Subject: Re: simplehash: preserve consistency in case of OOM

From: Andres Freund <[email-masked]>
Date: Fri, 17 Nov 2023 12:13:34 -0800

Hi,

On 2023-11-17 10:42:54 -0800, Jeff Davis wrote:
> Right now, if allocation fails while growing a hashtable, it's left in
> an inconsistent state and can't be used again.

I'm not against allowing this - but I am curious, in which use cases is this
useful?

> @@ -446,10 +459,11 @@ SH_CREATE(MemoryContext ctx, uint32 nelements, void *private_data)
>  	/* increase nelements by fillfactor, want to store nelements elements */
>  	size = Min((double) SH_MAX_SIZE, ((double) nelements) / SH_FILLFACTOR);
>  
> -	SH_COMPUTE_PARAMETERS(tb, size);
> +	size = SH_COMPUTE_SIZE(size);
>  
> -	tb->data = (SH_ELEMENT_TYPE *) SH_ALLOCATE(tb, sizeof(SH_ELEMENT_TYPE) * tb->size);
> +	tb->data = (SH_ELEMENT_TYPE *) SH_ALLOCATE(tb, sizeof(SH_ELEMENT_TYPE) * size);
>  
> +	SH_UPDATE_PARAMETERS(tb, size);
>  	return tb;
>  }

Maybe add a comment explaining why it's important to update parameters after
allocating?

Greetings,

Andres Freund