On Thu, Jan 26, 2017 at 6:04 PM, vinayak
<pokale_vinayak...@lab.ntt.co.jp> wrote:
> Hi Sawada-san,
>
> On 2017/01/26 16:51, Masahiko Sawada wrote:
>
> Thank you for reviewing!
>
> I think this is a bug of pg_fdw_resolver contrib module. I had
> forgotten to change the SQL executed by pg_fdw_resolver process.
> Attached latest version 002 patch.
>
> As previous version patch conflicts to current HEAD, attached updated
> version patches. Also I fixed some bugs in pg_fdw_xact_resolver and
> added some documentations.
> Please review it.
>
> Thank you updating the patches.
>
> I have applied patches on Postgres HEAD.
> I have created the postgres=fdw extension in PostgreSQL and then I got
> segmentation fault.
> Details:
> =# 2017-01-26 17:52:56.156 JST [3411] LOG: worker process: foreign
> transaction resolver launcher (PID 3418) was terminated by signal 11:
> Segmentation fault
> 2017-01-26 17:52:56.156 JST [3411] LOG: terminating any other active server
> processes
> 2017-01-26 17:52:56.156 JST [3425] WARNING: terminating connection because
> of crash of another server process
> 2017-01-26 17:52:56.156 JST [3425] DETAIL: The postmaster has commanded
> this server process to roll back the current transaction and exit, because
> another server process exited abnormally and possibly corrupted shared
> memory.
> 2017-01-26 17:52:56.156 JST [3425] HINT: In a moment you should be able to
> reconnect to the database and repeat your command.
>
> Is this a bug?
>
Thank you for testing!
Sorry, I attached wrong version patch of pg_fdw_xact_resovler. Please
use attached patch.
Regards,
--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
diff --git a/contrib/pg_fdw_xact_resolver/Makefile b/contrib/pg_fdw_xact_resolver/Makefile
new file mode 100644
index 0000000..f8924f0
--- /dev/null
+++ b/contrib/pg_fdw_xact_resolver/Makefile
@@ -0,0 +1,15 @@
+# contrib/pg_fdw_xact_resolver/Makefile
+
+MODULES = pg_fdw_xact_resolver
+PGFILEDESC = "pg_fdw_xact_resolver - foreign transaction resolver demon"
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/pg_fdw_xact_resolver
+top_builddir = ../../
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif
diff --git a/contrib/pg_fdw_xact_resolver/pg_fdw_xact_resolver.c b/contrib/pg_fdw_xact_resolver/pg_fdw_xact_resolver.c
new file mode 100644
index 0000000..c57de0a
--- /dev/null
+++ b/contrib/pg_fdw_xact_resolver/pg_fdw_xact_resolver.c
@@ -0,0 +1,453 @@
+/* -------------------------------------------------------------------------
+ *
+ * pg_fdw_xact_resolver.c
+ *
+ * Contrib module to launch foreign transaction resolver to resolve unresolved
+ * transactions prepared on foreign servers.
+ *
+ * The extension launches foreign transaction resolver launcher process as a
+ * background worker. The launcher then launches separate background worker
+ * process to resolve the foreign transaction in each database. The worker
+ * process simply connects to the database specified and calls pg_fdw_xact_resolve()
+ * function, which tries to resolve the transactions. The launcher process
+ * launches at most one worker at a time.
+ *
+ * Copyright (C) 2017, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ * contrib/pg_fdw_xact_resolver/pg_fdw_xact_resolver.c
+ *
+ * -------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+/* These are always necessary for a bgworker */
+#include "miscadmin.h"
+#include "postmaster/bgworker.h"
+#include "storage/ipc.h"
+#include "storage/latch.h"
+#include "storage/lwlock.h"
+#include "storage/proc.h"
+#include "storage/shmem.h"
+
+/* these headers are used by this particular worker's code */
+#include "access/heapam.h"
+#include "access/htup_details.h"
+#include "access/xact.h"
+#include "access/fdw_xact.h"
+#include "catalog/pg_database.h"
+#include "executor/spi.h"
+#include "fmgr.h"
+#include "lib/stringinfo.h"
+#include "pgstat.h"
+#include "utils/builtins.h"
+#include "utils/snapmgr.h"
+#include "utils/timestamp.h"
+#include "tcop/utility.h"
+
+PG_MODULE_MAGIC;
+
+void _PG_init(void);
+
+/*
+ * Flags set by interrupt handlers of foreign transaction resolver for later
+ * service in the main loop.
