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postgresql/contrib/postgres_fdw/connection.c

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/*-------------------------------------------------------------------------
*
* connection.c
* Connection management functions for postgres_fdw
*
* Portions Copyright (c) 2012-2019, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/postgres_fdw/connection.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_user_mapping.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postgres_fdw.h"
#include "storage/latch.h"
#include "utils/hsearch.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/syscache.h"
/*
* Connection cache hash table entry
*
* The lookup key in this hash table is the user mapping OID. We use just one
* connection per user mapping ID, which ensures that all the scans use the
* same snapshot during a query. Using the user mapping OID rather than
* the foreign server OID + user OID avoids creating multiple connections when
* the public user mapping applies to all user OIDs.
*
* The "conn" pointer can be NULL if we don't currently have a live connection.
* When we do have a connection, xact_depth tracks the current depth of
* transactions and subtransactions open on the remote side. We need to issue
* commands at the same nesting depth on the remote as we're executing at
* ourselves, so that rolling back a subtransaction will kill the right
* queries and not the wrong ones.
*/
typedef Oid ConnCacheKey;
typedef struct ConnCacheEntry
{
ConnCacheKey key; /* hash key (must be first) */
PGconn *conn; /* connection to foreign server, or NULL */
/* Remaining fields are invalid when conn is NULL: */
int xact_depth; /* 0 = no xact open, 1 = main xact open, 2 =
* one level of subxact open, etc */
bool have_prep_stmt; /* have we prepared any stmts in this xact? */
bool have_error; /* have any subxacts aborted in this xact? */
bool changing_xact_state; /* xact state change in process */
bool invalidated; /* true if reconnect is pending */
uint32 server_hashvalue; /* hash value of foreign server OID */
uint32 mapping_hashvalue; /* hash value of user mapping OID */
} ConnCacheEntry;
/*
* Connection cache (initialized on first use)
*/
static HTAB *ConnectionHash = NULL;
/* for assigning cursor numbers and prepared statement numbers */
static unsigned int cursor_number = 0;
static unsigned int prep_stmt_number = 0;
/* tracks whether any work is needed in callback functions */
static bool xact_got_connection = false;
/* prototypes of private functions */
static PGconn *connect_pg_server(ForeignServer *server, UserMapping *user);
static void disconnect_pg_server(ConnCacheEntry *entry);
static void check_conn_params(const char **keywords, const char **values, UserMapping *user);
static void configure_remote_session(PGconn *conn);
static void do_sql_command(PGconn *conn, const char *sql);
static void begin_remote_xact(ConnCacheEntry *entry);
static void pgfdw_xact_callback(XactEvent event, void *arg);
static void pgfdw_subxact_callback(SubXactEvent event,
SubTransactionId mySubid,
SubTransactionId parentSubid,
void *arg);
static void pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue);
static void pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry);
static bool pgfdw_cancel_query(PGconn *conn);
static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query,
bool ignore_errors);
static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime,
PGresult **result);
/*
* Get a PGconn which can be used to execute queries on the remote PostgreSQL
* server with the user's authorization. A new connection is established
* if we don't already have a suitable one, and a transaction is opened at
* the right subtransaction nesting depth if we didn't do that already.
*
* will_prep_stmt must be true if caller intends to create any prepared
* statements. Since those don't go away automatically at transaction end
* (not even on error), we need this flag to cue manual cleanup.
*/
PGconn *
GetConnection(UserMapping *user, bool will_prep_stmt)
{
bool found;
ConnCacheEntry *entry;
ConnCacheKey key;
/* First time through, initialize connection cache hashtable */
if (ConnectionHash == NULL)
{
HASHCTL ctl;
MemSet(&ctl, 0, sizeof(ctl));
ctl.keysize = sizeof(ConnCacheKey);
ctl.entrysize = sizeof(ConnCacheEntry);
/* allocate ConnectionHash in the cache context */
ctl.hcxt = CacheMemoryContext;
ConnectionHash = hash_create("postgres_fdw connections", 8,
&ctl,
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
/*
* Register some callback functions that manage connection cleanup.
* This should be done just once in each backend.
