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refactor(tern): read table catalog and size estimates in one scan #1251

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Merged
aparajon merged 2 commits into from
Sep 2, 2026
Merged

refactor(tern): read table catalog and size estimates in one scan #1251

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3f7791d
refactor(tern): read table catalog and size estimates in one scan
aparajon Sep 2, 2026
011021a
docs(tern): name the variable that governs table-estimate cost
aparajon Sep 2, 2026
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61 changes: 20 additions & 41 deletions pkg/tern/local_client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1071,15 +1071,24 @@ func (c *LocalClient) pullNamespaceCatalog(ctx context.Context, db *sql.DB, name
if err := c.loadForeignKeyCatalog(ctx, db, physical, pulledTables, catalog.tables); err != nil {
return nil, err
}
if err := c.loadTableEstimates(ctx, db, physical, pulledTables, catalog.tables); err != nil {
return nil, err
}
return catalog, nil
}

// loadTableCatalog reads each pulled table's kind and comment together with its
// engine-maintained row-count and on-disk-size estimates. The estimates are
// approximations: NULL for views, and served from the data dictionary's cached
// table statistics, so they lag the live table until those statistics are
// refreshed.
//
// The estimate columns are what make this read more than the kind and comment
// alone would. information_schema_stats_expiry governs how long the cached
// statistics are reused; the first read after they expire makes the server
// refresh them per table. Kind and comment come from the data dictionary and
// are cheap either way, so they ride along on this query rather than paying for
// a second traversal of the view.
func (c *LocalClient) loadTableCatalog(ctx context.Context, db *sql.DB, physicalSchema string, pulledTables map[string]string, catalog map[string]*ternv1.TableCatalog) error {
rows, err := db.QueryContext(ctx, `
SELECT table_name, table_type, table_comment
SELECT table_name, table_type, table_comment, table_rows, data_length, index_length
FROM information_schema.tables
WHERE table_schema = ?
ORDER BY table_name`, physicalSchema)
Expand All @@ -1090,14 +1099,17 @@ func (c *LocalClient) loadTableCatalog(ctx context.Context, db *sql.DB, physical

for rows.Next() {
var tableName, tableType, tableComment string
if err := rows.Scan(&tableName, &tableType, &tableComment); err != nil {
var tableRows, dataLength, indexLength sql.NullInt64
if err := rows.Scan(&tableName, &tableType, &tableComment, &tableRows, &dataLength, &indexLength); err != nil {
return fmt.Errorf("scan table catalog for database %s physical schema %s: %w", c.config.Database, physicalSchema, err)
}
if _, ok := pulledTables[tableName]; ok {
catalog[tableName] = &ternv1.TableCatalog{
Name: tableName,
Kind: normalizedTableKind(tableType),
Comment: tableComment,
Name: tableName,
Kind: normalizedTableKind(tableType),
Comment: tableComment,
EstimatedRowCount: tableRows.Int64,
DataSizeBytes: dataLength.Int64 + indexLength.Int64,
}
}
}
Expand All @@ -1107,39 +1119,6 @@ func (c *LocalClient) loadTableCatalog(ctx context.Context, db *sql.DB, physical
return nil
}

// loadTableEstimates populates engine-maintained row-count and on-disk-size
// estimates from information_schema.tables. These are approximations (NULL for
// views, stale until statistics are refreshed) and are only loaded at DETAILED
// catalog detail.
func (c *LocalClient) loadTableEstimates(ctx context.Context, db *sql.DB, physicalSchema string, pulledTables map[string]string, catalog map[string]*ternv1.TableCatalog) error {
rows, err := db.QueryContext(ctx, `
SELECT table_name, table_rows, data_length, index_length
FROM information_schema.tables
WHERE table_schema = ?
ORDER BY table_name`, physicalSchema)
if err != nil {
return fmt.Errorf("load table estimates for database %s physical schema %s: %w", c.config.Database, physicalSchema, err)
}
defer utils.CloseAndLog(rows)

for rows.Next() {
var tableName string
var tableRows, dataLength, indexLength sql.NullInt64
if err := rows.Scan(&tableName, &tableRows, &dataLength, &indexLength); err != nil {
return fmt.Errorf("scan table estimates for database %s physical schema %s: %w", c.config.Database, physicalSchema, err)
}
if _, ok := pulledTables[tableName]; ok {
tableCatalog := ensurePulledTableCatalog(catalog, tableName)
tableCatalog.EstimatedRowCount = tableRows.Int64
tableCatalog.DataSizeBytes = dataLength.Int64 + indexLength.Int64
}
}
if err := rows.Err(); err != nil {
return fmt.Errorf("iterate table estimates for database %s physical schema %s: %w", c.config.Database, physicalSchema, err)
}
return nil
}

func (c *LocalClient) loadColumnCatalog(ctx context.Context, db *sql.DB, physicalSchema string, pulledTables map[string]string, catalog map[string]*ternv1.TableCatalog) error {
rows, err := db.QueryContext(ctx, `
SELECT table_name, column_name, column_type, is_nullable, column_default, column_comment, extra
Expand Down
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