+ */
+static volatile sig_atomic_t got_sighup = false;
+static volatile sig_atomic_t got_sigterm = false;
+static volatile sig_atomic_t got_sigquit = false;
+static volatile sig_atomic_t got_sigusr1 = false;
+
+static void FDWXactResolver_worker_main(Datum dbid_datum);
+static void FDWXactResolverMain(Datum main_arg);
+static List *get_database_list(void);
+
+/* GUC variable */
+static int fx_resolver_naptime;
+
+/*
+ * Signal handler for SIGTERM
+ * Set a flag to let the main loop to terminate, and set our latch to wake
+ * it up.
+ */
+static void
+FDWXactResolver_SIGTERM(SIGNAL_ARGS)
+{
+ int save_errno = errno;
+
+ got_sigterm = true;
+ SetLatch(MyLatch);
+
+ errno = save_errno;
+}
+
+/*
+ * Signal handler for SIGQUIT
+ * Set a flag to let the main loop to terminate, and set our latch to wake
+ * it up.
+ */
+static void
+FDWXactResolver_SIGQUIT(SIGNAL_ARGS)
+{
+ int save_errno = errno;
+
+ got_sigquit = true;
+ SetLatch(MyLatch);
+
+ errno = save_errno;
+}
+/*
+ * Signal handler for SIGHUP
+ * Set a flag to tell the main loop to reread the config file, and set
+ * our latch to wake it up.
+ */
+static void
+FDWXactResolver_SIGHUP(SIGNAL_ARGS)
+{
+ int save_errno = errno;
+
+ got_sighup = true;
+ SetLatch(MyLatch);
+
+ errno = save_errno;
+}
+
+static void
+FDWXactResolver_SIGUSR1(SIGNAL_ARGS)
+{
+ int save_errno = errno;
+
+ got_sigusr1 = true;
+ SetLatch(MyLatch);
+
+ errno = save_errno;
+}
+
+/*
+ * Entrypoint of this module.
+ *
+ * Launches the foreign transaction resolver demon.
+ */
+void
+_PG_init(void)
+{
+ BackgroundWorker worker;
+
+ if (!process_shared_preload_libraries_in_progress)
+ return;
+
+ DefineCustomIntVariable("pg_fdw_xact_resolver.naptime",
+ "Time to sleep between pg_fdw_xact_resolver runs.",
+ NULL,
+ &fx_resolver_naptime,
+ 60,
+ 1,
+ INT_MAX,
+ PGC_SIGHUP,
+ 0,
+ NULL, NULL, NULL);
+
+ /* set up common data for all our workers */
+ /*
+ * For some reason unless background worker set
+ * BGWORKER_BACKEND_DATABASE_CONNECTION, it's not added to BackendList and
+ * hence notification to this backend is not enabled. So set that flag even
+ * if the backend itself doesn't need database connection.
+ */
+ worker.bgw_flags = BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION;
+ worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
+ worker.bgw_restart_time = 5;
+ snprintf(worker.bgw_name, BGW_MAXLEN, "foreign transaction resolver launcher");
+ worker.bgw_main = FDWXactResolverMain;
+ worker.bgw_main_arg = (Datum) 0;/* Craft some dummy arg. */
+ worker.bgw_notify_pid = 0;
+
+ RegisterBackgroundWorker(&worker);
+}
+
+void
+FDWXactResolverMain(Datum main_arg)
+{
+ /* For launching background worker */
+ BackgroundWorker worker;
+ BackgroundWorkerHandle *handle = NULL;
+ pid_t pid;
+ List *dbid_list = NIL;
+ TimestampTz launched_time = GetCurrentTimestamp();
+ TimestampTz next_launch_time = launched_time + (fx_resolver_naptime * 1000L);
+
+ ereport(LOG,
+ (errmsg("pg_fdw_xact_resolver launcher started")));
+
+ /* Properly accept or ignore signals the postmaster might send us */
+ pqsignal(SIGHUP, FDWXactResolver_SIGHUP); /* set flag to read config
+ * file */
+ pqsignal(SIGTERM, FDWXactResolver_SIGTERM); /* request shutdown */
+ pqsignal(SIGQUIT, FDWXactResolver_SIGQUIT); /* hard crash time */
+ pqsignal(SIGUSR1, FDWXactResolver_SIGUSR1);
+
+ /* Unblock signals */
+ BackgroundWorkerUnblockSignals();
+
+ /* Initialize connection */
+ BackgroundWorkerInitializeConnection(NULL, NULL);
+
+ /*
+ * Main loop: do this until the SIGTERM handler tells us to terminate
+ */
+ while (!got_sigterm)
+ {
+ int rc;
+ int naptime_msec;
+ TimestampTz current_time = GetCurrentTimestamp();
+
+ /* Determine sleep time */
+ naptime_msec = (fx_resolver_naptime * 1000L) - (current_time - launched_time);
+
+ if (naptime_msec < 0)
+ naptime_msec = 0;
+
+ /*
+ * Background workers mustn't call usleep() or any direct equivalent:
+ * instead, they may wait on their process latch, which sleeps as
+ * necessary, but is awakened if postmaster dies. That way the
+ * background process goes away immediately in an emergency.
