PostgreSQL数据库事务系统Upper Layer——StartTransactionCommand

ゞ浴缸里的玫瑰 2022-09-15 11:51 181阅读 0赞

![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA6IKl5Y-U6I-M_size_20_color_FFFFFF_t_70_g_se_x_16]

StartTransactionCommand函数将事务块状态从TBLOCK\_DEFAULT改为TBLOCK\_STARTED，并调用底层函数StartTransaction。

void StartTransactionCommand(void) { 
    	TransactionState s = CurrentTransactionState;
    	switch (s->blockState) { 
    			/* if we aren't in a transaction block, we just do our usual start transaction. */
    		case TBLOCK_DEFAULT:
    			StartTransaction();
    			s->blockState = TBLOCK_STARTED;
    			break;
    			/* We are somewhere in a transaction block or subtransaction and about to start a new command. For now we do nothing, but someday we may do command-local resource initialization. (Note that any needed CommandCounterIncrement was done by the previous CommitTransactionCommand.) */
    		case TBLOCK_INPROGRESS:
    		case TBLOCK_IMPLICIT_INPROGRESS:
    		case TBLOCK_SUBINPROGRESS:
    			break;
    			/* Here we are in a failed transaction block (one of the commands caused an abort) so we do nothing but remain in the abort state. Eventually we will get a ROLLBACK command which will get us out of this state. (It is up to other code to ensure that no commands other than ROLLBACK will be processed in these states.) */
    		case TBLOCK_ABORT:
    		case TBLOCK_SUBABORT:
    			break;
    			/* These cases are invalid. */
    		case TBLOCK_STARTED:
    		case TBLOCK_BEGIN:
    		case TBLOCK_PARALLEL_INPROGRESS:
    		case TBLOCK_SUBBEGIN:
    		case TBLOCK_END:
    		case TBLOCK_SUBRELEASE:
    		case TBLOCK_SUBCOMMIT:
    		case TBLOCK_ABORT_END:
    		case TBLOCK_SUBABORT_END:
    		case TBLOCK_ABORT_PENDING:
    		case TBLOCK_SUBABORT_PENDING:
    		case TBLOCK_SUBRESTART:
    		case TBLOCK_SUBABORT_RESTART:
    		case TBLOCK_PREPARE:
    			elog(ERROR, "StartTransactionCommand: unexpected state %s", BlockStateAsString(s->blockState));
    			break;
    	}
    	/* We must switch to CurTransactionContext before returning. This is already done if we called StartTransaction, otherwise not. */
    	Assert(CurTransactionContext != NULL);
    	MemoryContextSwitchTo(CurTransactionContext);
    }

[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA6IKl5Y-U6I-M_size_20_color_FFFFFF_t_70_g_se_x_16]: /images/20220828/e1c945c83956410d80669abec3713834.png