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One of my e-commerce sites with daily product uploads has sitemap listed has below. Recently we notice that google index rate has slowed down.
<url> <loc> http://urllink </loc> <lastmod>2016-07-22</lastmod> <changefreq>daily</changefreq> <priority>0.5</priority> </url>
Could it be because our automatically generated site map structured, wherein lastmod date is being shown as the previous date every day i.e. it tells google that this product has been changed the previous day when in fact it hasn't been. Does that mean Google will expend resources, try to see what has changed and if it hasn't changed it probably will starting assigning lower priority to our site and hence we run the risk of our more recently added products not being indexed.
We also have a feeling that this lastmod date error is probably eating a lot of our server resources too.
Hope that was clear. Thanks