Implement backfill in handler so we can do fetching later

Old and new implementation seem to perform the same :)

```
old implementation backfill events=[
  "event_id=$BU66ZRqOvMEH-wRgx3hruEBKH1tcUUD0rWdGnUEAcuQ,depth=11,body=Message 1 (eventIDsAfter),prevs=['$r7UcvfwqKAnhqAesYovjSEWaC4aOcXWJMWQ0W7LhBok']",
  "event_id=$r7UcvfwqKAnhqAesYovjSEWaC4aOcXWJMWQ0W7LhBok,depth=10,body=Message 0 (eventIDsAfter),prevs=['$9JuhSj0h0AbHvky0T3tSRfq_lxg1k2LTHY-J-MW6FfA']",
  "event_id=$jX7MRv7WeXx79_r44I45EC8peZ0eKgbN12wolz0_ueA,depth=10,body=org.matrix.msc2716.insertion,prevs=['$9JuhSj0h0AbHvky0T3tSRfq_lxg1k2LTHY-J-MW6FfA']",
  "event_id=$HG6XjFmFFO5O2-JW-kaayz2qJTwhzrtICjHdV9j0RMU,depth=10,body=org.matrix.msc2716.batch,prevs=['$d-z0eDSnU4PhbnisRLC7OIvoQFXlfnwhElh5mA1gFFo']",
  "event_id=$d-z0eDSnU4PhbnisRLC7OIvoQFXlfnwhElh5mA1gFFo,depth=10,body=Historical 99 (batch=0),prevs=['$z8iHeSZupiT5NOYzhhyOEFwrPMFI3vN2iDFpijniw6Q']",
  "event_id=$z8iHeSZupiT5NOYzhhyOEFwrPMFI3vN2iDFpijniw6Q,depth=10,body=Historical 98 (batch=0),prevs=['$ddn3uR4QbOH8imNzXy-_xz9Kn63qAJhC9NjFOUvu-_w']",
  "event_id=$ddn3uR4QbOH8imNzXy-_xz9Kn63qAJhC9NjFOUvu-_w,depth=10,body=Historical 97 (batch=0),prevs=['$BRTaYbuvXTnBpC-Dhee2UUBY-LePaWLTMd60sa82c_I']",
  "event_id=$BRTaYbuvXTnBpC-Dhee2UUBY-LePaWLTMd60sa82c_I,depth=10,body=Historical 96 (batch=0),prevs=['$HC1catch1Ti3NWcGWWXJ7doMinWfU-SNkCYJC7v_RxA']",
  "event_id=$HC1catch1Ti3NWcGWWXJ7doMinWfU-SNkCYJC7v_RxA,depth=10,body=Historical 95 (batch=0),prevs=['$DL3D99BYS_Cn047L6XxUvHN86icB69Yi9jttmxnepVo']",
  "event_id=$DL3D99BYS_Cn047L6XxUvHN86icB69Yi9jttmxnepVo,depth=10,body=Historical 94 (batch=0),prevs=['$bqDvvvMj2a4x4FUh_Iy6aA9sejqunlPQxjgDhM9-2CY']",
  "event_id=$bqDvvvMj2a4x4FUh_Iy6aA9sejqunlPQxjgDhM9-2CY,depth=10,body=Historical 93 (batch=0),prevs=['$CUhTzLqLabAzjqNbh9_SKSX1Re7z581D7BF90a3jE-0']",
  "event_id=$CUhTzLqLabAzjqNbh9_SKSX1Re7z581D7BF90a3jE-0,depth=10,body=Historical 92 (batch=0),prevs=['$3l6A4siERlLreAmXGH1KFagDjb9G8i4_TrxLErZS4FY']",
  "event_id=$3l6A4siERlLreAmXGH1KFagDjb9G8i4_TrxLErZS4FY,depth=10,body=Historical 91 (batch=0),prevs=['$BSosTk20sS031k33sDi_kMkrGMVjSUnCzT1wvZo0dcg']",
  "event_id=$BSosTk20sS031k33sDi_kMkrGMVjSUnCzT1wvZo0dcg,depth=10,body=Historical 90 (batch=0),prevs=['$XoyyYG9ngSu_sJ_npwDgrwLVQt0E6kDAxW_f0MzaIKs']",
  "event_id=$XoyyYG9ngSu_sJ_npwDgrwLVQt0E6kDAxW_f0MzaIKs,depth=10,body=Historical 89 (batch=0),prevs=['$8j7g564Kma7kqrgkqru2Nw21Ez2xZoyqBXtgrwYtbIU']",
  "event_id=$8j7g564Kma7kqrgkqru2Nw21Ez2xZoyqBXtgrwYtbIU,depth=10,body=Historical 88 (batch=0),prevs=['$FlIO19qRDZggQ3ZIMd4OhF4kGNpiipB4BR7sqQnG5xU']",
  "event_id=$FlIO19qRDZggQ3ZIMd4OhF4kGNpiipB4BR7sqQnG5xU,depth=10,body=Historical 87 (batch=0),prevs=['$reiGLF3R8Q5wqm_KJKOTQGFQ6PHIExRrV1nmB7lw5WA']",
  "event_id=$reiGLF3R8Q5wqm_KJKOTQGFQ6PHIExRrV1nmB7lw5WA,depth=10,body=Historical 86 (batch=0),prevs=['$7JRXCFtNfXY_TNZTZSjr7dPnKAMz39E8K2DQfhrxk0s']",
  "event_id=$7JRXCFtNfXY_TNZTZSjr7dPnKAMz39E8K2DQfhrxk0s,depth=10,body=Historical 85 (batch=0),prevs=['$8Z6-6uE22VHh3KoN2wGa9SAPhf0_MXPz3y_O2G8A9Bo']",
  "event_id=$8Z6-6uE22VHh3KoN2wGa9SAPhf0_MXPz3y_O2G8A9Bo,depth=10,body=Historical 84 (batch=0),prevs=['$CETAr2-SIsfT_exUgUY9El4PL6WOFnr7_6Hv86BuZUQ']",
  "event_id=$CETAr2-SIsfT_exUgUY9El4PL6WOFnr7_6Hv86BuZUQ,depth=10,body=Historical 83 (batch=0),prevs=['$dMOfVXcWxuoNS9di9AHyocIzAAucNG2v2aXqZWK7oA0']",
  "event_id=$dMOfVXcWxuoNS9di9AHyocIzAAucNG2v2aXqZWK7oA0,depth=10,body=Historical 82 (batch=0),prevs=['$4UjX4-4EejV7e0umXczxoqx9eHMvu2fFDIPGlY4zdrQ']",
  "event_id=$4UjX4-4EejV7e0umXczxoqx9eHMvu2fFDIPGlY4zdrQ,depth=10,body=Historical 81 (batch=0),prevs=['$e5d87r41P1lFrfM8iEp3waCi21lKx-bFBTEMhUMDJhE']",
  "event_id=$e5d87r41P1lFrfM8iEp3waCi21lKx-bFBTEMhUMDJhE,depth=10,body=Historical 80 (batch=0),prevs=['$ez0-Q4agOvUQbWUELiTJEEJWwZYj-TnaQTnNc3Vil8M']",
  "event_id=$ez0-Q4agOvUQbWUELiTJEEJWwZYj-TnaQTnNc3Vil8M,depth=10,body=Historical 79 (batch=0),prevs=['$zaMM-ZtQMADqFNsjrQrl_u0FIjxVHSEbdICkI5kph14']",
  "event_id=$zaMM-ZtQMADqFNsjrQrl_u0FIjxVHSEbdICkI5kph14,depth=10,body=Historical 78 (batch=0),prevs=['$jhDwZ4C8aCS7xm0D7xwQYKYXxE9yrnV_jnXWs7yj97A']",
  "event_id=$jhDwZ4C8aCS7xm0D7xwQYKYXxE9yrnV_jnXWs7yj97A,depth=10,body=Historical 77 (batch=0),prevs=['$794zi7lECGaZqgi-mVDTuAcCVxQRcasLEWHNQk_T5Qo']",
  "event_id=$794zi7lECGaZqgi-mVDTuAcCVxQRcasLEWHNQk_T5Qo,depth=10,body=Historical 76 (batch=0),prevs=['$RYc7Epu2beVamNOISGEPPzYPnqNr8OPpy6srKUDCNaY']",
  "event_id=$RYc7Epu2beVamNOISGEPPzYPnqNr8OPpy6srKUDCNaY,depth=10,body=Historical 75 (batch=0),prevs=['$NxzF542rsM0WMKZonV9YxmaJ5PLpVWK1TUfcLFP4VT8']",
  "event_id=$NxzF542rsM0WMKZonV9YxmaJ5PLpVWK1TUfcLFP4VT8,depth=10,body=Historical 74 (batch=0),prevs=['$YbcfMO7DOlq6owFILKIGpLSrvpMiDmIp77TCmafFxUU']",
  "event_id=$YbcfMO7DOlq6owFILKIGpLSrvpMiDmIp77TCmafFxUU,depth=10,body=Historical 73 (batch=0),prevs=['$RmlFFGojIl8VSc115lgQwk0NeAIAQT7CuLv3ajIv2X0']",
  "event_id=$RmlFFGojIl8VSc115lgQwk0NeAIAQT7CuLv3ajIv2X0,depth=10,body=Historical 72 (batch=0),prevs=['$lGGzpQOPdmzBqXIFF5HZfyGQCmXJOnmkZCRFRzxqJkw']",