+ */
+ rc = WaitLatch(MyLatch,
+ WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+ naptime_msec,
+ WAIT_EVENT_PG_SLEEP);
+ ResetLatch(MyLatch);
+
+ /* emergency bailout if postmaster has died */
+ if (rc & WL_POSTMASTER_DEATH)
+ proc_exit(1);
+
+ /*
+ * Postmaster wants to stop this process. Exit with non-zero code, so
+ * that the postmaster starts this process again. The worker processes
+ * will receive the signal and end themselves. This process will restart
+ * them if necessary.
+ */
+ if (got_sigquit)
+ proc_exit(2);
+
+ /* In case of a SIGHUP, just reload the configuration */
+ if (got_sighup)
+ {
+ got_sighup = false;
+ ProcessConfigFile(PGC_SIGHUP);
+ }
+
+ if (got_sigusr1)
+ {
+ got_sigusr1 = false;
+
+ /* If we had started a worker check whether it completed */
+ if (handle)
+ {
+ BgwHandleStatus status;
+
+ status = GetBackgroundWorkerPid(handle, &pid);
+ if (status == BGWH_STOPPED)
+ handle = NULL;
+ }
+ }
+
+ current_time = GetCurrentTimestamp();
+
+ /*
+ * If no background worker is running, we can start one if there are
+ * unresolved foreign transactions.
+ */
+ if (!handle &&
+ TimestampDifferenceExceeds(next_launch_time, current_time, naptime_msec))
+ {
+ Oid dbid;
+
+ /* Get the database list if empty*/
+ if (!dbid_list)
+ dbid_list = get_database_list();
+
+ /* Launch a worker if dbid_list has database */
+ if (dbid_list)
+ {
+ /* Work on the first dbid, and remove it from the list */
+ dbid = linitial_oid(dbid_list);
+ dbid_list = list_delete_oid(dbid_list, dbid);
+
+ Assert(OidIsValid(dbid));
+
+ /* Start the foreign transaction resolver */
+ worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
+ BGWORKER_BACKEND_DATABASE_CONNECTION;
+ worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
+
+ /* We will start another worker if needed */
+ worker.bgw_restart_time = BGW_NEVER_RESTART;
+ worker.bgw_main = FDWXactResolver_worker_main;
+ snprintf(worker.bgw_name, BGW_MAXLEN, "foreign transaction resolver (dbid %u)", dbid);
+ worker.bgw_main_arg = ObjectIdGetDatum(dbid);
+
+ /* set bgw_notify_pid so that we can wait for it to finish */
+ worker.bgw_notify_pid = MyProcPid;
+
+ RegisterDynamicBackgroundWorker(&worker, &handle);
+ }
+
+ /* Set next launch time */
+ launched_time = current_time;
+ next_launch_time = TimestampTzPlusMilliseconds(launched_time,
+ fx_resolver_naptime * 1000L);
+ }
+ }
+
+ /* Time to exit */
+ ereport(LOG,
+ (errmsg("foreign transaction resolver shutting down")));
+
+ proc_exit(0); /* done */
+}
+
+/* FDWXactWorker_SIGTERM
+ * Terminates the foreign transaction resolver worker process */
+static void
+FDWXactWorker_SIGTERM(SIGNAL_ARGS)
+{
+ /* Just terminate the current process */
+ proc_exit(1);
+}
+
+/* Per database foreign transaction resolver */
+static void
+FDWXactResolver_worker_main(Datum dbid_datum)
+{
+ char *command = "SELECT * FROM pg_fdw_xact_resolve() WHERE status = 'resolved'";
+ Oid dbid = DatumGetObjectId(dbid_datum);
+ int ret;
+
+ /*
+ * This background worker does not loop infinitely, so we need handler only
+ * for SIGTERM, in which case the process should just exit quickly.