*/
RegisterXactCallback(pgfdw_xact_callback, NULL);
RegisterSubXactCallback(pgfdw_subxact_callback, NULL);
CacheRegisterSyscacheCallback(FOREIGNSERVEROID,
pgfdw_inval_callback, (Datum) 0);
CacheRegisterSyscacheCallback(USERMAPPINGOID,
pgfdw_inval_callback, (Datum) 0);
}
/* Set flag that we did GetConnection during the current transaction */
xact_got_connection = true;
/* Create hash key for the entry. Assume no pad bytes in key struct */
key = user->umid;
/*
* Find or create cached entry for requested connection.
*/
entry = hash_search(ConnectionHash, &key, HASH_ENTER, &found);
if (!found)
{
/*
* We need only clear "conn" here; remaining fields will be filled
* later when "conn" is set.
*/
entry->conn = NULL;
}
/* Reject further use of connections which failed abort cleanup. */
pgfdw_reject_incomplete_xact_state_change(entry);
/*
* If the connection needs to be remade due to invalidation, disconnect as
* soon as we're out of all transactions.
*/
if (entry->conn != NULL && entry->invalidated && entry->xact_depth == 0)
{
elog(DEBUG3, "closing connection %p for option changes to take effect",
entry->conn);
disconnect_pg_server(entry);
}
/*
* We don't check the health of cached connection here, because it would
* require some overhead. Broken connection will be detected when the
* connection is actually used.
*/
/*
* If cache entry doesn't have a connection, we have to establish a new
* connection. (If connect_pg_server throws an error, the cache entry
* will remain in a valid empty state, ie conn == NULL.)
*/
if (entry->conn == NULL)
{
ForeignServer *server = GetForeignServer(user->serverid);
/* Reset all transient state fields, to be sure all are clean */
entry->xact_depth = 0;
entry->have_prep_stmt = false;
entry->have_error = false;
entry->changing_xact_state = false;
entry->invalidated = false;
entry->server_hashvalue =
GetSysCacheHashValue1(FOREIGNSERVEROID,
ObjectIdGetDatum(server->serverid));
entry->mapping_hashvalue =
GetSysCacheHashValue1(USERMAPPINGOID,
ObjectIdGetDatum(user->umid));
/* Now try to make the connection */
entry->conn = connect_pg_server(server, user);
elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\" (user mapping oid %u, userid %u)",
entry->conn, server->servername, user->umid, user->userid);
}
/*
* Start a new transaction or subtransaction if needed.
*/
begin_remote_xact(entry);
/* Remember if caller will prepare statements */
entry->have_prep_stmt |= will_prep_stmt;
return entry->conn;
}
/*
* Connect to remote server using specified server and user mapping properties.
*/
static PGconn *
connect_pg_server(ForeignServer *server, UserMapping *user)
{
PGconn *volatile conn = NULL;
/*
* Use PG_TRY block to ensure closing connection on error.
*/
PG_TRY();
{
const char **keywords;
const char **values;
int n;
/*
* Construct connection params from generic options of ForeignServer
* and UserMapping. (Some of them might not be libpq options, in
* which case we'll just waste a few array slots.) Add 3 extra slots
* for fallback_application_name, client_encoding, end marker.
*/
n = list_length(server->options) + list_length(user->options) + 3;
keywords = (const char **) palloc(n * sizeof(char *));
values = (const char **) palloc(n * sizeof(char *));
n = 0;
n += ExtractConnectionOptions(server->options,
keywords + n, values + n);
n += ExtractConnectionOptions(user->options,
keywords + n, values + n);
/* Use "postgres_fdw" as fallback_application_name. */
keywords[n] = "fallback_application_name";
values[n] = "postgres_fdw";
n++;
/* Set client_encoding so that libpq can convert encoding properly. */
keywords[n] = "client_encoding";
values[n] = GetDatabaseEncodingName();
n++;
keywords[n] = values[n] = NULL;
/* verify connection parameters and make connection */
check_conn_params(keywords, values, user);
conn = PQconnectdbParams(keywords, values, false);
if (!conn || PQstatus(conn) != CONNECTION_OK)
ereport(ERROR,
(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
errmsg("could not connect to server \"%s\"",
server->servername),
errdetail_internal("%s", pchomp(PQerrorMessage(conn)))));
/*
* Check that non-superuser has used password to establish connection;
* otherwise, he's piggybacking on the postgres server's user
* identity. See also dblink_security_check() in contrib/dblink.