  "event_id=$lGGzpQOPdmzBqXIFF5HZfyGQCmXJOnmkZCRFRzxqJkw,depth=10,body=Historical 71 (batch=0),prevs=['$TcSzi68MSFf1W0843Zi0iRq5vXFs8FhdtI9NfNCY5DM']",
  "event_id=$TcSzi68MSFf1W0843Zi0iRq5vXFs8FhdtI9NfNCY5DM,depth=10,body=Historical 70 (batch=0),prevs=['$iKaFgZ_aeN-ZJUNJEYj4WjY31RPm8PXs27n-u2LnlCE']",
  "event_id=$iKaFgZ_aeN-ZJUNJEYj4WjY31RPm8PXs27n-u2LnlCE,depth=10,body=Historical 69 (batch=0),prevs=['$n52R-hna5danKau87AHkwXDV5CuUTIZ960gtHr9X8hw']",
  "event_id=$n52R-hna5danKau87AHkwXDV5CuUTIZ960gtHr9X8hw,depth=10,body=Historical 68 (batch=0),prevs=['$Fr3wnWXII8LpE3VyF1pLWuLpSCyxu7jC1i4ggMqH1kE']",
  "event_id=$Fr3wnWXII8LpE3VyF1pLWuLpSCyxu7jC1i4ggMqH1kE,depth=10,body=Historical 67 (batch=0),prevs=['$ebCIN2TL4fFQeTEahzeX-VCkh_YEohAItvRd6LAVP2E']",
  "event_id=$ebCIN2TL4fFQeTEahzeX-VCkh_YEohAItvRd6LAVP2E,depth=10,body=Historical 66 (batch=0),prevs=['$CFeaKxHxgPCSUufJChertFT4au4P9Y1a_tTdN2wmo3Q']",
  "event_id=$CFeaKxHxgPCSUufJChertFT4au4P9Y1a_tTdN2wmo3Q,depth=10,body=Historical 65 (batch=0),prevs=['$MctpfuMG5AhhCb9aPRG-4V6VKxxNUzALNLq3BVJKejU']",
  "event_id=$MctpfuMG5AhhCb9aPRG-4V6VKxxNUzALNLq3BVJKejU,depth=10,body=Historical 64 (batch=0),prevs=['$ikjtTCZ7KXg1qtwgURuBZ-P5C1RG1oY8U3k2rm9RGxA']",
  "event_id=$ikjtTCZ7KXg1qtwgURuBZ-P5C1RG1oY8U3k2rm9RGxA,depth=10,body=Historical 63 (batch=0),prevs=['$KDbI-rBuoAI7rRhtAjcoDY2PbLQ9gDsK5fRts3OihSA']",
  "event_id=$KDbI-rBuoAI7rRhtAjcoDY2PbLQ9gDsK5fRts3OihSA,depth=10,body=Historical 62 (batch=0),prevs=['$_ZwqRJxNwgcZn4Trb5nrTjRP8ssQuLDq5ThguCm9KzE']",
  "event_id=$_ZwqRJxNwgcZn4Trb5nrTjRP8ssQuLDq5ThguCm9KzE,depth=10,body=Historical 61 (batch=0),prevs=['$hq1xDHEWodibkwlNg73931wjYlD5M29dkFHU0dQB2dk']",
  "event_id=$hq1xDHEWodibkwlNg73931wjYlD5M29dkFHU0dQB2dk,depth=10,body=Historical 60 (batch=0),prevs=['$XPRt_CuI_AXJylRQYbQ0ItkRkMy4ey0XxqS7iIdGLfQ']",
  "event_id=$XPRt_CuI_AXJylRQYbQ0ItkRkMy4ey0XxqS7iIdGLfQ,depth=10,body=Historical 59 (batch=0),prevs=['$Ucd44nYFkYVe_zs5wEqU5slG74IIPdzq_mqEHinIoIo']",
  "event_id=$Ucd44nYFkYVe_zs5wEqU5slG74IIPdzq_mqEHinIoIo,depth=10,body=Historical 58 (batch=0),prevs=['$CtM1TqWoFt3KabPNRKYi1vrpOPGwdpjx-15TpfKgYYA']",
  "event_id=$CtM1TqWoFt3KabPNRKYi1vrpOPGwdpjx-15TpfKgYYA,depth=10,body=Historical 57 (batch=0),prevs=['$Jo8T-m9nSs77uF4uFtkd22CifwnvDlr13Fs14NHcCMw']",
  "event_id=$Jo8T-m9nSs77uF4uFtkd22CifwnvDlr13Fs14NHcCMw,depth=10,body=Historical 56 (batch=0),prevs=['$WW45KevKriYRET0tOmKk8Ha9fFqxJJS_IC8Ih6I3L2A']",
  "event_id=$WW45KevKriYRET0tOmKk8Ha9fFqxJJS_IC8Ih6I3L2A,depth=10,body=Historical 55 (batch=0),prevs=['$G60oGyHZvp-Gim48qnC_epu2JRseKQUCTI5vqZEIbaI']",
  "event_id=$G60oGyHZvp-Gim48qnC_epu2JRseKQUCTI5vqZEIbaI,depth=10,body=Historical 54 (batch=0),prevs=['$R9Z6YaR1K9ulUzF9d6-ZL0QwJmwaEj1wTUPHrTJqFUs']",
  "event_id=$R9Z6YaR1K9ulUzF9d6-ZL0QwJmwaEj1wTUPHrTJqFUs,depth=10,body=Historical 53 (batch=0),prevs=['$CqedFlSaUBYWSHtkJJYmoc-DnxWCAaKVKOai0u5rawM']",
  "event_id=$CqedFlSaUBYWSHtkJJYmoc-DnxWCAaKVKOai0u5rawM,depth=10,body=Historical 52 (batch=0),prevs=['$3Ol33IgZ5lBuVwgELhRBYoFLb6GwkFTha3j6uxvHToY']",
  "event_id=$3Ol33IgZ5lBuVwgELhRBYoFLb6GwkFTha3j6uxvHToY,depth=10,body=Historical 51 (batch=0),prevs=['$wUcLTd2pGhliQunqWxFGvT6yiEZrUXA920-hcjaloSw']",
  "event_id=$wUcLTd2pGhliQunqWxFGvT6yiEZrUXA920-hcjaloSw,depth=10,body=Historical 50 (batch=0),prevs=['$gaO95ghwbwpGttuqBbhMrZJzz9Z440U7L2WOtDy7Hr8']",
  "event_id=$gaO95ghwbwpGttuqBbhMrZJzz9Z440U7L2WOtDy7Hr8,depth=10,body=Historical 49 (batch=0),prevs=['$4TSr_VvZzCV17JYxAob3DN2nQiYDqgW2S_QkW27v7Bg']",
  "event_id=$4TSr_VvZzCV17JYxAob3DN2nQiYDqgW2S_QkW27v7Bg,depth=10,body=Historical 48 (batch=0),prevs=['$bJaLResm_4aAwSjZ0POTvtVx4lnV9HKt8HwiYgP21lM']",
  "event_id=$bJaLResm_4aAwSjZ0POTvtVx4lnV9HKt8HwiYgP21lM,depth=10,body=Historical 47 (batch=0),prevs=['$BouN8LDmbFWiWo9Wc4wQi48YsC-icXewa05KR7byzhM']",
  "event_id=$BouN8LDmbFWiWo9Wc4wQi48YsC-icXewa05KR7byzhM,depth=10,body=Historical 46 (batch=0),prevs=['$n9Cv6EUu7i25OZLCllOE2PU4xjRthDKhkdtp5OtMuVk']",
  "event_id=$n9Cv6EUu7i25OZLCllOE2PU4xjRthDKhkdtp5OtMuVk,depth=10,body=Historical 45 (batch=0),prevs=['$MLVpmxVSSRRpxlcTkwIJT3neo7maqOp_ZLvwXRBY8A8']",
  "event_id=$MLVpmxVSSRRpxlcTkwIJT3neo7maqOp_ZLvwXRBY8A8,depth=10,body=Historical 44 (batch=0),prevs=['$tNv8Se5-lgfW-9MqE_upeBzq3QSPpsn7qOHz49WFs_c']",
  "event_id=$tNv8Se5-lgfW-9MqE_upeBzq3QSPpsn7qOHz49WFs_c,depth=10,body=Historical 43 (batch=0),prevs=['$XCDKybStk9PsquzrY-biUlKOmjk3wTXnsD1htiMdgAM']",
  "event_id=$XCDKybStk9PsquzrY-biUlKOmjk3wTXnsD1htiMdgAM,depth=10,body=Historical 42 (batch=0),prevs=['$iUDAE7nT6DQaNJSemwUpqQs8KvKTPFexcBJLTs2-gnY']",
  "event_id=$iUDAE7nT6DQaNJSemwUpqQs8KvKTPFexcBJLTs2-gnY,depth=10,body=Historical 41 (batch=0),prevs=['$T8NTrB9vQMLW-a0tT3corPl0g6O3UjGIoaHBjkjCD_w']",
  "event_id=$T8NTrB9vQMLW-a0tT3corPl0g6O3UjGIoaHBjkjCD_w,depth=10,body=Historical 40 (batch=0),prevs=['$N7jCLhKYDejMTejtrjJfM2lMRES5OPeowtvN-L4utsE']",
  "event_id=$N7jCLhKYDejMTejtrjJfM2lMRES5OPeowtvN-L4utsE,depth=10,body=Historical 39 (batch=0),prevs=['$Oy9aTfjL0LSnbF_6MRq7-5baaEbfxyRTK1kbVGeNoaU']",
  "event_id=$Oy9aTfjL0LSnbF_6MRq7-5baaEbfxyRTK1kbVGeNoaU,depth=10,body=Historical 38 (batch=0),prevs=['$V4qFDnqO1LrboSWwCoQpQ4dXLyrc74qZbbsaHxqAj4Q']",