+ */
+ pqsignal(SIGTERM, FDWXactWorker_SIGTERM);
+ pqsignal(SIGQUIT, FDWXactWorker_SIGTERM);
+
+ /* Unblock signals */
+ BackgroundWorkerUnblockSignals();
+
+ /*
+ * Run this background worker in superuser mode, so that all the foreign
+ * server and user information isaccessible.
+ */
+ BackgroundWorkerInitializeConnectionByOid(dbid, InvalidOid);
+
+ /*
+ * Start a transaction on which we can call resolver function.
+ * Note that each StartTransactionCommand() call should be preceded by a
+ * SetCurrentStatementStartTimestamp() call, which sets both the time
+ * for the statement we're about the run, and also the transaction
+ * start time. Also, each other query sent to SPI should probably be
+ * preceded by SetCurrentStatementStartTimestamp(), so that statement
+ * start time is always up to date.
+ *
+ * The SPI_connect() call lets us run queries through the SPI manager,
+ * and the PushActiveSnapshot() call creates an "active" snapshot
+ * which is necessary for queries to have MVCC data to work on.
+ *
+ * The pgstat_report_activity() call makes our activity visible
+ * through the pgstat views.
+ */
+ SetCurrentStatementStartTimestamp();
+ StartTransactionCommand();
+ SPI_connect();
+ PushActiveSnapshot(GetTransactionSnapshot());
+ pgstat_report_activity(STATE_RUNNING, command);
+
+ /* Run the resolver function */
+ ret = SPI_execute(command, false, 0);
+
+ if (ret < 0)
+ elog(LOG, "error running pg_fdw_xact_resolve() within database %d",
+ dbid);
+
+ if (SPI_processed > 0)
+ ereport(LOG,
+ (errmsg("resolved %lu foreign transactions", SPI_processed)));
+
+ /*
+ * And finish our transaction.
+ */
+ SPI_finish();
+ PopActiveSnapshot();
+ CommitTransactionCommand();
+ pgstat_report_activity(STATE_IDLE, NULL);
+
+ /* Done exit now */
+ proc_exit(0);
+}
+
+/* Get database list */
+static List *
+get_database_list(void)
+{
+ List *dblist = NIL;
+ ListCell *cell;
+ ListCell *next;
+ ListCell *prev = NULL;
+ HeapScanDesc scan;
+ HeapTuple tup;
+ Relation rel;
+ MemoryContext resultcxt;
+
+ /* This is the context that we will allocate our output data in */
+ resultcxt = CurrentMemoryContext;
+
+ SetCurrentStatementStartTimestamp();
+ StartTransactionCommand();
+ (void) GetTransactionSnapshot();
+
+ rel = heap_open(DatabaseRelationId, AccessShareLock);
+ scan = heap_beginscan_catalog(rel, 0, NULL);
+
+ while (HeapTupleIsValid(tup = heap_getnext(scan, ForwardScanDirection)))
+ {
+ MemoryContext oldcxt;
+
+ /*
+ * Allocate our results in the caller's context, not the
+ * transaction's. We do this inside the loop, and restore the original
+ * context at the end, so that leaky things like heap_getnext() are
+ * not called in a potentially long-lived context.
+ */
+ oldcxt = MemoryContextSwitchTo(resultcxt);
+ dblist = lappend_oid(dblist, HeapTupleGetOid(tup));
+ MemoryContextSwitchTo(oldcxt);
+ }
+
+ heap_endscan(scan);
+ heap_close(rel, AccessShareLock);
+
+ CommitTransactionCommand();
+
+ /*
+ * Check if database has foreign transaction entry. Delete entry
+ * from the list if the database has.
