_CONNSTR_LEN)
elog(ERROR, "Connection string too long");
if (i >= shard_map->n_shards ||
strcmp(shard_map->shard_connstr[i], shard_connstr) != 0)
{
if (!exclusive_lock)
{
/* Retry under exclsuive lock */
LWLockRelease(shard_map_lock);
LWLockAcquire(shard_map_lock, LW_EXCLUSIVE);
exclusive_lock = true;
goto ParseConnString;
}
shard_map_changed = true;
memcpy(shard_map->shard_connstr[i], shard_connstr, connstr_len+1);
}
shard_connstr = sep + 1;
i += 1;
} while (sep != NULL);
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 (i == 0)
elog(ERROR, "No shards were speciified");

if (shard_map_changed)
{
shard_map->update_counter += 1;
shard_map->n_shards = i;
}
}
if (shard_map_update_counter != shard_map->update_counter)
{
for (shardno_t i = 0; i < max_attached_shard_no; i++)
{
if (page_servers[i].conn)
pageserver_disconnect(i);
}
shard_map_update_counter = shard_map->update_counter;
}
config_updated = false;
}
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);
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)
strcpy(connstr, shard_map->shard_connstr[shard_no]);
if (connstr)
strncpy(connstr, shard_map->shard_connstr[shard_no], MAX_PS_CONNSTR_LEN);

LWLockRelease(shard_map_lock);
}
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++)
{
if (page_servers[i].conn)
pageserver_disconnect(i);
}
max_attached_shard_no = 0;
shard_map_update_counter = end_update_counter;
}

return n_shards;
}
Expand Down Expand Up @@ -577,7 +544,58 @@ check_neon_id(char **newval, void **extra, GucSource source)
static void
AssignPageserverConnstring(const char *newval, void *extra)
{
config_updated = true;
/*
* Load shard map only at Postmaster.
* If old page server is not available, then backends can be blocked in attempts to reconnect to it and do not reload config in this loop
*/
if (shard_map != NULL && (MyProcPid == PostmasterPid || shard_map->n_shards == 0))
{
char const* shard_connstr = newval;
char const* sep;
size_t connstr_len;
int i = 0;
bool shard_map_changed = false;
do
{
sep = strchr(shard_connstr, ',');
connstr_len = sep != NULL ? sep - shard_connstr : strlen(shard_connstr);
if (connstr_len == 0)
break; /* trailing comma */
if (i >= MAX_SHARDS)
{
elog(LOG, "Too many shards");
return;
}
if (connstr_len >= MAX_PS_CONNSTR_LEN)
{
elog(LOG, "Connection string too long");
return;
}
if (i >= shard_map->n_shards ||
strcmp(shard_map->shard_connstr[i], shard_connstr) != 0)
{
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;
i += 1;
} while (sep != NULL);

if (i == 0)
{
elog(LOG, "No shards were specified");
return;
}
if (shard_map_changed)
{
shard_map->n_shards = i;
pg_atomic_add_fetch_u64(&shard_map->end_update_counter, 1);
}
}
}

/*
Expand Down
2 changes: 1 addition & 1 deletion pgxn/neon/pagestore_smgr.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -920,7 +920,7 @@ page_server_request(void const *req)
shard_no = get_shard_number(&tag);

/*
* TODO: temporary workarround - we stream all WAL only to shard 0 so metadata and forks other than main
* TODO: temporary workarround - we stream all WAL only to shard 0, so metadata and forks other than main
* should be requested from shard 0. We still need to call get_shard_no() to check if shard map is up-to-date
*/
if (((NeonRequest *) req)->tag != T_NeonGetPageRequest || ((NeonGetPageRequest *) req)->forknum != MAIN_FORKNUM)
Expand Down

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