  "event_id=$V4qFDnqO1LrboSWwCoQpQ4dXLyrc74qZbbsaHxqAj4Q,depth=10,body=Historical 37 (batch=0),prevs=['$vWdLNDGwj_mBJ6JZ2s01OhsxRuPNSSJAM_bMa6J9Q2c']",
  "event_id=$vWdLNDGwj_mBJ6JZ2s01OhsxRuPNSSJAM_bMa6J9Q2c,depth=10,body=Historical 36 (batch=0),prevs=['$JZt2EdPtKJX6f2MMbj_gSEseVAMa-H5r_J_yvfhHs5k']",
  "event_id=$JZt2EdPtKJX6f2MMbj_gSEseVAMa-H5r_J_yvfhHs5k,depth=10,body=Historical 35 (batch=0),prevs=['$NPzUfUgNfvkezhUeLmcp2utVA_XnW8YzDqbZlznsEN0']",
  "event_id=$NPzUfUgNfvkezhUeLmcp2utVA_XnW8YzDqbZlznsEN0,depth=10,body=Historical 34 (batch=0),prevs=['$NNUjzVtvOSFDYRID_PsMJrUC8gx5p1mPvIoMB7ibDn0']",
  "event_id=$NNUjzVtvOSFDYRID_PsMJrUC8gx5p1mPvIoMB7ibDn0,depth=10,body=Historical 33 (batch=0),prevs=['$dONbCTAYR0kOMVSmxOnM5aQ4bgx9PbKza98_e2Lxxw4']",
  "event_id=$dONbCTAYR0kOMVSmxOnM5aQ4bgx9PbKza98_e2Lxxw4,depth=10,body=Historical 32 (batch=0),prevs=['$dwxZHePgzbtQMO3caex0O9Zdl-gT3fpWRZD5dJ43JmE']",
  "event_id=$dwxZHePgzbtQMO3caex0O9Zdl-gT3fpWRZD5dJ43JmE,depth=10,body=Historical 31 (batch=0),prevs=['$5JOpa9222Y0__S8yfaZBT7ESuRaPeeRz80jleMoa5hE']",
  "event_id=$5JOpa9222Y0__S8yfaZBT7ESuRaPeeRz80jleMoa5hE,depth=10,body=Historical 30 (batch=0),prevs=['$7yIEFZZFs91wjKScsjbG854DUOqomPnV4iGG-EDWK6w']",
  "event_id=$7yIEFZZFs91wjKScsjbG854DUOqomPnV4iGG-EDWK6w,depth=10,body=Historical 29 (batch=0),prevs=['$9pzIrDRB1cuweDiHaPGB6AtTtGeGEOmqyoP59UAa0pI']",
  "event_id=$9pzIrDRB1cuweDiHaPGB6AtTtGeGEOmqyoP59UAa0pI,depth=10,body=Historical 28 (batch=0),prevs=['$EBu0Y6-OdqNUumOlHK__K2eXsN8mAYV21eCRKwGmkxU']",
  "event_id=$EBu0Y6-OdqNUumOlHK__K2eXsN8mAYV21eCRKwGmkxU,depth=10,body=Historical 27 (batch=0),prevs=['$95FzYeNZk31wyfaCojognGOAkzLhHLrv4_j3eoJawwU']",
  "event_id=$95FzYeNZk31wyfaCojognGOAkzLhHLrv4_j3eoJawwU,depth=10,body=Historical 26 (batch=0),prevs=['$QDGDnSNRXjNZG2lia2gjeD1aEfgfZ0gxI1BzIgjyZq8']",
  "event_id=$QDGDnSNRXjNZG2lia2gjeD1aEfgfZ0gxI1BzIgjyZq8,depth=10,body=Historical 25 (batch=0),prevs=['$tf1GB8ydPyNTNAaGwcTUXaTOSCmNohK6e6MmOnFwrJA']",
  "event_id=$tf1GB8ydPyNTNAaGwcTUXaTOSCmNohK6e6MmOnFwrJA,depth=10,body=Historical 24 (batch=0),prevs=['$n40ks3dofH6DioQlfe84n3exnYrboy8GHHYJ_qBFJMg']",
  "event_id=$n40ks3dofH6DioQlfe84n3exnYrboy8GHHYJ_qBFJMg,depth=10,body=Historical 23 (batch=0),prevs=['$xl8xG3MJiiNP21WNFmDLxOR8Rhy_FLws0snsmDUoAYQ']",
  "event_id=$xl8xG3MJiiNP21WNFmDLxOR8Rhy_FLws0snsmDUoAYQ,depth=10,body=Historical 22 (batch=0),prevs=['$6MxFONk8t5shoQpjjZyxd0ypmfj76LPs9hWKkPAxMcI']",
  "event_id=$6MxFONk8t5shoQpjjZyxd0ypmfj76LPs9hWKkPAxMcI,depth=10,body=Historical 21 (batch=0),prevs=['$XAAn4gMQe4ShIZKvZntEUBRljDM4IxHDVeNOXp3K2Bk']",
  "event_id=$XAAn4gMQe4ShIZKvZntEUBRljDM4IxHDVeNOXp3K2Bk,depth=10,body=Historical 20 (batch=0),prevs=['$Gj3RlKLUMb6hI_JyXdfwuoneWDs1b63qF7WdYYiNDG0']",
  "event_id=$Gj3RlKLUMb6hI_JyXdfwuoneWDs1b63qF7WdYYiNDG0,depth=10,body=Historical 19 (batch=0),prevs=['$yiRe3l3_APWuZt1wfFBxXQp2orQJZJvwv3yk4QNiPxo']",
  "event_id=$yiRe3l3_APWuZt1wfFBxXQp2orQJZJvwv3yk4QNiPxo,depth=10,body=Historical 18 (batch=0),prevs=['$v04Ud2zPqFe5M3jPbiLrqQ6r_QXgFlmRTMMLyVvAsN8']",
  "event_id=$v04Ud2zPqFe5M3jPbiLrqQ6r_QXgFlmRTMMLyVvAsN8,depth=10,body=Historical 17 (batch=0),prevs=['$tO5NiLH2mPBIMRVmrTIza6CUv7v6R0e_tgj0ZKEtpG0']",
  "event_id=$tO5NiLH2mPBIMRVmrTIza6CUv7v6R0e_tgj0ZKEtpG0,depth=10,body=Historical 16 (batch=0),prevs=['$fyQ-akREpz3vpQNqTZ47yxAs_APAw2L_bQ1iAudsPWk']",
  "event_id=$fyQ-akREpz3vpQNqTZ47yxAs_APAw2L_bQ1iAudsPWk,depth=10,body=Historical 15 (batch=0),prevs=['$qddW2HRZA0BudaIWuun6Odt6wDbz7ETRJmSY8wtjMnY']",
  "event_id=$qddW2HRZA0BudaIWuun6Odt6wDbz7ETRJmSY8wtjMnY,depth=10,body=Historical 14 (batch=0),prevs=['$fxl98r0B-sa2T8LDR2q6Wi01Zw6xCPZB5FcMf5x_vxI']",
  "event_id=$fxl98r0B-sa2T8LDR2q6Wi01Zw6xCPZB5FcMf5x_vxI,depth=10,body=Historical 13 (batch=0),prevs=['$1PML_QTo1MK_EuUz3OYyc2vDjfGKKYt-0sUSN9jTeHs']",
  "event_id=$1PML_QTo1MK_EuUz3OYyc2vDjfGKKYt-0sUSN9jTeHs,depth=10,body=Historical 12 (batch=0),prevs=['$YTz-q29BhUU_Ox7_CR7gao1v7mmMqLwbz51WWI0CjHs']",
  "event_id=$YTz-q29BhUU_Ox7_CR7gao1v7mmMqLwbz51WWI0CjHs,depth=10,body=Historical 11 (batch=0),prevs=['$Y3HUk4SiCWUrV5V_ZUcwC1IkVZEPM3V8oGWrWKRcv3I']",
  "event_id=$Y3HUk4SiCWUrV5V_ZUcwC1IkVZEPM3V8oGWrWKRcv3I,depth=10,body=Historical 10 (batch=0),prevs=['$uV5daep6tIdbImy2XEIxdQIuGYc547ulzxMplDyBWfY']",
  "event_id=$uV5daep6tIdbImy2XEIxdQIuGYc547ulzxMplDyBWfY,depth=10,body=Historical 9 (batch=0),prevs=['$bVKZ6uRROzC7aNcZc9cUsfhHl5dU_-Vm6Qz5V9X8GsI']",
  "event_id=$bVKZ6uRROzC7aNcZc9cUsfhHl5dU_-Vm6Qz5V9X8GsI,depth=10,body=Historical 8 (batch=0),prevs=['$6zjql7LGgIa3gFpf9owZsKWeFU4FoMUKDtVPpMo7xsM']",
  "event_id=$6zjql7LGgIa3gFpf9owZsKWeFU4FoMUKDtVPpMo7xsM,depth=10,body=Historical 7 (batch=0),prevs=['$w5t7UuOHrrsfZRebkX4adeEeJpPPGv9y6RyhKpxToMc']",
  "event_id=$w5t7UuOHrrsfZRebkX4adeEeJpPPGv9y6RyhKpxToMc,depth=10,body=Historical 6 (batch=0),prevs=['$649goNxH4B0DMta75_xs_TTib6C268A2JiUHvpUMu8g']",
  "event_id=$649goNxH4B0DMta75_xs_TTib6C268A2JiUHvpUMu8g,depth=10,body=Historical 5 (batch=0),prevs=['$mtUwpP0KSNwsn73yxBfQ7imKUe955v_SvI427PC5y2I']",
  "event_id=$9JuhSj0h0AbHvky0T3tSRfq_lxg1k2LTHY-J-MW6FfA,depth=9,body=Message 1 (eventIDsBefore),prevs=['$FcPmU5Fjg57eO_2J4VOK9jOcqRclEED5B9i1FsHNjaE']\"
