Improve performance of dumpSequenceData().

As one might guess, this function dumps the sequence data.  It is
called once per sequence, and each such call executes a query to
retrieve the relevant data for a single sequence.  This can cause
pg_dump to take significantly longer, especially when there are
many sequences.

This commit improves the performance of this function by gathering
all the sequence data with a single query at the beginning of
pg_dump.  This information is stored in a sorted array that
dumpSequenceData() can bsearch() for what it needs.  This follows a
similar approach as previous commits that introduced sorted arrays
for role information, pg_class information, and sequence metadata.
As with those commits, this patch will cause pg_dump to use more
memory, but that isn't expected to be too egregious.

Note that we use the brand new function pg_sequence_read_tuple() in
the query that gathers all sequence data, so we must continue to
use the preexisting query-per-sequence approach for versions older
than 18.

Reviewed-by: Euler Taveira, Michael Paquier, Tom Lane
Discussion: https://postgr.es/m/20240503025140.GA1227404%40nathanxps13

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index d4e6694cc929eb8fa7c1c63eb2f07c4788139ecc..0d0251627384ba9143b9e09735cd83850228ec49 100644 (file)
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -132,6 +132,8 @@ typedef struct
    int64       startv;         /* start value */
    int64       incby;          /* increment value */
    int64       cache;          /* cache size */
+   int64       last_value;     /* last value of sequence */
+   bool        is_called;      /* whether nextval advances before returning */
 } SequenceItem;
 
 typedef enum OidOptions
@@ -17330,16 +17332,30 @@ collectSequences(Archive *fout)
     * Before Postgres 10, sequence metadata is in the sequence itself.  With
     * some extra effort, we might be able to use the sorted table for those
     * versions, but for now it seems unlikely to be worth it.
+    *
+    * Since version 18, we can gather the sequence data in this query with
+    * pg_sequence_read_tuple(), but we only do so for non-schema-only dumps.
     */
    if (fout->remoteVersion < 100000)
        return;
-   else
+   else if (fout->remoteVersion < 180000 ||
+            (fout->dopt->schemaOnly && !fout->dopt->sequence_data))
        query = "SELECT seqrelid, format_type(seqtypid, NULL), "
            "seqstart, seqincrement, "
            "seqmax, seqmin, "
-           "seqcache, seqcycle "
+           "seqcache, seqcycle, "
+           "NULL, 'f' "
            "FROM pg_catalog.pg_sequence "
            "ORDER BY seqrelid";
+   else
+       query = "SELECT seqrelid, format_type(seqtypid, NULL), "
+           "seqstart, seqincrement, "
+           "seqmax, seqmin, "
+           "seqcache, seqcycle, "
+           "last_value, is_called "
+           "FROM pg_catalog.pg_sequence, "
+           "pg_sequence_read_tuple(seqrelid) "
+           "ORDER BY seqrelid;";
 
    res = ExecuteSqlQuery(fout, query, PGRES_TUPLES_OK);
 
@@ -17356,6 +17372,8 @@ collectSequences(Archive *fout)
        sequences[i].minv = strtoi64(PQgetvalue(res, i, 5), NULL, 10);
        sequences[i].cache = strtoi64(PQgetvalue(res, i, 6), NULL, 10);
        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);
    }
 
    PQclear(res);
@@ -17622,30 +17640,59 @@ static void
 dumpSequenceData(Archive *fout, const TableDataInfo *tdinfo)
 {
    TableInfo  *tbinfo = tdinfo->tdtable;
-   PGresult   *res;
-   char       *last;
+   int64       last;
    bool        called;
    PQExpBuffer query = createPQExpBuffer();
 
-   appendPQExpBuffer(query,
-                     "SELECT last_value, is_called FROM %s",
-                     fmtQualifiedDumpable(tbinfo));
+   /*
+    * For versions >= 18, the sequence information is gathered in the sorted
+    * array before any calls to dumpSequenceData().  See collectSequences()
+    * for more information.
+    *
+    * For older versions, we have to query the sequence relations
+    * individually.
+    */
+   if (fout->remoteVersion < 180000)
+   {
+       PGresult   *res;
 
-   res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
+       appendPQExpBuffer(query,
+                         "SELECT last_value, is_called FROM %s",
+                         fmtQualifiedDumpable(tbinfo));
 
-   if (PQntuples(res) != 1)
-       pg_fatal(ngettext("query to get data of sequence \"%s\" returned %d row (expected 1)",
-                         "query to get data of sequence \"%s\" returned %d rows (expected 1)",
-                         PQntuples(res)),
-                tbinfo->dobj.name, PQntuples(res));
+       res = ExecuteSqlQuery(fout, query->data, PGRES_TUPLES_OK);
 
-   last = PQgetvalue(res, 0, 0);
-   called = (strcmp(PQgetvalue(res, 0, 1), "t") == 0);
+       if (PQntuples(res) != 1)
+           pg_fatal(ngettext("query to get data of sequence \"%s\" returned %d row (expected 1)",
+                             "query to get data of sequence \"%s\" returned %d rows (expected 1)",
+                             PQntuples(res)),
+                    tbinfo->dobj.name, PQntuples(res));
+
+       last = strtoi64(PQgetvalue(res, 0, 0), NULL, 10);
+       called = (strcmp(PQgetvalue(res, 0, 1), "t") == 0);
+
+       PQclear(res);
+   }
+   else
+   {
+       SequenceItem key = {0};
+       SequenceItem *entry;
+
+       Assert(sequences);
+       Assert(tbinfo->dobj.catId.oid);
+
+       key.oid = tbinfo->dobj.catId.oid;
+       entry = bsearch(&key, sequences, nsequences,
+                       sizeof(SequenceItem), SequenceItemCmp);
+
+       last = entry->last_value;
+       called = entry->is_called;
+   }
 
    resetPQExpBuffer(query);
    appendPQExpBufferStr(query, "SELECT pg_catalog.setval(");
    appendStringLiteralAH(query, fmtQualifiedDumpable(tbinfo), fout);
-   appendPQExpBuffer(query, ", %s, %s);\n",
+   appendPQExpBuffer(query, ", " INT64_FORMAT ", %s);\n",
                      last, (called ? "true" : "false"));
 
    if (tdinfo->dobj.dump & DUMP_COMPONENT_DATA)
@@ -17659,8 +17706,6 @@ dumpSequenceData(Archive *fout, const TableDataInfo *tdinfo)
                                  .deps = &(tbinfo->dobj.dumpId),
                                  .nDeps = 1));
 
-   PQclear(res);
-
    destroyPQExpBuffer(query);
 }