*/
if (!superuser_arg(user->userid) && !PQconnectionUsedPassword(conn))
ereport(ERROR,
(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
errmsg("password is required"),
errdetail("Non-superuser cannot connect if the server does not request a password."),
errhint("Target server's authentication method must be changed.")));
/* Prepare new session for use */
configure_remote_session(conn);
pfree(keywords);
pfree(values);
}
PG_CATCH();
{
/* Release PGconn data structure if we managed to create one */
if (conn)
PQfinish(conn);
PG_RE_THROW();
}
PG_END_TRY();
return conn;
}
/*
* Disconnect any open connection for a connection cache entry.
*/
static void
disconnect_pg_server(ConnCacheEntry *entry)
{
if (entry->conn != NULL)
{
PQfinish(entry->conn);
entry->conn = NULL;
}
}
/*
* For non-superusers, insist that the connstr specify a password. This
* prevents a password from being picked up from .pgpass, a service file,
* the environment, etc. We don't want the postgres user's passwords
* to be accessible to non-superusers. (See also dblink_connstr_check in
* contrib/dblink.)
*/
static void
check_conn_params(const char **keywords, const char **values, UserMapping *user)
{
int i;
/* no check required if superuser */
if (superuser_arg(user->userid))
return;
/* ok if params contain a non-empty password */
for (i = 0; keywords[i] != NULL; i++)
{
if (strcmp(keywords[i], "password") == 0 && values[i][0] != '\0')
return;
}
ereport(ERROR,
(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
errmsg("password is required"),
errdetail("Non-superusers must provide a password in the user mapping.")));
}
/*
* Issue SET commands to make sure remote session is configured properly.
*
* We do this just once at connection, assuming nothing will change the
* values later. Since we'll never send volatile function calls to the
* remote, there shouldn't be any way to break this assumption from our end.
* It's possible to think of ways to break it at the remote end, eg making
* a foreign table point to a view that includes a set_config call ---
* but once you admit the possibility of a malicious view definition,
* there are any number of ways to break things.
*/
static void
configure_remote_session(PGconn *conn)
{
int remoteversion = PQserverVersion(conn);
/* Force the search path to contain only pg_catalog (see deparse.c) */
do_sql_command(conn, "SET search_path = pg_catalog");
/*
* Set remote timezone; this is basically just cosmetic, since all
* transmitted and returned timestamptzs should specify a zone explicitly
* anyway. However it makes the regression test outputs more predictable.
*
* We don't risk setting remote zone equal to ours, since the remote
* server might use a different timezone database. Instead, use UTC
* (quoted, because very old servers are picky about case).
*/
do_sql_command(conn, "SET timezone = 'UTC'");
/*
* Set values needed to ensure unambiguous data output from remote. (This
* logic should match what pg_dump does. See also set_transmission_modes
* in postgres_fdw.c.)
*/
do_sql_command(conn, "SET datestyle = ISO");
if (remoteversion >= 80400)
do_sql_command(conn, "SET intervalstyle = postgres");
if (remoteversion >= 90000)
do_sql_command(conn, "SET extra_float_digits = 3");
else
do_sql_command(conn, "SET extra_float_digits = 2");
}
/*
* Convenience subroutine to issue a non-data-returning SQL command to remote
*/
static void
do_sql_command(PGconn *conn, const char *sql)
{
PGresult *res;
if (!PQsendQuery(conn, sql))
pgfdw_report_error(ERROR, NULL, conn, false, sql);
res = pgfdw_get_result(conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, conn, true, sql);
PQclear(res);
}
/*
* Start remote transaction or subtransaction, if needed.
*
* Note that we always use at least REPEATABLE READ in the remote session.
* This is so that, if a query initiates multiple scans of the same or
* different foreign tables, we will get snapshot-consistent results from
* those scans. A disadvantage is that we can't provide sane emulation of
* READ COMMITTED behavior --- it would be nice if we had some other way to
* control which remote queries share a snapshot.