]
```

```
new implementation backfill events=[
  "event_id=$BU66ZRqOvMEH-wRgx3hruEBKH1tcUUD0rWdGnUEAcuQ,depth=11,body=Message 1 (eventIDsAfter),prevs=['$r7UcvfwqKAnhqAesYovjSEWaC4aOcXWJMWQ0W7LhBok']",
  "event_id=$r7UcvfwqKAnhqAesYovjSEWaC4aOcXWJMWQ0W7LhBok,depth=10,body=Message 0 (eventIDsAfter),prevs=['$9JuhSj0h0AbHvky0T3tSRfq_lxg1k2LTHY-J-MW6FfA']",
  "event_id=$jX7MRv7WeXx79_r44I45EC8peZ0eKgbN12wolz0_ueA,depth=10,body=org.matrix.msc2716.insertion,prevs=['$9JuhSj0h0AbHvky0T3tSRfq_lxg1k2LTHY-J-MW6FfA']",
  "event_id=$HG6XjFmFFO5O2-JW-kaayz2qJTwhzrtICjHdV9j0RMU,depth=10,body=org.matrix.msc2716.batch,prevs=['$d-z0eDSnU4PhbnisRLC7OIvoQFXlfnwhElh5mA1gFFo']",
  "event_id=$d-z0eDSnU4PhbnisRLC7OIvoQFXlfnwhElh5mA1gFFo,depth=10,body=Historical 99 (batch=0),prevs=['$z8iHeSZupiT5NOYzhhyOEFwrPMFI3vN2iDFpijniw6Q']",
  "event_id=$z8iHeSZupiT5NOYzhhyOEFwrPMFI3vN2iDFpijniw6Q,depth=10,body=Historical 98 (batch=0),prevs=['$ddn3uR4QbOH8imNzXy-_xz9Kn63qAJhC9NjFOUvu-_w']",
  "event_id=$ddn3uR4QbOH8imNzXy-_xz9Kn63qAJhC9NjFOUvu-_w,depth=10,body=Historical 97 (batch=0),prevs=['$BRTaYbuvXTnBpC-Dhee2UUBY-LePaWLTMd60sa82c_I']",
  "event_id=$BRTaYbuvXTnBpC-Dhee2UUBY-LePaWLTMd60sa82c_I,depth=10,body=Historical 96 (batch=0),prevs=['$HC1catch1Ti3NWcGWWXJ7doMinWfU-SNkCYJC7v_RxA']",
  "event_id=$HC1catch1Ti3NWcGWWXJ7doMinWfU-SNkCYJC7v_RxA,depth=10,body=Historical 95 (batch=0),prevs=['$DL3D99BYS_Cn047L6XxUvHN86icB69Yi9jttmxnepVo']",
  "event_id=$DL3D99BYS_Cn047L6XxUvHN86icB69Yi9jttmxnepVo,depth=10,body=Historical 94 (batch=0),prevs=['$bqDvvvMj2a4x4FUh_Iy6aA9sejqunlPQxjgDhM9-2CY']",
  "event_id=$bqDvvvMj2a4x4FUh_Iy6aA9sejqunlPQxjgDhM9-2CY,depth=10,body=Historical 93 (batch=0),prevs=['$CUhTzLqLabAzjqNbh9_SKSX1Re7z581D7BF90a3jE-0']",
  "event_id=$CUhTzLqLabAzjqNbh9_SKSX1Re7z581D7BF90a3jE-0,depth=10,body=Historical 92 (batch=0),prevs=['$3l6A4siERlLreAmXGH1KFagDjb9G8i4_TrxLErZS4FY']",
  "event_id=$3l6A4siERlLreAmXGH1KFagDjb9G8i4_TrxLErZS4FY,depth=10,body=Historical 91 (batch=0),prevs=['$BSosTk20sS031k33sDi_kMkrGMVjSUnCzT1wvZo0dcg']",
  "event_id=$BSosTk20sS031k33sDi_kMkrGMVjSUnCzT1wvZo0dcg,depth=10,body=Historical 90 (batch=0),prevs=['$XoyyYG9ngSu_sJ_npwDgrwLVQt0E6kDAxW_f0MzaIKs']",
  "event_id=$XoyyYG9ngSu_sJ_npwDgrwLVQt0E6kDAxW_f0MzaIKs,depth=10,body=Historical 89 (batch=0),prevs=['$8j7g564Kma7kqrgkqru2Nw21Ez2xZoyqBXtgrwYtbIU']",
  "event_id=$8j7g564Kma7kqrgkqru2Nw21Ez2xZoyqBXtgrwYtbIU,depth=10,body=Historical 88 (batch=0),prevs=['$FlIO19qRDZggQ3ZIMd4OhF4kGNpiipB4BR7sqQnG5xU']",
  "event_id=$FlIO19qRDZggQ3ZIMd4OhF4kGNpiipB4BR7sqQnG5xU,depth=10,body=Historical 87 (batch=0),prevs=['$reiGLF3R8Q5wqm_KJKOTQGFQ6PHIExRrV1nmB7lw5WA']",
  "event_id=$reiGLF3R8Q5wqm_KJKOTQGFQ6PHIExRrV1nmB7lw5WA,depth=10,body=Historical 86 (batch=0),prevs=['$7JRXCFtNfXY_TNZTZSjr7dPnKAMz39E8K2DQfhrxk0s']",
  "event_id=$7JRXCFtNfXY_TNZTZSjr7dPnKAMz39E8K2DQfhrxk0s,depth=10,body=Historical 85 (batch=0),prevs=['$8Z6-6uE22VHh3KoN2wGa9SAPhf0_MXPz3y_O2G8A9Bo']",
  "event_id=$8Z6-6uE22VHh3KoN2wGa9SAPhf0_MXPz3y_O2G8A9Bo,depth=10,body=Historical 84 (batch=0),prevs=['$CETAr2-SIsfT_exUgUY9El4PL6WOFnr7_6Hv86BuZUQ']",
  "event_id=$CETAr2-SIsfT_exUgUY9El4PL6WOFnr7_6Hv86BuZUQ,depth=10,body=Historical 83 (batch=0),prevs=['$dMOfVXcWxuoNS9di9AHyocIzAAucNG2v2aXqZWK7oA0']",
  "event_id=$dMOfVXcWxuoNS9di9AHyocIzAAucNG2v2aXqZWK7oA0,depth=10,body=Historical 82 (batch=0),prevs=['$4UjX4-4EejV7e0umXczxoqx9eHMvu2fFDIPGlY4zdrQ']",
  "event_id=$4UjX4-4EejV7e0umXczxoqx9eHMvu2fFDIPGlY4zdrQ,depth=10,body=Historical 81 (batch=0),prevs=['$e5d87r41P1lFrfM8iEp3waCi21lKx-bFBTEMhUMDJhE']",
  "event_id=$e5d87r41P1lFrfM8iEp3waCi21lKx-bFBTEMhUMDJhE,depth=10,body=Historical 80 (batch=0),prevs=['$ez0-Q4agOvUQbWUELiTJEEJWwZYj-TnaQTnNc3Vil8M']",
  "event_id=$ez0-Q4agOvUQbWUELiTJEEJWwZYj-TnaQTnNc3Vil8M,depth=10,body=Historical 79 (batch=0),prevs=['$zaMM-ZtQMADqFNsjrQrl_u0FIjxVHSEbdICkI5kph14']",
  "event_id=$zaMM-ZtQMADqFNsjrQrl_u0FIjxVHSEbdICkI5kph14,depth=10,body=Historical 78 (batch=0),prevs=['$jhDwZ4C8aCS7xm0D7xwQYKYXxE9yrnV_jnXWs7yj97A']",
  "event_id=$jhDwZ4C8aCS7xm0D7xwQYKYXxE9yrnV_jnXWs7yj97A,depth=10,body=Historical 77 (batch=0),prevs=['$794zi7lECGaZqgi-mVDTuAcCVxQRcasLEWHNQk_T5Qo']",
  "event_id=$794zi7lECGaZqgi-mVDTuAcCVxQRcasLEWHNQk_T5Qo,depth=10,body=Historical 76 (batch=0),prevs=['$RYc7Epu2beVamNOISGEPPzYPnqNr8OPpy6srKUDCNaY']",
  "event_id=$RYc7Epu2beVamNOISGEPPzYPnqNr8OPpy6srKUDCNaY,depth=10,body=Historical 75 (batch=0),prevs=['$NxzF542rsM0WMKZonV9YxmaJ5PLpVWK1TUfcLFP4VT8']",
  "event_id=$NxzF542rsM0WMKZonV9YxmaJ5PLpVWK1TUfcLFP4VT8,depth=10,body=Historical 74 (batch=0),prevs=['$YbcfMO7DOlq6owFILKIGpLSrvpMiDmIp77TCmafFxUU']",
  "event_id=$YbcfMO7DOlq6owFILKIGpLSrvpMiDmIp77TCmafFxUU,depth=10,body=Historical 73 (batch=0),prevs=['$RmlFFGojIl8VSc115lgQwk0NeAIAQT7CuLv3ajIv2X0']",
  "event_id=$RmlFFGojIl8VSc115lgQwk0NeAIAQT7CuLv3ajIv2X0,depth=10,body=Historical 72 (batch=0),prevs=['$lGGzpQOPdmzBqXIFF5HZfyGQCmXJOnmkZCRFRzxqJkw']",
  "event_id=$lGGzpQOPdmzBqXIFF5HZfyGQCmXJOnmkZCRFRzxqJkw,depth=10,body=Historical 71 (batch=0),prevs=['$TcSzi68MSFf1W0843Zi0iRq5vXFs8FhdtI9NfNCY5DM']",
