in_tail: Use temp table on overflowing the limit of SQL statement

Signed-off-by: Hiroshi Hatake <hiroshi@chronosphere.io>

Author: cosmo0920

plugins/in_tail/tail_db.c

@@ -25,6 +25,8 @@
 #include "tail_sql.h"
 #include "tail_file.h"
 
+#include <inttypes.h>
+
 struct query_status {
     int id;
     int rows;
@@ -271,6 +273,132 @@ static int stmt_add_param_concat(struct flb_tail_config *ctx,
     return 0;
 }
 
+/*
+ * Scalable stale inode cleanup: use a temp table to avoid SQLite variable limits.
+ *
+ * The legacy implementation builds:
+ *   DELETE ... WHERE inode NOT IN (?,?,?,...);
+ * which requires one bound parameter per inode and fails when the number of
+ * monitored files exceeds SQLITE_LIMIT_VARIABLE_NUMBER (commonly 32766 in our
+ * bundled SQLite, but can vary).
+ */
+static int flb_tail_db_stale_file_delete_temp_table(struct flb_tail_config *ctx,
+                                                    uint64_t file_count)
+{
+    int ret;
+    int changes;
+    int txn_started = FLB_FALSE;
+    sqlite3_stmt *stmt_insert_inode = NULL;
+    struct mk_list *head;
+    struct mk_list *tmp;
+    struct flb_tail_file *file;
+
+    /* If there are no monitored files, delete everything from the DB table. */
+    if (file_count == 0) {
+        ret = flb_sqldb_query(ctx->db, "DELETE FROM in_tail_files;", NULL, NULL);
+        if (ret != FLB_OK) {
+            flb_plg_error(ctx->ins, "db: cannot delete all stale inodes (no monitored files)");
+            return -1;
+        }
+
+        changes = sqlite3_changes(ctx->db->handler);
+        flb_plg_info(ctx->ins, "db: delete unmonitored stale inodes from the database: count=%d",
+                     changes);
+        return 0;
+    }
+
+    /* Create/clear temp table holding current monitored inodes. */
+    ret = flb_sqldb_query(ctx->db,
+                          "CREATE TEMP TABLE IF NOT EXISTS in_tail_current_inodes ("
+                          "  inode INTEGER PRIMARY KEY"
+                          ");",
+                          NULL, NULL);
+    if (ret != FLB_OK) {
+        flb_plg_error(ctx->ins, "db: cannot create temp table for inode cleanup");
+        return -1;
+    }
+
+    ret = flb_sqldb_query(ctx->db, "DELETE FROM in_tail_current_inodes;", NULL, NULL);
+    if (ret != FLB_OK) {
+        flb_plg_error(ctx->ins, "db: cannot clear temp inode table");
+        return -1;
+    }
+
+    /* Use a transaction for faster bulk inserts. */
+    ret = flb_sqldb_query(ctx->db, "BEGIN;", NULL, NULL);
+    if (ret != FLB_OK) {
+        flb_plg_error(ctx->ins, "db: cannot begin transaction for temp inode inserts");
+        return -1;
+    }
+    txn_started = FLB_TRUE;
+
+    ret = sqlite3_prepare_v2(ctx->db->handler,
+                             "INSERT OR IGNORE INTO in_tail_current_inodes(inode) VALUES (?);",
+                             -1, &stmt_insert_inode, 0);
+    if (ret != SQLITE_OK) {
+        flb_plg_error(ctx->ins, "db: cannot prepare temp inode insert statement, ret=%d", ret);
+        goto error;
+    }
+
+    mk_list_foreach_safe(head, tmp, &ctx->files_static) {
+        file = mk_list_entry(head, struct flb_tail_file, _head);
+
+        ret = sqlite3_bind_int64(stmt_insert_inode, 1, (sqlite3_int64) file->inode);
+        if (ret != SQLITE_OK) {
+            flb_plg_error(ctx->ins, "db: error binding temp inode insert: inode=%" PRIu64 ", ret=%d",
+                          file->inode, ret);
+            goto error;
+        }
+
+        ret = sqlite3_step(stmt_insert_inode);
+        if (ret != SQLITE_DONE) {
+            flb_plg_error(ctx->ins, "db: error inserting inode into temp table: inode=%" PRIu64 ", ret=%d",
+                          file->inode, ret);
+            goto error;
+        }
+
+        sqlite3_clear_bindings(stmt_insert_inode);
+        sqlite3_reset(stmt_insert_inode);
+    }
+
+    sqlite3_finalize(stmt_insert_inode);
+    stmt_insert_inode = NULL;
+
+    /* Delete any inode that is not in the current monitored set. */
+    ret = flb_sqldb_query(ctx->db,
+                          "DELETE FROM in_tail_files "
+                          "WHERE inode NOT IN (SELECT inode FROM in_tail_current_inodes);",
+                          NULL, NULL);
+    if (ret != FLB_OK) {
+        flb_plg_error(ctx->ins, "db: cannot delete stale inodes using temp table");
+        goto error;
+    }
+
+    ret = flb_sqldb_query(ctx->db, "COMMIT;", NULL, NULL);
+    if (ret != FLB_OK) {
+        flb_plg_error(ctx->ins, "db: cannot commit transaction for temp inode inserts");
+        goto error;
+    }
+    txn_started = FLB_FALSE;
+
+    changes = sqlite3_changes(ctx->db->handler);
+    flb_plg_info(ctx->ins, "db: delete unmonitored stale inodes from the database: count=%d",
+                 changes);
+    return 0;
+
+error:
+    if (stmt_insert_inode) {
+        sqlite3_finalize(stmt_insert_inode);
+    }
+
+    if (txn_started == FLB_TRUE) {
+        /* Best-effort rollback */
+        flb_sqldb_query(ctx->db, "ROLLBACK;", NULL, NULL);
+    }
+
+    return -1;
+}
+
 int flb_tail_db_file_set(struct flb_tail_file *file,
                          struct flb_tail_config *ctx)
 {
@@ -430,6 +558,7 @@ int flb_tail_db_stale_file_delete(struct flb_input_instance *ins,
     size_t sql_size;
     uint64_t idx;
     uint64_t file_count = ctx->files_static_count;
+    int max_vars = -1;
     flb_sds_t stale_delete_sql;
     flb_sds_t sds_tmp;
     sqlite3_stmt *stmt_delete_inodes = NULL;
@@ -441,6 +570,23 @@ int flb_tail_db_stale_file_delete(struct flb_input_instance *ins,
         return 0;
     }
 
