PG-286: Fix deadlock.
Can't call elog() function from inside the pgsm_log as the pgss_hash lock could be already acquired in exclusive mode, since elog() triggers the psmg_emit_log hook, when it calls pgss_store it will try to acquire the pgss_hash lock again, leading to a deadlock.pull/184/head
Diego Fronza
Hamid Akhtar
parent
82031ed52c
commit
fb4f632027
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@ -0,0 +1,223 @@
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/*-------------------------------------------------------------------------
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*
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* pgsm_errors.c
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* Track pg_stat_monitor internal error messages.
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*
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* Copyright © 2021, Percona LLC and/or its affiliates
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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*
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* Portions Copyright (c) 1994, The Regents of the University of California
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*
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* IDENTIFICATION
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* contrib/pg_stat_monitor/pgsm_errors.c
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*
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*-------------------------------------------------------------------------
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*/
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#include <stdarg.h>
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#include <stdbool.h>
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#include <string.h>
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#include <time.h>
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#include <sys/time.h>
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#include <postgres.h>
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#include <access/hash.h>
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#include <storage/shmem.h>
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#include <utils/hsearch.h>
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#include "pg_stat_monitor.h"
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#include "pgsm_errors.h"
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PG_FUNCTION_INFO_V1(pg_stat_monitor_errors);
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PG_FUNCTION_INFO_V1(pg_stat_monitor_reset_errors);
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/*
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* Maximum number of error messages tracked.
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* This should be set to a sensible value in order to track
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* the different type of errors that pg_stat_monitor may
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* report, e.g. out of memory.
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*/
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#define PSGM_ERRORS_MAX 128
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static HTAB *pgsm_errors_ht = NULL;
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void psgm_errors_init(void)
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{
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HASHCTL info;
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#if PG_VERSION_NUM >= 140000
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int flags = HASH_ELEM | HASH_STRINGS;
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#else
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int flags = HASH_ELEM | HASH_BLOBS;
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#endif
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memset(&info, 0, sizeof(info));
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info.keysize = ERROR_MSG_MAX_LEN;
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info.entrysize = sizeof(ErrorEntry);
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pgsm_errors_ht = ShmemInitHash("pg_stat_monitor: errors hashtable",
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PSGM_ERRORS_MAX, /* initial size */
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PSGM_ERRORS_MAX, /* maximum size */
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&info,
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flags);
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}
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size_t pgsm_errors_size(void)
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{
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return hash_estimate_size(PSGM_ERRORS_MAX, sizeof(ErrorEntry));
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}
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void pgsm_log(PgsmLogSeverity severity, const char *format, ...)
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{
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char key[ERROR_MSG_MAX_LEN];
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ErrorEntry *entry;
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bool found = false;
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va_list ap;
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int n;
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struct timeval tv;
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struct tm *lt;
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pgssSharedState *pgss;
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va_start(ap, format);
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n = vsnprintf(key, ERROR_MSG_MAX_LEN, format, ap);
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va_end(ap);
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if (n < 0)
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return;
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pgss = pgsm_get_ss();
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LWLockAcquire(pgss->errors_lock, LW_EXCLUSIVE);
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entry = (ErrorEntry *) hash_search(pgsm_errors_ht, key, HASH_ENTER_NULL, &found);
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if (!entry)
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{
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LWLockRelease(pgss->errors_lock);
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/*
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* We're out of memory, can't track this error message.
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*/
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return;
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}
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if (!found)
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{
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entry->severity = severity;
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entry->calls = 0;
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}
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/* Update message timestamp. */
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gettimeofday(&tv, NULL);
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lt = localtime(&tv.tv_sec);
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snprintf(entry->time, sizeof(entry->time),
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"%04d-%02d-%02d %02d:%02d:%02d",
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lt->tm_year + 1900,
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lt->tm_mon + 1,
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lt->tm_mday,
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lt->tm_hour,
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lt->tm_min,
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lt->tm_sec);
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entry->calls++;
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LWLockRelease(pgss->errors_lock);
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}
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/*
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* Clear all entries from the hash table.
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*/
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Datum
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pg_stat_monitor_reset_errors(PG_FUNCTION_ARGS)
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{
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HASH_SEQ_STATUS hash_seq;
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ErrorEntry *entry;
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pgssSharedState *pgss = pgsm_get_ss();
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/* Safety check... */
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if (!IsSystemInitialized())
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ereport(ERROR,
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(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
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errmsg("pg_stat_monitor: must be loaded via shared_preload_libraries")));
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LWLockAcquire(pgss->errors_lock, LW_EXCLUSIVE);
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hash_seq_init(&hash_seq, pgsm_errors_ht);
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while ((entry = hash_seq_search(&hash_seq)) != NULL)
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entry = hash_search(pgsm_errors_ht, &entry->message, HASH_REMOVE, NULL);
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LWLockRelease(pgss->errors_lock);
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PG_RETURN_VOID();
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}
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/*
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* Invoked when users query the view pg_stat_monitor_errors.
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* This function creates tuples with error messages from data present in
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* the hash table, then return the dataset to the caller.
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*/
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Datum
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pg_stat_monitor_errors(PG_FUNCTION_ARGS)
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{
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ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
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TupleDesc tupdesc;
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Tuplestorestate *tupstore;
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MemoryContext per_query_ctx;
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MemoryContext oldcontext;
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HASH_SEQ_STATUS hash_seq;
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ErrorEntry *error_entry;
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pgssSharedState *pgss = pgsm_get_ss();
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/* Safety check... */
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if (!IsSystemInitialized())
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ereport(ERROR,
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(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
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errmsg("pg_stat_monitor: must be loaded via shared_preload_libraries")));
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/* check to see if caller supports us returning a tuplestore */
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if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("pg_stat_monitor: set-valued function called in context that cannot accept a set")));
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/* Switch into long-lived context to construct returned data structures */
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per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
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oldcontext = MemoryContextSwitchTo(per_query_ctx);
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/* Build a tuple descriptor for our result type */
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if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
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elog(ERROR, "pg_stat_monitor: return type must be a row type");
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if (tupdesc->natts != 4)
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elog(ERROR, "pg_stat_monitor: incorrect number of output arguments, required 3, found %d", tupdesc->natts);
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tupstore = tuplestore_begin_heap(true, false, work_mem);
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rsinfo->returnMode = SFRM_Materialize;
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rsinfo->setResult = tupstore;
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rsinfo->setDesc = tupdesc;
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MemoryContextSwitchTo(oldcontext);
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LWLockAcquire(pgss->errors_lock, LW_SHARED);
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hash_seq_init(&hash_seq, pgsm_errors_ht);
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while ((error_entry = hash_seq_search(&hash_seq)) != NULL)
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{
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Datum values[4];
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bool nulls[4];
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int i = 0;
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memset(values, 0, sizeof(values));
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memset(nulls, 0, sizeof(nulls));
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values[i++] = Int64GetDatumFast(error_entry->severity);
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values[i++] = CStringGetTextDatum(error_entry->message);
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values[i++] = CStringGetTextDatum(error_entry->time);
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values[i++] = Int64GetDatumFast(error_entry->calls);
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tuplestore_putvalues(tupstore, tupdesc, values, nulls);
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}
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LWLockRelease(pgss->errors_lock);
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/* clean up and return the tuplestore */
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tuplestore_donestoring(tupstore);
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return (Datum)0;
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}
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