  "event_id=$TcSzi68MSFf1W0843Zi0iRq5vXFs8FhdtI9NfNCY5DM,depth=10,body=Historical 70 (batch=0),prevs=['$iKaFgZ_aeN-ZJUNJEYj4WjY31RPm8PXs27n-u2LnlCE']",
  "event_id=$iKaFgZ_aeN-ZJUNJEYj4WjY31RPm8PXs27n-u2LnlCE,depth=10,body=Historical 69 (batch=0),prevs=['$n52R-hna5danKau87AHkwXDV5CuUTIZ960gtHr9X8hw']",
  "event_id=$n52R-hna5danKau87AHkwXDV5CuUTIZ960gtHr9X8hw,depth=10,body=Historical 68 (batch=0),prevs=['$Fr3wnWXII8LpE3VyF1pLWuLpSCyxu7jC1i4ggMqH1kE']",
  "event_id=$Fr3wnWXII8LpE3VyF1pLWuLpSCyxu7jC1i4ggMqH1kE,depth=10,body=Historical 67 (batch=0),prevs=['$ebCIN2TL4fFQeTEahzeX-VCkh_YEohAItvRd6LAVP2E']",
  "event_id=$ebCIN2TL4fFQeTEahzeX-VCkh_YEohAItvRd6LAVP2E,depth=10,body=Historical 66 (batch=0),prevs=['$CFeaKxHxgPCSUufJChertFT4au4P9Y1a_tTdN2wmo3Q']",
  "event_id=$CFeaKxHxgPCSUufJChertFT4au4P9Y1a_tTdN2wmo3Q,depth=10,body=Historical 65 (batch=0),prevs=['$MctpfuMG5AhhCb9aPRG-4V6VKxxNUzALNLq3BVJKejU']",
  "event_id=$MctpfuMG5AhhCb9aPRG-4V6VKxxNUzALNLq3BVJKejU,depth=10,body=Historical 64 (batch=0),prevs=['$ikjtTCZ7KXg1qtwgURuBZ-P5C1RG1oY8U3k2rm9RGxA']",
  "event_id=$ikjtTCZ7KXg1qtwgURuBZ-P5C1RG1oY8U3k2rm9RGxA,depth=10,body=Historical 63 (batch=0),prevs=['$KDbI-rBuoAI7rRhtAjcoDY2PbLQ9gDsK5fRts3OihSA']",
  "event_id=$KDbI-rBuoAI7rRhtAjcoDY2PbLQ9gDsK5fRts3OihSA,depth=10,body=Historical 62 (batch=0),prevs=['$_ZwqRJxNwgcZn4Trb5nrTjRP8ssQuLDq5ThguCm9KzE']",
  "event_id=$_ZwqRJxNwgcZn4Trb5nrTjRP8ssQuLDq5ThguCm9KzE,depth=10,body=Historical 61 (batch=0),prevs=['$hq1xDHEWodibkwlNg73931wjYlD5M29dkFHU0dQB2dk']",
  "event_id=$hq1xDHEWodibkwlNg73931wjYlD5M29dkFHU0dQB2dk,depth=10,body=Historical 60 (batch=0),prevs=['$XPRt_CuI_AXJylRQYbQ0ItkRkMy4ey0XxqS7iIdGLfQ']",
  "event_id=$XPRt_CuI_AXJylRQYbQ0ItkRkMy4ey0XxqS7iIdGLfQ,depth=10,body=Historical 59 (batch=0),prevs=['$Ucd44nYFkYVe_zs5wEqU5slG74IIPdzq_mqEHinIoIo']",
  "event_id=$Ucd44nYFkYVe_zs5wEqU5slG74IIPdzq_mqEHinIoIo,depth=10,body=Historical 58 (batch=0),prevs=['$CtM1TqWoFt3KabPNRKYi1vrpOPGwdpjx-15TpfKgYYA']",
  "event_id=$CtM1TqWoFt3KabPNRKYi1vrpOPGwdpjx-15TpfKgYYA,depth=10,body=Historical 57 (batch=0),prevs=['$Jo8T-m9nSs77uF4uFtkd22CifwnvDlr13Fs14NHcCMw']",
  "event_id=$Jo8T-m9nSs77uF4uFtkd22CifwnvDlr13Fs14NHcCMw,depth=10,body=Historical 56 (batch=0),prevs=['$WW45KevKriYRET0tOmKk8Ha9fFqxJJS_IC8Ih6I3L2A']",
  "event_id=$WW45KevKriYRET0tOmKk8Ha9fFqxJJS_IC8Ih6I3L2A,depth=10,body=Historical 55 (batch=0),prevs=['$G60oGyHZvp-Gim48qnC_epu2JRseKQUCTI5vqZEIbaI']",
  "event_id=$G60oGyHZvp-Gim48qnC_epu2JRseKQUCTI5vqZEIbaI,depth=10,body=Historical 54 (batch=0),prevs=['$R9Z6YaR1K9ulUzF9d6-ZL0QwJmwaEj1wTUPHrTJqFUs']",
  "event_id=$R9Z6YaR1K9ulUzF9d6-ZL0QwJmwaEj1wTUPHrTJqFUs,depth=10,body=Historical 53 (batch=0),prevs=['$CqedFlSaUBYWSHtkJJYmoc-DnxWCAaKVKOai0u5rawM']",
  "event_id=$CqedFlSaUBYWSHtkJJYmoc-DnxWCAaKVKOai0u5rawM,depth=10,body=Historical 52 (batch=0),prevs=['$3Ol33IgZ5lBuVwgELhRBYoFLb6GwkFTha3j6uxvHToY']",
  "event_id=$3Ol33IgZ5lBuVwgELhRBYoFLb6GwkFTha3j6uxvHToY,depth=10,body=Historical 51 (batch=0),prevs=['$wUcLTd2pGhliQunqWxFGvT6yiEZrUXA920-hcjaloSw']",
  "event_id=$wUcLTd2pGhliQunqWxFGvT6yiEZrUXA920-hcjaloSw,depth=10,body=Historical 50 (batch=0),prevs=['$gaO95ghwbwpGttuqBbhMrZJzz9Z440U7L2WOtDy7Hr8']",
  "event_id=$gaO95ghwbwpGttuqBbhMrZJzz9Z440U7L2WOtDy7Hr8,depth=10,body=Historical 49 (batch=0),prevs=['$4TSr_VvZzCV17JYxAob3DN2nQiYDqgW2S_QkW27v7Bg']",
  "event_id=$4TSr_VvZzCV17JYxAob3DN2nQiYDqgW2S_QkW27v7Bg,depth=10,body=Historical 48 (batch=0),prevs=['$bJaLResm_4aAwSjZ0POTvtVx4lnV9HKt8HwiYgP21lM']",
  "event_id=$bJaLResm_4aAwSjZ0POTvtVx4lnV9HKt8HwiYgP21lM,depth=10,body=Historical 47 (batch=0),prevs=['$BouN8LDmbFWiWo9Wc4wQi48YsC-icXewa05KR7byzhM']",
  "event_id=$BouN8LDmbFWiWo9Wc4wQi48YsC-icXewa05KR7byzhM,depth=10,body=Historical 46 (batch=0),prevs=['$n9Cv6EUu7i25OZLCllOE2PU4xjRthDKhkdtp5OtMuVk']",
  "event_id=$n9Cv6EUu7i25OZLCllOE2PU4xjRthDKhkdtp5OtMuVk,depth=10,body=Historical 45 (batch=0),prevs=['$MLVpmxVSSRRpxlcTkwIJT3neo7maqOp_ZLvwXRBY8A8']",
  "event_id=$MLVpmxVSSRRpxlcTkwIJT3neo7maqOp_ZLvwXRBY8A8,depth=10,body=Historical 44 (batch=0),prevs=['$tNv8Se5-lgfW-9MqE_upeBzq3QSPpsn7qOHz49WFs_c']",
  "event_id=$tNv8Se5-lgfW-9MqE_upeBzq3QSPpsn7qOHz49WFs_c,depth=10,body=Historical 43 (batch=0),prevs=['$XCDKybStk9PsquzrY-biUlKOmjk3wTXnsD1htiMdgAM']",
  "event_id=$XCDKybStk9PsquzrY-biUlKOmjk3wTXnsD1htiMdgAM,depth=10,body=Historical 42 (batch=0),prevs=['$iUDAE7nT6DQaNJSemwUpqQs8KvKTPFexcBJLTs2-gnY']",
  "event_id=$iUDAE7nT6DQaNJSemwUpqQs8KvKTPFexcBJLTs2-gnY,depth=10,body=Historical 41 (batch=0),prevs=['$T8NTrB9vQMLW-a0tT3corPl0g6O3UjGIoaHBjkjCD_w']",
  "event_id=$T8NTrB9vQMLW-a0tT3corPl0g6O3UjGIoaHBjkjCD_w,depth=10,body=Historical 40 (batch=0),prevs=['$N7jCLhKYDejMTejtrjJfM2lMRES5OPeowtvN-L4utsE']",
  "event_id=$N7jCLhKYDejMTejtrjJfM2lMRES5OPeowtvN-L4utsE,depth=10,body=Historical 39 (batch=0),prevs=['$Oy9aTfjL0LSnbF_6MRq7-5baaEbfxyRTK1kbVGeNoaU']",
  "event_id=$Oy9aTfjL0LSnbF_6MRq7-5baaEbfxyRTK1kbVGeNoaU,depth=10,body=Historical 38 (batch=0),prevs=['$V4qFDnqO1LrboSWwCoQpQ4dXLyrc74qZbbsaHxqAj4Q']",
