How to Bulk delete the document from solr without actually deleting the node?
I found the answer on exploring the apache solr module,

STEP 1

Select the nodes from the node table alone or by joining the apachesolr index entities table,

// Check for unpublished content that wasn't deleted from the index.
  $table = apachesolr_get_indexer_table('node');

 // Select the nids from the node table 
  $query = db_select($table, 'aien')
    -&gt;fields('aien', array('entity_id'))
    -&gt;condition('n.nid', 0);
  $query-&gt;leftJoin('node', 'n', 'n.nid = aien.entity_id');
  $nodes = $query-&gt;execute()-&gt;fetchAllAssoc('nid');


STEP 2

Chunk it to some limit and call the apachesolr_index_nodeapi_mass_delete function

      $node_lists = array_chunk($nodes, '100', TRUE);
  foreach ($node_lists as $nodes) {
    watchdog('Apache Solr', 'On cron running apachesolr_nodeapi_mass_delete() on nids @nids', array('@nids' =&gt; implode(',', array_keys($nodes))), WATCHDOG_WARNING);
    if (!apachesolr_index_nodeapi_mass_delete($nodes, $table)) {
      // Solr query failed - so stop trying.
      break;
    }
  }