*/
static void
begin_remote_xact(ConnCacheEntry *entry)
{
int curlevel = GetCurrentTransactionNestLevel();
/* Start main transaction if we haven't yet */
if (entry->xact_depth <= 0)
{
const char *sql;
elog(DEBUG3, "starting remote transaction on connection %p",
entry->conn);
if (IsolationIsSerializable())
sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE";
else
sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ";
entry->changing_xact_state = true;
do_sql_command(entry->conn, sql);
entry->xact_depth = 1;
entry->changing_xact_state = false;
}
/*
* If we're in a subtransaction, stack up savepoints to match our level.
* This ensures we can rollback just the desired effects when a
* subtransaction aborts.
*/
while (entry->xact_depth < curlevel)
{
char sql[64];
snprintf(sql, sizeof(sql), "SAVEPOINT s%d", entry->xact_depth + 1);
entry->changing_xact_state = true;
do_sql_command(entry->conn, sql);
entry->xact_depth++;
entry->changing_xact_state = false;
}
}
/*
* Release connection reference count created by calling GetConnection.
*/
void
ReleaseConnection(PGconn *conn)
{
/*
* Currently, we don't actually track connection references because all
* cleanup is managed on a transaction or subtransaction basis instead. So
* there's nothing to do here.
*/
}
/*
* Assign a "unique" number for a cursor.
*
* These really only need to be unique per connection within a transaction.
* For the moment we ignore the per-connection point and assign them across
* all connections in the transaction, but we ask for the connection to be
* supplied in case we want to refine that.
*
* Note that even if wraparound happens in a very long transaction, actual
* collisions are highly improbable; just be sure to use %u not %d to print.
*/
unsigned int
GetCursorNumber(PGconn *conn)
{
return ++cursor_number;
}
/*
* Assign a "unique" number for a prepared statement.
*
* This works much like GetCursorNumber, except that we never reset the counter
* within a session. That's because we can't be 100% sure we've gotten rid
* of all prepared statements on all connections, and it's not really worth
* increasing the risk of prepared-statement name collisions by resetting.
*/
unsigned int
GetPrepStmtNumber(PGconn *conn)
{
return ++prep_stmt_number;
}
/*
* Submit a query and wait for the result.
*
* This function is interruptible by signals.
*
* Caller is responsible for the error handling on the result.
*/
PGresult *
pgfdw_exec_query(PGconn *conn, const char *query)
{
/*
* Submit a query. Since we don't use non-blocking mode, this also can
* block. But its risk is relatively small, so we ignore that for now.
*/
if (!PQsendQuery(conn, query))
pgfdw_report_error(ERROR, NULL, conn, false, query);
/* Wait for the result. */
return pgfdw_get_result(conn, query);
}
/*
* Wait for the result from a prior asynchronous execution function call.
*
* This function offers quick responsiveness by checking for any interruptions.
*
* This function emulates PQexec()'s behavior of returning the last result
* when there are many.
*
* Caller is responsible for the error handling on the result.
*/
PGresult *
pgfdw_get_result(PGconn *conn, const char *query)
{
PGresult *volatile last_res = NULL;
/* In what follows, do not leak any PGresults on an error. */
PG_TRY();
{
for (;;)
{
PGresult *res;
while (PQisBusy(conn))
{
int wc;
/* Sleep until there's something to do */
wc = WaitLatchOrSocket(MyLatch,
WL_LATCH_SET | WL_SOCKET_READABLE |
WL_EXIT_ON_PM_DEATH,
PQsocket(conn),
-1L, PG_WAIT_EXTENSION);
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
/* Data available in socket? */
if (wc & WL_SOCKET_READABLE)
{
if (!PQconsumeInput(conn))
pgfdw_report_error(ERROR, NULL, conn, false, query);
}
}
res = PQgetResult(conn);
if (res == NULL)
break; /* query is complete */
PQclear(last_res);
last_res = res;
}
}
PG_CATCH();
{
PQclear(last_res);
PG_RE_THROW();
}
PG_END_TRY();
return last_res;
}
/*
* Report an error we got from the remote server.
*
* elevel: error level to use (typically ERROR, but might be less)
* res: PGresult containing the error
* conn: connection we did the query on
* clear: if true, PQclear the result (otherwise caller will handle it)
* sql: NULL, or text of remote command we tried to execute
*
* Note: callers that choose not to throw ERROR for a remote error are
* responsible for making sure that the associated ConnCacheEntry gets
* marked with have_error = true.