  "event_id=$V4qFDnqO1LrboSWwCoQpQ4dXLyrc74qZbbsaHxqAj4Q,depth=10,body=Historical 37 (batch=0),prevs=['$vWdLNDGwj_mBJ6JZ2s01OhsxRuPNSSJAM_bMa6J9Q2c']",
  "event_id=$vWdLNDGwj_mBJ6JZ2s01OhsxRuPNSSJAM_bMa6J9Q2c,depth=10,body=Historical 36 (batch=0),prevs=['$JZt2EdPtKJX6f2MMbj_gSEseVAMa-H5r_J_yvfhHs5k']",
  "event_id=$JZt2EdPtKJX6f2MMbj_gSEseVAMa-H5r_J_yvfhHs5k,depth=10,body=Historical 35 (batch=0),prevs=['$NPzUfUgNfvkezhUeLmcp2utVA_XnW8YzDqbZlznsEN0']",
  "event_id=$NPzUfUgNfvkezhUeLmcp2utVA_XnW8YzDqbZlznsEN0,depth=10,body=Historical 34 (batch=0),prevs=['$NNUjzVtvOSFDYRID_PsMJrUC8gx5p1mPvIoMB7ibDn0']",
  "event_id=$NNUjzVtvOSFDYRID_PsMJrUC8gx5p1mPvIoMB7ibDn0,depth=10,body=Historical 33 (batch=0),prevs=['$dONbCTAYR0kOMVSmxOnM5aQ4bgx9PbKza98_e2Lxxw4']",
  "event_id=$dONbCTAYR0kOMVSmxOnM5aQ4bgx9PbKza98_e2Lxxw4,depth=10,body=Historical 32 (batch=0),prevs=['$dwxZHePgzbtQMO3caex0O9Zdl-gT3fpWRZD5dJ43JmE']",
  "event_id=$dwxZHePgzbtQMO3caex0O9Zdl-gT3fpWRZD5dJ43JmE,depth=10,body=Historical 31 (batch=0),prevs=['$5JOpa9222Y0__S8yfaZBT7ESuRaPeeRz80jleMoa5hE']",
  "event_id=$5JOpa9222Y0__S8yfaZBT7ESuRaPeeRz80jleMoa5hE,depth=10,body=Historical 30 (batch=0),prevs=['$7yIEFZZFs91wjKScsjbG854DUOqomPnV4iGG-EDWK6w']",
  "event_id=$7yIEFZZFs91wjKScsjbG854DUOqomPnV4iGG-EDWK6w,depth=10,body=Historical 29 (batch=0),prevs=['$9pzIrDRB1cuweDiHaPGB6AtTtGeGEOmqyoP59UAa0pI']",
  "event_id=$9pzIrDRB1cuweDiHaPGB6AtTtGeGEOmqyoP59UAa0pI,depth=10,body=Historical 28 (batch=0),prevs=['$EBu0Y6-OdqNUumOlHK__K2eXsN8mAYV21eCRKwGmkxU']",
  "event_id=$EBu0Y6-OdqNUumOlHK__K2eXsN8mAYV21eCRKwGmkxU,depth=10,body=Historical 27 (batch=0),prevs=['$95FzYeNZk31wyfaCojognGOAkzLhHLrv4_j3eoJawwU']",
  "event_id=$95FzYeNZk31wyfaCojognGOAkzLhHLrv4_j3eoJawwU,depth=10,body=Historical 26 (batch=0),prevs=['$QDGDnSNRXjNZG2lia2gjeD1aEfgfZ0gxI1BzIgjyZq8']",
  "event_id=$QDGDnSNRXjNZG2lia2gjeD1aEfgfZ0gxI1BzIgjyZq8,depth=10,body=Historical 25 (batch=0),prevs=['$tf1GB8ydPyNTNAaGwcTUXaTOSCmNohK6e6MmOnFwrJA']",
  "event_id=$tf1GB8ydPyNTNAaGwcTUXaTOSCmNohK6e6MmOnFwrJA,depth=10,body=Historical 24 (batch=0),prevs=['$n40ks3dofH6DioQlfe84n3exnYrboy8GHHYJ_qBFJMg']",
  "event_id=$n40ks3dofH6DioQlfe84n3exnYrboy8GHHYJ_qBFJMg,depth=10,body=Historical 23 (batch=0),prevs=['$xl8xG3MJiiNP21WNFmDLxOR8Rhy_FLws0snsmDUoAYQ']",
  "event_id=$xl8xG3MJiiNP21WNFmDLxOR8Rhy_FLws0snsmDUoAYQ,depth=10,body=Historical 22 (batch=0),prevs=['$6MxFONk8t5shoQpjjZyxd0ypmfj76LPs9hWKkPAxMcI']",
  "event_id=$6MxFONk8t5shoQpjjZyxd0ypmfj76LPs9hWKkPAxMcI,depth=10,body=Historical 21 (batch=0),prevs=['$XAAn4gMQe4ShIZKvZntEUBRljDM4IxHDVeNOXp3K2Bk']",
  "event_id=$XAAn4gMQe4ShIZKvZntEUBRljDM4IxHDVeNOXp3K2Bk,depth=10,body=Historical 20 (batch=0),prevs=['$Gj3RlKLUMb6hI_JyXdfwuoneWDs1b63qF7WdYYiNDG0']",
  "event_id=$Gj3RlKLUMb6hI_JyXdfwuoneWDs1b63qF7WdYYiNDG0,depth=10,body=Historical 19 (batch=0),prevs=['$yiRe3l3_APWuZt1wfFBxXQp2orQJZJvwv3yk4QNiPxo']",
  "event_id=$yiRe3l3_APWuZt1wfFBxXQp2orQJZJvwv3yk4QNiPxo,depth=10,body=Historical 18 (batch=0),prevs=['$v04Ud2zPqFe5M3jPbiLrqQ6r_QXgFlmRTMMLyVvAsN8']",
  "event_id=$v04Ud2zPqFe5M3jPbiLrqQ6r_QXgFlmRTMMLyVvAsN8,depth=10,body=Historical 17 (batch=0),prevs=['$tO5NiLH2mPBIMRVmrTIza6CUv7v6R0e_tgj0ZKEtpG0']",
  "event_id=$tO5NiLH2mPBIMRVmrTIza6CUv7v6R0e_tgj0ZKEtpG0,depth=10,body=Historical 16 (batch=0),prevs=['$fyQ-akREpz3vpQNqTZ47yxAs_APAw2L_bQ1iAudsPWk']",
  "event_id=$fyQ-akREpz3vpQNqTZ47yxAs_APAw2L_bQ1iAudsPWk,depth=10,body=Historical 15 (batch=0),prevs=['$qddW2HRZA0BudaIWuun6Odt6wDbz7ETRJmSY8wtjMnY']",
  "event_id=$qddW2HRZA0BudaIWuun6Odt6wDbz7ETRJmSY8wtjMnY,depth=10,body=Historical 14 (batch=0),prevs=['$fxl98r0B-sa2T8LDR2q6Wi01Zw6xCPZB5FcMf5x_vxI']",
  "event_id=$fxl98r0B-sa2T8LDR2q6Wi01Zw6xCPZB5FcMf5x_vxI,depth=10,body=Historical 13 (batch=0),prevs=['$1PML_QTo1MK_EuUz3OYyc2vDjfGKKYt-0sUSN9jTeHs']",
  "event_id=$1PML_QTo1MK_EuUz3OYyc2vDjfGKKYt-0sUSN9jTeHs,depth=10,body=Historical 12 (batch=0),prevs=['$YTz-q29BhUU_Ox7_CR7gao1v7mmMqLwbz51WWI0CjHs']",
  "event_id=$YTz-q29BhUU_Ox7_CR7gao1v7mmMqLwbz51WWI0CjHs,depth=10,body=Historical 11 (batch=0),prevs=['$Y3HUk4SiCWUrV5V_ZUcwC1IkVZEPM3V8oGWrWKRcv3I']",
  "event_id=$Y3HUk4SiCWUrV5V_ZUcwC1IkVZEPM3V8oGWrWKRcv3I,depth=10,body=Historical 10 (batch=0),prevs=['$uV5daep6tIdbImy2XEIxdQIuGYc547ulzxMplDyBWfY']",
  "event_id=$uV5daep6tIdbImy2XEIxdQIuGYc547ulzxMplDyBWfY,depth=10,body=Historical 9 (batch=0),prevs=['$bVKZ6uRROzC7aNcZc9cUsfhHl5dU_-Vm6Qz5V9X8GsI']",
  "event_id=$bVKZ6uRROzC7aNcZc9cUsfhHl5dU_-Vm6Qz5V9X8GsI,depth=10,body=Historical 8 (batch=0),prevs=['$6zjql7LGgIa3gFpf9owZsKWeFU4FoMUKDtVPpMo7xsM']",
  "event_id=$6zjql7LGgIa3gFpf9owZsKWeFU4FoMUKDtVPpMo7xsM,depth=10,body=Historical 7 (batch=0),prevs=['$w5t7UuOHrrsfZRebkX4adeEeJpPPGv9y6RyhKpxToMc']",
  "event_id=$w5t7UuOHrrsfZRebkX4adeEeJpPPGv9y6RyhKpxToMc,depth=10,body=Historical 6 (batch=0),prevs=['$649goNxH4B0DMta75_xs_TTib6C268A2JiUHvpUMu8g']",
  "event_id=$649goNxH4B0DMta75_xs_TTib6C268A2JiUHvpUMu8g,depth=10,body=Historical 5 (batch=0),prevs=['$mtUwpP0KSNwsn73yxBfQ7imKUe955v_SvI427PC5y2I']",
  "event_id=$9JuhSj0h0AbHvky0T3tSRfq_lxg1k2LTHY-J-MW6FfA,depth=9,body=Message 1 (eventIDsBefore),prevs=['$FcPmU5Fjg57eO_2J4VOK9jOcqRclEED5B9i1FsHNjaE']"
]
```

