索引 ONLINE 参数

1. 目的

IvorySQL 数据库支持在创建索引时使用 ONLINE 参数，用于在线创建索引，同时不阻塞DML操作。

2. 实现说明

2.1. 数据结构扩展

IndexStmt 新增 online_keyword 字段。

bool    transformed;        /* true when transformIndexStmt is finished */
bool    concurrent;         /* should this be a concurrent index build? */
bool    online_keyword;     /* was ONLINE keyword used (as opposed to CONCURRENTLY)? */

2.2. 语法与解析

2.2.1. 语法规则扩展

在 ora_gram.y 文件中引入一个弹性选项列表 create_index_opt_list / create_index_opt，类似现有的 rebuild_index_opt_list：

create_index_opt_list:
    create_index_opt_list create_index_opt  { $$ = lappend($1, $2); }
  | /* EMPTY */                             { $$ = NIL; }
;

create_index_opt:
    ONLINE
        { $$ = makeDefElem("online", (Node *) makeBoolean(true), @1); }
  | TABLESPACE name
        { $$ = makeDefElem("tablespace", (Node *) makeString($2), @1); }
;

修改 IndexStmt 的两个产生式，将 OptTableSpace 替换为 create_index_opt_list，并在 action 中从选项列表中提取 online 和 tablespace。

IndexStmt: CREATE opt_unique INDEX opt_concurrently opt_single_name
           ON relation_expr access_method_clause '(' index_params ')'
           opt_include opt_unique_null_treatment opt_reloptions
           create_index_opt_list where_clause
    {
        IndexStmt *n = makeNode(IndexStmt);
        bool        online = false;
        bool        online_seen = false;
        char       *tablespace = NULL;
        ListCell   *lc;

        /* 解析 create_index_opt_list，提取 online 和 tablespace */
        foreach(lc, $15)
        {
            DefElem *opt = (DefElem *) lfirst(lc);

            if (strcmp(opt->defname, "online") == 0)
            {
                if (online_seen)
                    ereport(ERROR,
                            (errcode(ERRCODE_SYNTAX_ERROR),
                             errmsg("ONLINE specified multiple times"),
                             parser_errposition(opt->location)));
                online = defGetBoolean(opt);
                online_seen = true;
            }
            else if (strcmp(opt->defname, "tablespace") == 0)
            {
                if (tablespace != NULL)
                    ereport(ERROR,
                            (errcode(ERRCODE_SYNTAX_ERROR),
                             errmsg("TABLESPACE specified multiple times"),
                             parser_errposition(opt->location)));
                tablespace = defGetString(opt);
            }
        }

        /* CONCURRENTLY 与 ONLINE 互斥 */
        if ($4 && online)
            ereport(ERROR,
                    (errcode(ERRCODE_SYNTAX_ERROR),
                     errmsg("cannot use both CONCURRENTLY and ONLINE"),
                     parser_errposition(@4)));

        n->unique          = $2;
        n->concurrent      = $4 || online;
        n->online_keyword  = online;
        n->idxname         = $5;
        n->relation        = $7;
        n->accessMethod    = $8;
        n->indexParams     = $10;
        n->indexIncludingParams = $12;
        n->nulls_not_distinct   = !$13;
        n->options         = $14;       /* opt_reloptions (WITH clause) */
        n->tableSpace      = tablespace;
        n->whereClause     = $16;
        n->excludeOpNames  = NIL;
        n->idxcomment      = NULL;
        n->indexOid        = InvalidOid;
        n->oldNumber       = InvalidRelFileNumber;
        n->oldCreateSubid  = InvalidSubTransactionId;
        n->oldFirstRelfilelocatorSubid = InvalidSubTransactionId;
        n->primary         = false;
        n->isconstraint    = false;
        n->deferrable      = false;
        n->initdeferred    = false;
        n->transformed     = false;
        n->if_not_exists   = false;
        n->reset_default_tblspc = false;
        $$ = (Node *) n;
    }

2.2.2. 执行层修改（indexcmds.c）

DefineIndex() 中已有临时表降级逻辑（concurrent = false when temp table），需在相同位置补充分区表的降级逻辑：

/* 已有：临时表降级 */
if (stmt->concurrent && get_rel_persistence(tableId) != RELPERSISTENCE_TEMP)
    concurrent = true;
else
    concurrent = false;

/* 新增：分区表降级
 * Oracle 对分区表 CREATE INDEX ONLINE 返回成功（全局非分区索引）。
 * PostgreSQL 的 concurrent + partitioned 路径会报错，因此在 Oracle 解析器
 * 模式下（stmt->online_keyword = true）对分区表静默降级为普通构建。
 */
if (concurrent && partitioned && stmt->online_keyword)
    concurrent = false;