*/
void
pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
bool clear, const char *sql)
{
/* If requested, PGresult must be released before leaving this function. */
PG_TRY();
{
char *diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
char *message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
char *message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
char *message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
char *message_context = PQresultErrorField(res, PG_DIAG_CONTEXT);
int sqlstate;
if (diag_sqlstate)
sqlstate = MAKE_SQLSTATE(diag_sqlstate[0],
diag_sqlstate[1],
diag_sqlstate[2],
diag_sqlstate[3],
diag_sqlstate[4]);
else
sqlstate = ERRCODE_CONNECTION_FAILURE;
/*
* If we don't get a message from the PGresult, try the PGconn. This
* is needed because for connection-level failures, PQexec may just
* return NULL, not a PGresult at all.
*/
if (message_primary == NULL)
message_primary = pchomp(PQerrorMessage(conn));
ereport(elevel,
(errcode(sqlstate),
message_primary ? errmsg_internal("%s", message_primary) :
errmsg("could not obtain message string for remote error"),
message_detail ? errdetail_internal("%s", message_detail) : 0,
message_hint ? errhint("%s", message_hint) : 0,
message_context ? errcontext("%s", message_context) : 0,
sql ? errcontext("remote SQL command: %s", sql) : 0));
}
PG_CATCH();
{
if (clear)
PQclear(res);
PG_RE_THROW();
}
PG_END_TRY();
if (clear)
PQclear(res);
}
/*
* pgfdw_xact_callback --- cleanup at main-transaction end.
*/
static void
pgfdw_xact_callback(XactEvent event, void *arg)
{
HASH_SEQ_STATUS scan;
ConnCacheEntry *entry;
/* Quick exit if no connections were touched in this transaction. */
if (!xact_got_connection)
return;
/*
* Scan all connection cache entries to find open remote transactions, and
* close them.
*/
hash_seq_init(&scan, ConnectionHash);
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
{
PGresult *res;
/* Ignore cache entry if no open connection right now */
if (entry->conn == NULL)
continue;
/* If it has an open remote transaction, try to close it */
if (entry->xact_depth > 0)
{
bool abort_cleanup_failure = false;
elog(DEBUG3, "closing remote transaction on connection %p",
entry->conn);
switch (event)
{
case XACT_EVENT_PARALLEL_PRE_COMMIT:
case XACT_EVENT_PRE_COMMIT:
/*
* If abort cleanup previously failed for this connection,
* we can't issue any more commands against it.
*/
pgfdw_reject_incomplete_xact_state_change(entry);
/* Commit all remote transactions during pre-commit */
entry->changing_xact_state = true;
do_sql_command(entry->conn, "COMMIT TRANSACTION");
entry->changing_xact_state = false;
/*
* If there were any errors in subtransactions, and we
* made prepared statements, do a DEALLOCATE ALL to make
* sure we get rid of all prepared statements. This is
* annoying and not terribly bulletproof, but it's
* probably not worth trying harder.
*
* DEALLOCATE ALL only exists in 8.3 and later, so this
* constrains how old a server postgres_fdw can
* communicate with. We intentionally ignore errors in
* the DEALLOCATE, so that we can hobble along to some
* extent with older servers (leaking prepared statements
* as we go; but we don't really support update operations
* pre-8.3 anyway).
*/
if (entry->have_prep_stmt && entry->have_error)
{
res = PQexec(entry->conn, "DEALLOCATE ALL");
PQclear(res);
}
entry->have_prep_stmt = false;
entry->have_error = false;
break;
case XACT_EVENT_PRE_PREPARE:
/*
* We disallow remote transactions that modified anything,
* since it's not very reasonable to hold them open until
* the prepared transaction is committed. For the moment,
* throw error unconditionally; later we might allow
* read-only cases. Note that the error will cause us to
* come right back here with event == XACT_EVENT_ABORT, so
* we'll clean up the connection state at that point.