3 files changed, 321 insertions, 44 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py

index c478e0bc5c..e28c74daf0 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -16,6 +16,7 @@
 """Contains handlers for federation events."""
 
 import logging
+from queue import Empty, PriorityQueue
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Tuple, Union
 
@@ -1041,6 +1042,135 @@ class FederationHandler:
         else:
             return []
 
+    async def get_backfill_events(
+        self, room_id: str, event_id_list: list, limit: int
+    ) -> List[EventBase]:
+        event_id_results = set()
+
+        # In a PriorityQueue, the lowest valued entries are retrieved first.
+        # We're using depth as the priority in the queue and tie-break based on
+        # stream_ordering. Depth is lowest at the oldest-in-time message and
+        # highest and newest-in-time message. We add events to the queue with a
+        # negative depth so that we process the newest-in-time messages first
+        # going backwards in time. stream_ordering follows the same pattern.
+        queue = PriorityQueue()
+
+        seed_events = await self.store.get_events_as_list(event_id_list)
+        for seed_event in seed_events:
+            # Make sure the seed event actually pertains to this room. We also
+            # need to make sure the depth is available since our whole DAG
+            # navigation here depends on depth.
+            if seed_event.room_id == room_id and seed_event.depth:
+                queue.put(
+                    (
+                        -seed_event.depth,
+                        -seed_event.internal_metadata.stream_ordering,
+                        seed_event.event_id,
+                        seed_event.type,
+                    )
+                )
+
+        while not queue.empty() and len(event_id_results) < limit:
+            try:
+                _, _, event_id, event_type = queue.get_nowait()
+            except Empty:
+                break
+
+            if event_id in event_id_results:
+                continue
+
+            event_id_results.add(event_id)
+
+            if self.hs.config.experimental.msc2716_enabled:
+                # Try and find any potential historical batches of message history.
+                #
+                # First we look for an insertion event connected to the current
+                # event (by prev_event). If we find any, we'll add them to the queue
+                # and navigate up the DAG like normal in the next iteration of the
+                # loop.
+                connected_insertion_event_backfill_results = (
+                    await self.store.get_connected_insertion_event_backfill_results(
+                        event_id, limit - len(event_id_results)
+                    )
+                )
+                logger.debug(
+                    "_get_backfill_events: connected_insertion_event_backfill_results=%s",
+                    connected_insertion_event_backfill_results,
+                )
+                for (
+                    connected_insertion_event_backfill_item
+                ) in connected_insertion_event_backfill_results:
+                    if (
+                        connected_insertion_event_backfill_item.event_id
+                        not in event_id_results
+                    ):
+                        queue.put(
+                            (
+                                -connected_insertion_event_backfill_item.depth,
+                                -connected_insertion_event_backfill_item.stream_ordering,
+                                connected_insertion_event_backfill_item.event_id,
+                                connected_insertion_event_backfill_item.type,
+                            )
+                        )
+
+                # Second, we need to go and try to find any batch events connected
+                # to a given insertion event (by batch_id). If we find any, we'll
+                # add them to the queue and navigate up the DAG like normal in the
+                # next iteration of the loop.
+                if event_type == EventTypes.MSC2716_INSERTION:
+                    connected_batch_event_backfill_results = (
+                        await self.store.get_connected_batch_event_backfill_results(
+                            event_id, limit - len(event_id_results)
+                        )
+                    )
+                    logger.debug(
+                        "_get_backfill_events: connected_batch_event_backfill_results %s",
+                        connected_batch_event_backfill_results,
+                    )
+                    for (
+                        connected_batch_event_backfill_item
+                    ) in connected_batch_event_backfill_results:
+                        if (
+                            connected_batch_event_backfill_item.event_id
+                            not in event_id_results
+                        ):
+                            queue.put(
+                                (
+                                    -connected_batch_event_backfill_item.depth,
+                                    -connected_batch_event_backfill_item.stream_ordering,
+                                    connected_batch_event_backfill_item.event_id,
+                                    connected_batch_event_backfill_item.type,
+                                )
+                            )
+
+            # Now we just look up the DAG by prev_events as normal
+            connected_prev_event_backfill_results = (
+                await self.store.get_connected_prev_event_backfill_results(
+                    event_id, limit - len(event_id_results)
+                )
+            )
+            logger.debug(
+                "_get_backfill_events: prev_event_ids %s",
+                connected_prev_event_backfill_results,
+            )
+            for (
+                connected_prev_event_backfill_item
+            ) in connected_prev_event_backfill_results:
+                if connected_prev_event_backfill_item.event_id not in event_id_results:
+                    queue.put(
+                        (
+                            -connected_prev_event_backfill_item.depth,
+                            -connected_prev_event_backfill_item.stream_ordering,
+                            connected_prev_event_backfill_item.event_id,
+                            connected_prev_event_backfill_item.type,
+                        )
+                    )
+
+        events = await self.store.get_events_as_list(event_id_results)
+        return sorted(
+            events, key=lambda e: (-e.depth, -e.internal_metadata.stream_ordering)
+        )
+
     @log_function
     async def on_backfill_request(
         self, origin: str, room_id: str, pdu_list: List[str], limit: int
@@ -1053,6 +1183,34 @@ class FederationHandler:
         limit = min(limit, 100)
 
         events = await self.store.get_backfill_events(room_id, pdu_list, limit)
+        logger.info(
+            "old implementation backfill events=%s",
+            [
+                "event_id=%s,depth=%d,body=%s,prevs=%s\n"
+                % (
+                    event.event_id,
+                    event.depth,
+                    event.content.get("body", event.type),
+                    event.prev_event_ids(),
+                )
+                for event in events
+            ],
+        )
+
+        events = await self.get_backfill_events(room_id, pdu_list, limit)
+        logger.info(
+            "new implementation backfill events=%s",
+            [
+                "event_id=%s,depth=%d,body=%s,prevs=%s\n"
+                % (
+                    event.event_id,
+                    event.depth,
+                    event.content.get("body", event.type),
+                    event.prev_event_ids(),
+                )
+                for event in events
+            ],
+        )
 
         events = await filter_events_for_server(self.storage, origin, events)
 
diff --git a/synapse/handlers/federation_event.py b/synapse/handlers/federation_event.py

index ab2ed53bce..c9060a594f 100644
--- a/synapse/handlers/federation_event.py
+++ b/synapse/handlers/federation_event.py
@@ -702,38 +702,38 @@ class FederationEventHandler:
                         event.event_id
                     )
 
