@ -16,12 +16,14 @@
# include "access/xact.h"
# include "catalog/pg_user_mapping.h"
# include "commands/defrem.h"
# include "funcapi.h"
# include "mb/pg_wchar.h"
# include "miscadmin.h"
# include "pgstat.h"
# include "postgres_fdw.h"
# include "storage/fd.h"
# include "storage/latch.h"
# include "utils/builtins.h"
# include "utils/datetime.h"
# include "utils/hsearch.h"
# include "utils/inval.h"
@ -74,6 +76,11 @@ static unsigned int prep_stmt_number = 0;
/* tracks whether any work is needed in callback functions */
static bool xact_got_connection = false ;
/*
* SQL functions
*/
PG_FUNCTION_INFO_V1 ( postgres_fdw_get_connections ) ;
/* prototypes of private functions */
static void make_new_connection ( ConnCacheEntry * entry , UserMapping * user ) ;
static PGconn * connect_pg_server ( ForeignServer * server , UserMapping * user ) ;
@ -1335,3 +1342,131 @@ exit: ;
* result = last_res ;
return timed_out ;
}
/*
* List active foreign server connections .
*
* This function takes no input parameter and returns setof record made of
* following values :
* - server_name - server name of active connection . In case the foreign server
* is dropped but still the connection is active , then the server name will
* be NULL in output .
* - valid - true / false representing whether the connection is valid or not .
* Note that the connections can get invalidated in pgfdw_inval_callback .
*
* No records are returned when there are no cached connections at all .
*/
Datum
postgres_fdw_get_connections ( PG_FUNCTION_ARGS )
{
# define POSTGRES_FDW_GET_CONNECTIONS_COLS 2
ReturnSetInfo * rsinfo = ( ReturnSetInfo * ) fcinfo - > resultinfo ;
TupleDesc tupdesc ;
Tuplestorestate * tupstore ;
MemoryContext per_query_ctx ;
MemoryContext oldcontext ;
HASH_SEQ_STATUS scan ;
ConnCacheEntry * entry ;
/* check to see if caller supports us returning a tuplestore */
if ( rsinfo = = NULL | | ! IsA ( rsinfo , ReturnSetInfo ) )
ereport ( ERROR ,
( errcode ( ERRCODE_FEATURE_NOT_SUPPORTED ) ,
errmsg ( " set-valued function called in context that cannot accept a set " ) ) ) ;
if ( ! ( rsinfo - > allowedModes & SFRM_Materialize ) )
ereport ( ERROR ,
( errcode ( ERRCODE_FEATURE_NOT_SUPPORTED ) ,
errmsg ( " materialize mode required, but it is not allowed in this context " ) ) ) ;
/* Build a tuple descriptor for our result type */
if ( get_call_result_type ( fcinfo , NULL , & tupdesc ) ! = TYPEFUNC_COMPOSITE )
elog ( ERROR , " return type must be a row type " ) ;
/* Build tuplestore to hold the result rows */
per_query_ctx = rsinfo - > econtext - > ecxt_per_query_memory ;
oldcontext = MemoryContextSwitchTo ( per_query_ctx ) ;
tupstore = tuplestore_begin_heap ( true , false , work_mem ) ;
rsinfo - > returnMode = SFRM_Materialize ;
rsinfo - > setResult = tupstore ;
rsinfo - > setDesc = tupdesc ;
MemoryContextSwitchTo ( oldcontext ) ;
/* If cache doesn't exist, we return no records */
if ( ! ConnectionHash )
{
/* clean up and return the tuplestore */
tuplestore_donestoring ( tupstore ) ;
PG_RETURN_VOID ( ) ;
}
hash_seq_init ( & scan , ConnectionHash ) ;
while ( ( entry = ( ConnCacheEntry * ) hash_seq_search ( & scan ) ) )
{
ForeignServer * server ;
Datum values [ POSTGRES_FDW_GET_CONNECTIONS_COLS ] ;
bool nulls [ POSTGRES_FDW_GET_CONNECTIONS_COLS ] ;
/* We only look for open remote connections */
if ( ! entry - > conn )
continue ;
server = GetForeignServerExtended ( entry - > serverid , FSV_MISSING_OK ) ;
MemSet ( values , 0 , sizeof ( values ) ) ;
MemSet ( nulls , 0 , sizeof ( nulls ) ) ;
/*
* The foreign server may have been dropped in current explicit
* transaction . It is not possible to drop the server from another
* session when the connection associated with it is in use in the
* current transaction , if tried so , the drop query in another session
* blocks until the current transaction finishes .
*
* Even though the server is dropped in the current transaction , the
* cache can still have associated active connection entry , say we
* call such connections dangling . Since we can not fetch the server
* name from system catalogs for dangling connections , instead we
* show NULL value for server name in output .
*
* We could have done better by storing the server name in the cache
* entry instead of server oid so that it could be used in the output .
* But the server name in each cache entry requires 64 bytes of
* memory , which is huge , when there are many cached connections and
* the use case i . e . dropping the foreign server within the explicit
* current transaction seems rare . So , we chose to show NULL value for
* server name in output .
*
* Such dangling connections get closed either in next use or at the
* end of current explicit transaction in pgfdw_xact_callback .
*/
if ( ! server )
{
/*
* If the server has been dropped in the current explicit
* transaction , then this entry would have been invalidated in
* pgfdw_inval_callback at the end of drop sever command . Note
* that this connection would not have been closed in
* pgfdw_inval_callback because it is still being used in the
* current explicit transaction . So , assert that here .
*/
Assert ( entry - > conn & & entry - > xact_depth > 0 & & entry - > invalidated ) ;
/* Show null, if no server name was found */
nulls [ 0 ] = true ;
}
else
values [ 0 ] = CStringGetTextDatum ( server - > servername ) ;
values [ 1 ] = BoolGetDatum ( ! entry - > invalidated ) ;
tuplestore_putvalues ( tupstore , tupdesc , values , nulls ) ;
}
/* clean up and return the tuplestore */
tuplestore_donestoring ( tupstore ) ;
PG_RETURN_VOID ( ) ;
}
Fujii Masao
5 years ago