*/
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot prepare a transaction that modified remote tables")));
break;
case XACT_EVENT_PARALLEL_COMMIT:
case XACT_EVENT_COMMIT:
case XACT_EVENT_PREPARE:
/* Pre-commit should have closed the open transaction */
elog(ERROR, "missed cleaning up connection during pre-commit");
break;
case XACT_EVENT_PARALLEL_ABORT:
case XACT_EVENT_ABORT:
/*
* Don't try to clean up the connection if we're already
* in error recursion trouble.
*/
if (in_error_recursion_trouble())
entry->changing_xact_state = true;
/*
* If connection is already unsalvageable, don't touch it
* further.
*/
if (entry->changing_xact_state)
break;
/*
* Mark this connection as in the process of changing
* transaction state.
*/
entry->changing_xact_state = true;
/* Assume we might have lost track of prepared statements */
entry->have_error = true;
/*
* If a command has been submitted to the remote server by
* using an asynchronous execution function, the command
* might not have yet completed. Check to see if a
* command is still being processed by the remote server,
* and if so, request cancellation of the command.
*/
if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE &&
!pgfdw_cancel_query(entry->conn))
{
/* Unable to cancel running query. */
abort_cleanup_failure = true;
}
else if (!pgfdw_exec_cleanup_query(entry->conn,
"ABORT TRANSACTION",
false))
{
/* Unable to abort remote transaction. */
abort_cleanup_failure = true;
}
else if (entry->have_prep_stmt && entry->have_error &&
!pgfdw_exec_cleanup_query(entry->conn,
"DEALLOCATE ALL",
true))
{
/* Trouble clearing prepared statements. */
abort_cleanup_failure = true;
}
else
{
entry->have_prep_stmt = false;
entry->have_error = false;
}
/* Disarm changing_xact_state if it all worked. */
entry->changing_xact_state = abort_cleanup_failure;
break;
}
}
/* Reset state to show we're out of a transaction */
entry->xact_depth = 0;
/*
* If the connection isn't in a good idle state, discard it to
* recover. Next GetConnection will open a new connection.
*/
if (PQstatus(entry->conn) != CONNECTION_OK ||
PQtransactionStatus(entry->conn) != PQTRANS_IDLE ||
entry->changing_xact_state)
{
elog(DEBUG3, "discarding connection %p", entry->conn);
disconnect_pg_server(entry);
}
}
/*
* Regardless of the event type, we can now mark ourselves as out of the
* transaction. (Note: if we are here during PRE_COMMIT or PRE_PREPARE,
* this saves a useless scan of the hashtable during COMMIT or PREPARE.)
*/
xact_got_connection = false;
/* Also reset cursor numbering for next transaction */
cursor_number = 0;
}
/*
* pgfdw_subxact_callback --- cleanup at subtransaction end.
*/
static void
pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
SubTransactionId parentSubid, void *arg)
{
HASH_SEQ_STATUS scan;
ConnCacheEntry *entry;
int curlevel;
/* Nothing to do at subxact start, nor after commit. */
if (!(event == SUBXACT_EVENT_PRE_COMMIT_SUB ||
event == SUBXACT_EVENT_ABORT_SUB))
return;
/* Quick exit if no connections were touched in this transaction. */
if (!xact_got_connection)
return;
/*
* Scan all connection cache entries to find open remote subtransactions
* of the current level, and close them.
*/
curlevel = GetCurrentTransactionNestLevel();
hash_seq_init(&scan, ConnectionHash);
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
{
char sql[100];
/*
* We only care about connections with open remote subtransactions of
* the current level.
*/
if (entry->conn == NULL || entry->xact_depth < curlevel)
continue;
if (entry->xact_depth > curlevel)
elog(ERROR, "missed cleaning up remote subtransaction at level %d",
entry->xact_depth);
if (event == SUBXACT_EVENT_PRE_COMMIT_SUB)
{
/*
* If abort cleanup previously failed for this connection, we
* can't issue any more commands against it.
*/
pgfdw_reject_incomplete_xact_state_change(entry);
/* Commit all remote subtransactions during pre-commit */
snprintf(sql, sizeof(sql), "RELEASE SAVEPOINT s%d", curlevel);
entry->changing_xact_state = true;
do_sql_command(entry->conn, sql);
entry->changing_xact_state = false;
}
else if (in_error_recursion_trouble())
{
/*
* Don't try to clean up the connection if we're already in error
* recursion trouble.