-                    # Maybe we can get lucky and save ourselves a lookup
-                    # by checking the events in the backfill first
-                    insertion_event = event_map[
-                        insertion_event_id
-                    ] or await self._store.get_event(
-                        insertion_event_id, allow_none=True
-                    )
-
-                    if insertion_event:
-                        # Connect the insertion events' `prev_event` successors
-                        # via fake edges pointing to the insertion event itself
-                        # so the insertion event sorts topologically
-                        # behind-in-time the successor. Nestled perfectly
-                        # between the prev_event and the successor.
-                        for insertion_prev_event_id in insertion_event.prev_event_ids():
-                            successor_event_ids = successor_event_id_map[
-                                insertion_prev_event_id
-                            ]
-                            logger.info(
-                                "insertion_event_id=%s successor_event_ids=%s",
-                                insertion_event_id,
-                                successor_event_ids,
-                            )
-                            if successor_event_ids:
-                                for successor_event_id in successor_event_ids:
-                                    # Don't add itself back as a successor
-                                    if successor_event_id != insertion_event_id:
-                                        # Fake edge to point the successor back
-                                        # at the insertion event
-                                        event_id_graph.setdefault(
-                                            successor_event_id, []
-                                        ).append(insertion_event_id)
+                    # # Maybe we can get lucky and save ourselves a lookup
+                    # # by checking the events in the backfill first
+                    # insertion_event = event_map[
+                    #     insertion_event_id
+                    # ] or await self._store.get_event(
+                    #     insertion_event_id, allow_none=True
+                    # )
+
+                    # if insertion_event:
+                    #     # Connect the insertion events' `prev_event` successors
+                    #     # via fake edges pointing to the insertion event itself
+                    #     # so the insertion event sorts topologically
+                    #     # behind-in-time the successor. Nestled perfectly
+                    #     # between the prev_event and the successor.
+                    #     for insertion_prev_event_id in insertion_event.prev_event_ids():
+                    #         successor_event_ids = successor_event_id_map[
+                    #             insertion_prev_event_id
+                    #         ]
+                    #         logger.info(
+                    #             "insertion_event_id=%s successor_event_ids=%s",
+                    #             insertion_event_id,
+                    #             successor_event_ids,
+                    #         )
+                    #         if successor_event_ids:
+                    #             for successor_event_id in successor_event_ids:
+                    #                 # Don't add itself back as a successor
+                    #                 if successor_event_id != insertion_event_id:
+                    #                     # Fake edge to point the successor back
+                    #                     # at the insertion event
+                    #                     event_id_graph.setdefault(
+                    #                         successor_event_id, []
+                    #                     ).append(insertion_event_id)
 
         # TODO: We also need to add fake edges to connect the oldest-in-time messages
         # in the batch to the event we branched off of, see https://github.com/matrix-org/synapse/pull/11114#discussion_r739300985
@@ -773,17 +773,17 @@ class FederationEventHandler:
 
         # We want to sort these by depth so we process them and
         # tell clients about them in order.
-        # sorted_events = sorted(events, key=lambda x: x.depth)
-
-        # We want to sort topologically so we process them and tell clients
-        # about them in order.
-        sorted_events = []
-        event_ids = [event.event_id for event in events]
-        event_map = {event.event_id: event for event in events}
-        event_id_graph = await self.generateEventIdGraphFromEvents(events)
-        for event_id in sorted_topologically(event_ids, event_id_graph):
-            sorted_events.append(event_map[event_id])
-        sorted_events = reversed(sorted_events)
+        sorted_events = sorted(events, key=lambda x: x.depth)
+
+        # # We want to sort topologically so we process them and tell clients
+        # # about them in order.
+        # sorted_events = []
+        # event_ids = [event.event_id for event in events]
+        # event_map = {event.event_id: event for event in events}
+        # event_id_graph = await self.generateEventIdGraphFromEvents(events)
+        # for event_id in sorted_topologically(event_ids, event_id_graph):
+        #     sorted_events.append(event_map[event_id])
+        # sorted_events = reversed(sorted_events)
 
         logger.info(
             "backfill sorted_events=%s",
diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py

index 4a4d35f77c..a569e8146a 100644
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -14,7 +14,7 @@
 import itertools
 import logging
 from queue import Empty, PriorityQueue
-from typing import Collection, Dict, Iterable, List, Optional, Set, Tuple
+from typing import Collection, Dict, Iterable, List, Optional, Set, Tuple, NamedTuple
 
 from prometheus_client import Counter, Gauge
 
@@ -53,6 +53,14 @@ pdus_pruned_from_federation_queue = Counter(
 logger = logging.getLogger(__name__)
 
 
+# All the info we need while iterating the DAG while backfilling
+class BackfillQueueNavigationItem(NamedTuple):
+    depth: int
+    stream_ordering: int
+    event_id: str
+    type: str
+
+
 class _NoChainCoverIndex(Exception):
     def __init__(self, room_id: str):
         super().__init__("Unexpectedly no chain cover for events in %s" % (room_id,))
@@ -987,6 +995,117 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
             "get_forward_extremeties_for_room", get_forward_extremeties_for_room_txn
         )
 
+    async def get_connected_insertion_event_backfill_results(
+        self, event_id: str, limit: int
+    ) -> List[BackfillQueueNavigationItem]:
+        def _get_connected_insertion_event_backfill_results_txn(txn):
+            # Look for the "insertion" events connected to the given event_id
+            connected_insertion_event_query = """
+                SELECT e.depth, e.stream_ordering, i.event_id, e.type FROM insertion_event_edges AS i
+                /* Get the depth of the insertion event from the events table */
+                INNER JOIN events AS e USING (event_id)
+                /* Find an insertion event which points via prev_events to the given event_id */
+                WHERE i.insertion_prev_event_id = ?
+                LIMIT ?
+            """
+
+            txn.execute(
+                connected_insertion_event_query,
+                (event_id, limit),
+            )
+            connected_insertion_event_id_results = txn.fetchall()
+            return [
+                BackfillQueueNavigationItem(
+                    depth=row[0],
+                    stream_ordering=row[1],
+                    event_id=row[2],
+                    type=row[3],
+                )
+                for row in connected_insertion_event_id_results
+            ]
+
+        return await self.db_pool.runInteraction(
+            "get_connected_insertion_event_backfill_results",
+            _get_connected_insertion_event_backfill_results_txn,
+        )
+
+    async def get_connected_batch_event_backfill_results(
+        self, insertion_event_id: str, limit: int
+    ) -> List[BackfillQueueNavigationItem]:
+        def _get_connected_batch_event_backfill_results_txn(txn):
+            # Find any batch connections of a given insertion event
+            batch_connection_query = """
+                SELECT e.depth, e.stream_ordering, c.event_id, e.type FROM insertion_events AS i
+                /* Find the batch that connects to the given insertion event */
+                INNER JOIN batch_events AS c
+                ON i.next_batch_id = c.batch_id
+                /* Get the depth of the batch start event from the events table */
+                INNER JOIN events AS e USING (event_id)
+                /* Find an insertion event which matches the given event_id */
+                WHERE i.event_id = ?
+                LIMIT ?
+            """
+
+            # Find any batch connections for the given insertion event
+            txn.execute(
+                batch_connection_query,
+                (insertion_event_id, limit),
+            )
+            batch_start_event_id_results = txn.fetchall()
+            return [
+                BackfillQueueNavigationItem(
+                    depth=row[0],
+                    stream_ordering=row[1],
+                    event_id=row[2],
+                    type=row[3],
+                )
+                for row in batch_start_event_id_results
+            ]
+
+        return await self.db_pool.runInteraction(
+            "get_connected_batch_event_backfill_results",
+            _get_connected_batch_event_backfill_results_txn,
+        )
+
+    async def get_connected_prev_event_backfill_results(
+        self, event_id: str, limit: int
+    ) -> List[BackfillQueueNavigationItem]:
+        def _get_connected_prev_event_backfill_results_txn(txn):
+            # Look for the prev_event_id connected to the given event_id
+            connected_prev_event_query = """
+                SELECT depth, stream_ordering, prev_event_id, events.type FROM event_edges
+                /* Get the depth and stream_ordering of the prev_event_id from the events table */
+                INNER JOIN events
+                ON prev_event_id = events.event_id
+                /* Look for an edge which matches the given event_id */
+                WHERE event_edges.event_id = ?
+                AND event_edges.is_state = ?
+                /* Because we can have many events at the same depth,
+                * we want to also tie-break and sort on stream_ordering */
+                ORDER BY depth DESC, stream_ordering DESC
+                LIMIT ?
+            """
+
+            txn.execute(
+                connected_prev_event_query,
+                (event_id, False, limit),
+            )
+            prev_event_id_results = txn.fetchall()
+            return [
+                BackfillQueueNavigationItem(
+                    depth=row[0],
+                    stream_ordering=row[1],
+                    event_id=row[2],
+                    type=row[3],
+                )
+                for row in prev_event_id_results
+            ]
+
+        return await self.db_pool.runInteraction(
+            "get_connected_prev_event_backfill_results",
+            _get_connected_prev_event_backfill_results_txn,
+        )
+
     async def get_backfill_events(self, room_id: str, event_list: list, limit: int):
         """Get a list of Events for a given topic that occurred before (and
         including) the events in event_list. Return a list of max size `limit`