+ */
+ for (cell = list_head(dblist); cell != NULL; cell = next)
+ {
+ Oid dbid = lfirst_oid(cell);
+ bool exists;
+
+ next = lnext(cell);
+
+ exists = fdw_xact_exists(InvalidTransactionId, dbid, InvalidOid, InvalidOid);
+
+ if (!exists)
+ dblist = list_delete_cell(dblist, cell, prev);
+ else
+ prev = cell;
+ }
+
+ return dblist;
+}
diff --git a/doc/src/sgml/contrib.sgml b/doc/src/sgml/contrib.sgml
index c8708ec..e2048ee 100644
--- a/doc/src/sgml/contrib.sgml
+++ b/doc/src/sgml/contrib.sgml
@@ -127,6 +127,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
&passwordcheck;
&pgbuffercache;
&pgcrypto;
+ &pg-fdw-xact-resolver
&pgfreespacemap;
&pgprewarm;
&pgrowlocks;
diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml
index 2624c62..79d076c 100644
--- a/doc/src/sgml/filelist.sgml
+++ b/doc/src/sgml/filelist.sgml
@@ -133,6 +133,7 @@
<!ENTITY passwordcheck SYSTEM "passwordcheck.sgml">
<!ENTITY pgbuffercache SYSTEM "pgbuffercache.sgml">
<!ENTITY pgcrypto SYSTEM "pgcrypto.sgml">
+<!ENTITY pg-fdw-xact-resolver SYSTEM "pg-fdw-xact-resolver.sgml">
<!ENTITY pgfreespacemap SYSTEM "pgfreespacemap.sgml">
<!ENTITY pgprewarm SYSTEM "pgprewarm.sgml">
<!ENTITY pgrowlocks SYSTEM "pgrowlocks.sgml">
diff --git a/doc/src/sgml/pg-fdw-xact-resolver.sgml b/doc/src/sgml/pg-fdw-xact-resolver.sgml
new file mode 100644
index 0000000..b47073c
--- /dev/null
+++ b/doc/src/sgml/pg-fdw-xact-resolver.sgml
@@ -0,0 +1,60 @@
+<!-- doc/src/sgml/pg-fdw-xact-resolver.sgml -->
+
+<sect1 id="pg-fdw-xact-resolver" xreflabel="pg_fdw_xact_resolver">
+ <title>pg_fdw_xact_resolver</title>
+
+ <indexterm zone="pg-fdw-xact-resolver">
+ <primary>pg_fdw_xact_resolver</primary>
+ </indexterm>
+
+ <para>
+ The <filename>pg_fdw_xact_resolver</> module launches foreign transaction
+ resolver process to resolve unresolved transactions prepared on foreign
+ servers.
+ </para>
+
+ <para>
+ The transaction involving multiple foreign servers uses two-phase-commit
+ protocol when transaction commits. Any crash or connection failure
+ after transaction prepared but before commit leaves the preapred transaction
+ in unresolved state. To resolve such a dandling transaction, we need to
+ call <function>pg_fdw_xact_resolve</function>.
+ </para>
+
+ <para>
+ The foreign transaction resolver process launches separate bacground
+ worker process to resolve the dangling forign transaction in each
+ database. The process simply connects to the database as needed and
+ callls <function>pg_fdw_xact_resolve</function>. The launcher process
+ launches at most one worker at a time.
+ </para>
+
+ <sect2>
+ <title>Configuration Parameters</title>
+
+ <variablelist>
+ <varlistentry>
+ <term>
+ <varname>pg_fdw_xact_resovler.naptime</varname> (<type>integer</type>)
+ </term>
+
+ <listitem>
+ <para>
+ Specifies the minimum delay between foreign transaction resolver runs
+ on any given database. The dealy is measured in seconds, and the
+ default is one minute (1min). This parameter can only be set in
+ the <filename>postgresql.conf</filename> file of on the server
+ command line.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </sect2>
+
+ <sect2>
+ <title>Author</title>
+ <para>
+ Ahutosh Bapat <email>ashutosh.ba...@enterprisedb.com</email>, Masahiko Sawada
+ <email>sawada.m...@gmail.com</email>
+ </para>
+ </sect2>
--
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