*/
entry->changing_xact_state = true;
}
else if (!entry->changing_xact_state)
{
bool abort_cleanup_failure = false;
/* Remember that abort cleanup is in progress. */
entry->changing_xact_state = true;
/* Assume we might have lost track of prepared statements */
entry->have_error = true;
/*
* If a command has been submitted to the remote server by using
* an asynchronous execution function, the command might not have
* yet completed. Check to see if a command is still being
* processed by the remote server, and if so, request cancellation
* of the command.
*/
if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE &&
!pgfdw_cancel_query(entry->conn))
abort_cleanup_failure = true;
else
{
/* Rollback all remote subtransactions during abort */
snprintf(sql, sizeof(sql),
"ROLLBACK TO SAVEPOINT s%d; RELEASE SAVEPOINT s%d",
curlevel, curlevel);
if (!pgfdw_exec_cleanup_query(entry->conn, sql, false))
abort_cleanup_failure = true;
}
/* Disarm changing_xact_state if it all worked. */
entry->changing_xact_state = abort_cleanup_failure;
}
/* OK, we're outta that level of subtransaction */
entry->xact_depth--;
}
}
/*
* Connection invalidation callback function
*
* After a change to a pg_foreign_server or pg_user_mapping catalog entry,
* mark connections depending on that entry as needing to be remade.
* We can't immediately destroy them, since they might be in the midst of
* a transaction, but we'll remake them at the next opportunity.
*
* Although most cache invalidation callbacks blow away all the related stuff
* regardless of the given hashvalue, connections are expensive enough that
* it's worth trying to avoid that.
*
* NB: We could avoid unnecessary disconnection more strictly by examining
* individual option values, but it seems too much effort for the gain.
*/
static void
pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue)
{
HASH_SEQ_STATUS scan;
ConnCacheEntry *entry;
Assert(cacheid == FOREIGNSERVEROID || cacheid == USERMAPPINGOID);
/* ConnectionHash must exist already, if we're registered */
hash_seq_init(&scan, ConnectionHash);
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
{
/* Ignore invalid entries */
if (entry->conn == NULL)
continue;
/* hashvalue == 0 means a cache reset, must clear all state */
if (hashvalue == 0 ||
(cacheid == FOREIGNSERVEROID &&
entry->server_hashvalue == hashvalue) ||
(cacheid == USERMAPPINGOID &&
entry->mapping_hashvalue == hashvalue))
entry->invalidated = true;
}
}
/*
* Raise an error if the given connection cache entry is marked as being
* in the middle of an xact state change. This should be called at which no
* such change is expected to be in progress; if one is found to be in
* progress, it means that we aborted in the middle of a previous state change
* and now don't know what the remote transaction state actually is.
* Such connections can't safely be further used. Re-establishing the
* connection would change the snapshot and roll back any writes already
* performed, so that's not an option, either. Thus, we must abort.
*/
static void
pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry)
{
HeapTuple tup;
Form_pg_user_mapping umform;
ForeignServer *server;
/* nothing to do for inactive entries and entries of sane state */
if (entry->conn == NULL || !entry->changing_xact_state)
return;
/* make sure this entry is inactive */
disconnect_pg_server(entry);
/* find server name to be shown in the message below */
tup = SearchSysCache1(USERMAPPINGOID,
ObjectIdGetDatum(entry->key));
if (!HeapTupleIsValid(tup))
elog(ERROR, "cache lookup failed for user mapping %u", entry->key);
umform = (Form_pg_user_mapping) GETSTRUCT(tup);
server = GetForeignServer(umform->umserver);
ReleaseSysCache(tup);
ereport(ERROR,
(errcode(ERRCODE_CONNECTION_EXCEPTION),
errmsg("connection to server \"%s\" was lost",
server->servername)));
}
/*
* Cancel the currently-in-progress query (whose query text we do not have)
* and ignore the result. Returns true if we successfully cancel the query
* and discard any pending result, and false if not.
*/
static bool
pgfdw_cancel_query(PGconn *conn)
{
PGcancel *cancel;
char errbuf[256];
PGresult *result = NULL;
TimestampTz endtime;
/*
* If it takes too long to cancel the query and discard the result, assume
* the connection is dead.
