pg_dump: Fix gathering of sequence information.

Since commit bd15b7db48, pg_dump uses pg_get_sequence_data() (née
pg_sequence_read_tuple()) to gather all sequence data in a single
query as opposed to a query per sequence.  Two related bugs have
been identified:

* If the user lacks appropriate privileges on the sequence, pg_dump
generates a setval() command with garbage values instead of
failing as expected.

* pg_dump can fail due to a concurrently dropped sequence, even if
the dropped sequence's data isn't part of the dump.

This commit fixes the above issues by 1) teaching
pg_get_sequence_data() to return nulls instead of erroring for a
missing sequence and 2) teaching pg_dump to fail if it tries to
dump the data of a sequence for which pg_get_sequence_data()
returned nulls.  Note that pg_dump may still fail due to a
concurrently dropped sequence, but it should now only do so when
the sequence data is part of the dump.  This matches the behavior
before commit bd15b7db48.

Bug: #19365
Reported-by: Paveł Tyślacki <pavel.tyslacki@gmail.com>
Suggested-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/19365-6245240d8b926327%40postgresql.org
Discussion: https://postgr.es/m/2885944.1767029161%40sss.pgh.pa.us
Backpatch-through: 18

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 904eeada5ab5dec1da25029cf7daf016103f986b..e1b808bbb6050fead372c5596fa277d3b0995c2b 100644 (file)
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -1794,7 +1794,6 @@ pg_get_sequence_data(PG_FUNCTION_ARGS)
 {
 #define PG_GET_SEQUENCE_DATA_COLS  3
    Oid         relid = PG_GETARG_OID(0);
-   SeqTable    elm;
    Relation    seqrel;
    Datum       values[PG_GET_SEQUENCE_DATA_COLS] = {0};
    bool        isnull[PG_GET_SEQUENCE_DATA_COLS] = {0};
@@ -1811,13 +1810,15 @@ pg_get_sequence_data(PG_FUNCTION_ARGS)
                       LSNOID, -1, 0);
    resultTupleDesc = BlessTupleDesc(resultTupleDesc);
 
-   init_sequence(relid, &elm, &seqrel);
+   seqrel = try_relation_open(relid, AccessShareLock);
 
    /*
-    * Return all NULLs for sequences for which we lack privileges, other
-    * sessions' temporary sequences, and unlogged sequences on standbys.
+    * Return all NULLs for missing sequences, sequences for which we lack
+    * privileges, other sessions' temporary sequences, and unlogged sequences
+    * on standbys.
     */
-   if (pg_class_aclcheck(relid, GetUserId(), ACL_SELECT) == ACLCHECK_OK &&
+   if (seqrel && seqrel->rd_rel->relkind == RELKIND_SEQUENCE &&
+       pg_class_aclcheck(relid, GetUserId(), ACL_SELECT) == ACLCHECK_OK &&
        !RELATION_IS_OTHER_TEMP(seqrel) &&
        (RelationIsPermanent(seqrel) || !RecoveryInProgress()))
    {
@@ -1838,7 +1839,8 @@ pg_get_sequence_data(PG_FUNCTION_ARGS)
    else
        memset(isnull, true, sizeof(isnull));
 
-   sequence_close(seqrel, NoLock);
+   if (seqrel)
+       relation_close(seqrel, AccessShareLock);
 
    resultHeapTuple = heap_form_tuple(resultTupleDesc, values, isnull);
    result = HeapTupleGetDatum(resultHeapTuple);

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 7df56d8b1b0fb89197fb685128aea897ab05d9d2..b9e0edf8755122485a3937ef67d4a8a681cfbcd8 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -137,6 +137,7 @@ typedef struct
    int64       cache;          /* cache size */
    int64       last_value;     /* last value of sequence */
    bool        is_called;      /* whether nextval advances before returning */
+   bool        null_seqtuple;  /* did pg_get_sequence_data return nulls? */
 } SequenceItem;
 
 typedef enum OidOptions
@@ -18959,6 +18960,7 @@ collectSequences(Archive *fout)
        sequences[i].cycled = (strcmp(PQgetvalue(res, i, 7), "t") == 0);
        sequences[i].last_value = strtoi64(PQgetvalue(res, i, 8), NULL, 10);
        sequences[i].is_called = (strcmp(PQgetvalue(res, i, 9), "t") == 0);
+       sequences[i].null_seqtuple = (PQgetisnull(res, i, 8) || PQgetisnull(res, i, 9));
    }
 
    PQclear(res);
@@ -19230,6 +19232,10 @@ dumpSequenceData(Archive *fout, const TableDataInfo *tdinfo)
    bool        called;
    PQExpBuffer query = createPQExpBuffer();
 
+   /* needn't bother if not dumping sequence data */
+   if (!fout->dopt->dumpData && !fout->dopt->sequence_data)
+       return;
+
    /*
     * For versions >= 18, the sequence information is gathered in the sorted
     * array before any calls to dumpSequenceData().  See collectSequences()
@@ -19271,6 +19277,12 @@ dumpSequenceData(Archive *fout, const TableDataInfo *tdinfo)
        entry = bsearch(&key, sequences, nsequences,
                        sizeof(SequenceItem), SequenceItemCmp);
 
+       if (entry->null_seqtuple)
+           pg_fatal("failed to get data for sequence \"%s\"; user may lack "
+                    "SELECT privilege on the sequence or the sequence may "
+                    "have been concurrently dropped",
+                    tbinfo->dobj.name);
+
        last = entry->last_value;
        called = entry->is_called;
    }