/*-------------------------------------------------------------------------
*
* connection.c
* Connection management functions for postgres_fdw
*
* Portions Copyright (c) 2012-2016, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/postgres_fdw/connection.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "postgres_fdw.h"
#include "access/xact.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "utils/hsearch.h"
#include "utils/memutils.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 */
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? */
} 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 check_conn_params(const char **keywords, const char **values);
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);
/*
* 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.
*
* XXX Note that caching connections theoretically requires a mechanism to
* detect change of FDW objects to invalidate already established connections.
* We could manage that by watching for invalidation events on the relevant
* syscaches. For the moment, though, it's not clear that this would really
* be useful and not mere pedantry. We could not flush any active connections
* mid-transaction anyway.
*/
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);
}
/* 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)
{
/* initialize new hashtable entry (key is already filled in) */
entry->conn = NULL;
entry->xact_depth = 0;
entry->have_prep_stmt = false;
entry->have_error = false;
}
/*
* 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 be left in a valid empty state.)
*/
if (entry->conn == NULL)
{
ForeignServer *server = GetForeignServer(user->serverid);
entry->xact_depth = 0; /* just to be sure */
entry->have_prep_stmt = false;
entry->have_error = false;
entry->conn = connect_pg_server(server, user);
elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\" (user mapping oid %d, userid %d)",
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);
conn = PQconnectdbParams(keywords, values, false);
if (!conn || PQstatus(conn) != CONNECTION_OK)
{
char *connmessage;
int msglen;
/* libpq typically appends a newline, strip that */
connmessage = pstrdup(PQerrorMessage(conn));
msglen = strlen(connmessage);
if (msglen > 0 && connmessage[msglen - 1] == '\n')
connmessage[msglen - 1] = '\0';
ereport(ERROR,
(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
errmsg("could not connect to server \"%s\"",
server->servername),
errdetail_internal("%s", connmessage)));
}
/*
* 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() && !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;
}
/*
* 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)
{
int i;
/* no check required if superuser */
if (superuser())
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;
res = PQexec(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";
do_sql_command(entry->conn, sql);
entry->xact_depth = 1;
}
/*
* 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);
do_sql_command(entry->conn, sql);
entry->xact_depth++;
}
}
/*
* 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;
}
/*
* 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 = PQerrorMessage(conn);
ereport(elevel,
(errcode(sqlstate),
message_primary ? errmsg_internal("%s", message_primary) :
errmsg("unknown 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)
{
elog(DEBUG3, "closing remote transaction on connection %p",
entry->conn);
switch (event)
{
case XACT_EVENT_PARALLEL_PRE_COMMIT:
case XACT_EVENT_PRE_COMMIT:
/* Commit all remote transactions during pre-commit */
do_sql_command(entry->conn, "COMMIT TRANSACTION");
/*
* 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:
/* Assume we might have lost track of prepared statements */
entry->have_error = true;
/* If we're aborting, abort all remote transactions too */
res = PQexec(entry->conn, "ABORT TRANSACTION");
/* Note: can't throw ERROR, it would be infinite loop */
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(WARNING, res, entry->conn, true,
"ABORT TRANSACTION");
else
{
PQclear(res);
/* As above, make sure to clear any prepared stmts */
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;
}
}
/* 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)
{
elog(DEBUG3, "discarding connection %p", entry->conn);
PQfinish(entry->conn);
entry->conn = NULL;
}
}
/*
* 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)))
{
PGresult *res;
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)
{
/* Commit all remote subtransactions during pre-commit */
snprintf(sql, sizeof(sql), "RELEASE SAVEPOINT s%d", curlevel);
do_sql_command(entry->conn, sql);
}
else
{
/* Assume we might have lost track of prepared statements */
entry->have_error = true;
/* Rollback all remote subtransactions during abort */
snprintf(sql, sizeof(sql),
"ROLLBACK TO SAVEPOINT s%d; RELEASE SAVEPOINT s%d",
curlevel, curlevel);
res = PQexec(entry->conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(WARNING, res, entry->conn, true, sql);
else
PQclear(res);
}
/* OK, we're outta that level of subtransaction */
entry->xact_depth--;
}
}