*/
endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000);
/*
* Issue cancel request. Unfortunately, there's no good way to limit the
* amount of time that we might block inside PQgetCancel().
*/
if ((cancel = PQgetCancel(conn)))
{
if (!PQcancel(cancel, errbuf, sizeof(errbuf)))
{
ereport(WARNING,
(errcode(ERRCODE_CONNECTION_FAILURE),
errmsg("could not send cancel request: %s",
errbuf)));
PQfreeCancel(cancel);
return false;
}
PQfreeCancel(cancel);
}
/* Get and discard the result of the query. */
if (pgfdw_get_cleanup_result(conn, endtime, &result))
return false;
PQclear(result);
return true;
}
/*
* Submit a query during (sub)abort cleanup and wait up to 30 seconds for the
* result. If the query is executed without error, the return value is true.
* If the query is executed successfully but returns an error, the return
* value is true if and only if ignore_errors is set. If the query can't be
* sent or times out, the return value is false.
*/
static bool
pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors)
{
PGresult *result = NULL;
TimestampTz endtime;
/*
* If it takes too long to execute a cleanup query, assume the connection
* is dead. It's fairly likely that this is why we aborted in the first
* place (e.g. statement timeout, user cancel), so the timeout shouldn't
* be too long.
*/
endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000);
/*
* Submit a query. Since we don't use non-blocking mode, this also can
* block. But its risk is relatively small, so we ignore that for now.
*/
if (!PQsendQuery(conn, query))
{
pgfdw_report_error(WARNING, NULL, conn, false, query);
return false;
}
/* Get the result of the query. */
if (pgfdw_get_cleanup_result(conn, endtime, &result))
return false;
/* Issue a warning if not successful. */
if (PQresultStatus(result) != PGRES_COMMAND_OK)
{
pgfdw_report_error(WARNING, result, conn, true, query);
return ignore_errors;
}
PQclear(result);
return true;
}
/*
* Get, during abort cleanup, the result of a query that is in progress. This
* might be a query that is being interrupted by transaction abort, or it might
* be a query that was initiated as part of transaction abort to get the remote
* side back to the appropriate state.
*
* It's not a huge problem if we throw an ERROR here, but if we get into error
* recursion trouble, we'll end up slamming the connection shut, which will
* necessitate failing the entire toplevel transaction even if subtransactions
* were used. Try to use WARNING where we can.
*
* endtime is the time at which we should give up and assume the remote
* side is dead. Returns true if the timeout expired, otherwise false.
* Sets *result except in case of a timeout.
*/
static bool
pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result)
{
volatile bool timed_out = false;
PGresult *volatile last_res = NULL;
/* In what follows, do not leak any PGresults on an error. */
PG_TRY();
{
for (;;)
{
PGresult *res;
while (PQisBusy(conn))
{
int wc;
TimestampTz now = GetCurrentTimestamp();
long secs;
int microsecs;
long cur_timeout;
/* If timeout has expired, give up, else get sleep time. */
if (now >= endtime)
{
timed_out = true;
goto exit;
}
TimestampDifference(now, endtime, &secs, &microsecs);
/* To protect against clock skew, limit sleep to one minute. */
cur_timeout = Min(60000, secs * USECS_PER_SEC + microsecs);
/* Sleep until there's something to do */
wc = WaitLatchOrSocket(MyLatch,
WL_LATCH_SET | WL_SOCKET_READABLE |
WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
PQsocket(conn),
cur_timeout, PG_WAIT_EXTENSION);
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
/* Data available in socket? */
if (wc & WL_SOCKET_READABLE)
{
if (!PQconsumeInput(conn))
{
/* connection trouble; treat the same as a timeout */
timed_out = true;
goto exit;
}
}
}
res = PQgetResult(conn);
if (res == NULL)
break; /* query is complete */
PQclear(last_res);
last_res = res;
}
exit: ;
}
PG_CATCH();
{
PQclear(last_res);
PG_RE_THROW();
}
PG_END_TRY();
if (timed_out)
PQclear(last_res);
else
*result = last_res;
return timed_out;
}
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