+    /*
+     * Avoid SQLite variable limits for large monitored file sets.
+     *
+     * sqlite3_limit(..., SQLITE_LIMIT_VARIABLE_NUMBER, -1) returns the current
+     * runtime limit (compile-time hard limit may be higher). If our monitored
+     * file count exceeds this, the legacy NOT IN (?,?,...) statement will fail
+     * at prepare-time.
+     */
+    max_vars = sqlite3_limit(ctx->db->handler, SQLITE_LIMIT_VARIABLE_NUMBER, -1);
+    if (max_vars > 0 && file_count > (uint64_t) max_vars) {
+        flb_plg_warn(ctx->ins,
+                     "db: large file set detected (%" PRIu64 " files) exceeds SQLite variable limit (%d); "
+                     "using temp-table cleanup for stale inode deletion",
+                     file_count, max_vars);
+        return flb_tail_db_stale_file_delete_temp_table(ctx, file_count);
+    }
+
     ret = tail_db_lock(ctx);
     if (ret != 0) {
         flb_plg_error(ctx->ins, "db: could not acquire lock");
@@ -454,7 +600,13 @@ int flb_tail_db_stale_file_delete(struct flb_input_instance *ins,
     sql_size += SQL_STMT_PARAM_END_LEN;
     sql_size += SQL_STMT_END_LEN;
     if (file_count > 0) {
-        sql_size += (SQL_STMT_ADD_PARAM_LEN * file_count);
+        /*
+         * We already account for the first '?' via SQL_STMT_START_PARAM_LEN.
+         * Additional parameters are count-1 occurrences of ",?".
+         */
+        if (file_count > 1) {
+            sql_size += (SQL_STMT_ADD_PARAM_LEN * (file_count - 1));
+        }
     }
 
     stale_delete_sql = flb_sds_create_size(sql_size + 1);